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Wednesday, February 20, 2019

Retro-Networking: Cisco Router GRE Tunnels for transporting DECnet over IP using dynamips 7204VXR

Supratim Sanyal's Blog: DECnet GRE Tunneling Cisco Router


The wonderful dynamips emulator along with it's front-end dynagen allows us to relive the excitement of connecting remote machines speaking Digital Equipment Corporation's DECnet networking protocol over the internet using Generic Routing Encapsulation (GRE) tunnels.

I recently deployed a few dynamips-emulated instances of Cisco's venerable 7204VXR router and set up GRE tunnels between them to route DECnet as their passengers. This is a description of how I went about setting up one of those Cisco 7204VXR routers, and configured it as a GRE tunnel end-point. These routers implement the IP (internet protocol), DECnet and classic AppleTalk (Phase-1 and Phase-2) natively, and are a logical extension of my experiments with various classic computers and networking protocols collectively referred to as SANYALnet Labs.

At the time of writing, I have a GRE tunnel from my home to a VPS in Canada, and a second GRE tunnel from my home to a HECnet area router in Perth, Australia. The setup described in this post was performed on the VPS in Canada, running Ubuntu 14.04 LTS.

Not being a great GUI fan, I prefer the Cisco IOS (Internetwork Operating System) command line over graphical tools like GNS3.

Preparing Ubuntu Linux & UFW Firewall for GRE Protocol Support

Ubuntu Packages


Some of the packages I remember installing are dynamips, dynagen, bridge-utils, uml-utilities, ipcalc, vde2, wireshark, tshark.

Enable kernel support for GRE

Generic Routing Encapsulation (GRE) uses IANA-registered IP Protocol 47.  (A surprisingly large number of people confuse GRE/IP Protocol 47 withTCP/IP or UDP/IP Port 47.)

Since Microsoft's "PPTP" VPN implementation also uses GRE and is infamously insecure (no fault of GRE!), Ubuntu does not ship with support for GRE enabled. However, at least on Ubuntu 14.04, enabling GRE support is trivial. To load in GRE protocol support into the kernel, activate the nf_conntrack_pptp module using

# modprobe nf_conntrack_pptp

To load the module automatically at boot time, edit /etc/modules and add the line

nf_conntrack_pptp

To check the module is active:

$ lsmod | egrep "pptp|gre"

which should produce something like:

nf_conntrack_pptp      20480  0
nf_conntrack_proto_gre    16384  1 nf_conntrack_pptp
nf_conntrack          102400  6 nf_conntrack_proto_gre,nf_nat,nf_nat_ipv4,nf_nat_masquerade_ipv4,nf_conntrack_ipv4,nf_conntrack_pptp


Prep UFW Firewall for GRE

First follow these instructions to enable IP forwarding and ACCEPT rules in UFW. In effect, this boils down to:

1) Edit /etc/default/ufw and change the parameter:
    DEFAULT_FORWARD_POLICY="ACCEPT"

2) Edit /etc/ufw/sysctl.conf and enable by uncommenting:
    net.ipv4.ip_forward=1

Now we can add NAT rules for GRE tunnel and IP address forwarding to UFW firewall. Edit the file /etc/ufw/before.rules and add this at the very top:

*nat
:PREROUTING ACCEPT [0:0]
:POSTROUTING ACCEPT [0:0]

# GRE Tunnel protocol to CISCO Router
-A PREROUTING -i br-ip -p gre -j DNAT --to-destination 10.42.2.204
-A POSTROUTING -s 10.42.2.0/24 -o br-ip -j MASQUERADE

COMMIT


Reload UFW, or preferably, reboot.

Bridge, Tap and VDE setup

All of my Linux virtualization hosts are configured with the primary network adapter bridged to a local bridge into which I bridge in tap adapters and VDE switch plugs to support multiple virtual guests. This is important here because when we set up the NAT rules next, we will be using the bridge interface to NAT the dynamips Cisco router on the Linux host. Here is the script that sets up the bridge, tap and VDE:

#!/bin/bash
#
# ---
# bridge-tap-vde-setup.sh
# ---
# Bridge, VDE and Tun/Tap Network Device Setup Script to run emulators.
# Tested on Raspberry Pi Raspbian GNU/Linux 9 armv7l / 4.14.79-v7+
#
# Basically does this:
#
#   -------
#  |Network|
#  |Adapter|
#  |eth0   |
#   -------
#      |           ------
#       ----------|bridge|
#                 |br-ip |
#                  ------
#                    |         --------
#                    |--------|inettap0| <--> For use by TBD emulator
#                    |         --------
#                    |
#                    |         ----------
#                     --------|VDE Switch| (Virtual Distributed Ethernet switch)
#                              ----------
#                              |
#                              |  -----------
#                              |-|vde-ip-tap0| <--> Available to more TBD emulators
#                              |  -----------
#                              |
#                              |  -----------
#                              |-|vde-ip-tap1| <--> Available to more TBD emulators
#                              |  -----------
#
# More details:
# http://supratim-sanyal.blogspot.com/2018/10/bionic-beaver-on-zarchitecture-my.html
#
# Licensed under "THE BEER-WARE LICENSE" (Revision 42):
# Supratim Sanyal <https://goo.gl/FqzyBW> wrote this file. As long as
# you retain this notice you can do whatever you want with this stuff.
# If we meet some day, and you think this stuff is worth it, you can buy
# me a beer in return.
# ---

# ---
# Raspbian specific; dhcpcd is disabled as it was getting IP addresses for all taps and vdeplugs
# ---

# ----
# The physical interface that has the IP address which will be moved to a bridge and
# TAP and VDE plug interfaces made available from the bridge
# ----
DEVICE="eth0"

# ----
# No more changes should be required from here
# ----

HOSTIPANDMASK=`ip addr show dev $DEVICE | grep inet | head -1 | cut -f 6 -d " "`
HOSTIP=`echo $HOSTIPANDMASK|cut -f 1 -d "/"`
HOSTNETMASK=`echo $HOSTIPANDMASK|cut -f 2 -d "/"`
HOSTBCASTADDR=`ip addr show dev $DEVICE | grep inet | head -1 | cut -f 8 -d " "`
HOSTDEFAULTGATEWAY=`route -n | grep ^0.0.0.0 | gawk -- '{ print $2 }'`
NETWORK=`ipcalc $HOSTIP/$HOSTNETMASK | grep Network | cut -f 2 -d ":" | cut -f 1 -d "/" | tr -d '[:space:]'`

echo `date` ---- GATHERED INFORMATION -----
echo `date` HOSTIP=$HOSTIP HOSTNETMASK=$HOSTNETMASK NETWORK=$NETWORK HOSTBCASTADDR=$HOSTBCASTADDR HOSTDEFAULTGATEWAY=$HOSTDEFAULTGATEWAY
echo `date` -------------------------------

# ---
# Create a TAP network interface for emulators
# ---
ip tuntap add inettap0 mode tap user localuser

# ---
# Also create a VDE switch with TAP plugs for use by simuators
# ---

#
vde_switch -t vde-ip-tap0 -s /tmp/vde-ip.ctl -m 666 --mgmt /tmp/vde-ip.mgmt --mgmtmode 666 --daemon # spare plug
vde_plug2tap -s /tmp/vde-ip.ctl -m 666 -d vde-ip-tap1  # spare plug
#vde_plug2tap -s /tmp/vde-ip.ctl -m 666 -d vde-ip-tap2  # spare plug
#vde_plug2tap -s /tmp/vde-ip.ctl -m 666 -d vde-ip-tap3  # spare plug

# Create a Bridge
ip link add name br-ip type bridge
brctl stp br-ip on

# Bridge the NIC $DEVICE, the TAP device and VDE Switch TAP0 plug
ip link set $DEVICE master br-ip
ip link set inettap0 master br-ip
ip link set vde-ip-tap0 master br-ip

# Remove default route and move the IP address from $DEVICE to the bridge
ip route delete default via $HOSTDEFAULTGATEWAY dev $DEVICE
ip addr flush dev $DEVICE
ip addr add $HOSTIPANDMASK broadcast $HOSTBCASTADDR dev br-ip

# Bring everything back up
ip link set dev br-ip up
ip link set dev inettap0 up
ip link set vde-ip-tap0 up
ip link set vde-ip-tap1 up
#ip link set vde-ip-tap2 up
#ip link set vde-ip-tap3 up

# Reset the default route via the bridge interface which now has the IP
ip route add default via $HOSTDEFAULTGATEWAY dev br-ip

#echo `date` ---- NETWORK RECONFIGURED, WAITING TO SETTLE DOWN ----
#sleep 30

echo `date` ---- RELOADING UFW ----
ufw reload
sync

echo `date` ---- AFTER BRIDGE AND TAP ----
ip addr
echo `date` --- ROUTE ---
#ip route show
route -n
echo `date` --- BRIDGE ---
brctl show
#echo `date` --- IPTABLES ---
#iptables -L
echo `date` --- UFW ---
ufw status verbose
#echo `date` --- PING TEST ---
#ping -c 5 google.com
echo `date` -------------------------------

# --
# We can now attach simulators
# --
sync

Setting up the Local TAP Adapters

In addition, I created two local tap adapters for the Cisco router's NAT'd IP and standalone DECnet interfaces. The DECnet tap does not need to be connected to anything other than the Cisco router since DECnet will be tunneled over GRE using the NAT'd IP tap. Here is the script that sets up the local tap adapters and enables kernel IP forwarding. This is executed from /etc/rc.local right after the bridge/tap/VDE script above.

#!/bin/bash
# Sets up local taps

echo 1 > /proc/sys/net/ipv4/ip_forward

ip tuntap add ciscotap0 mode tap user localuser # DECnet -> CISCO f0/0
ip tuntap add ciscotap1 mode tap user localuser # IP -> CISCO f0/1
ifconfig ciscotap0 up
ifconfig ciscotap1 10.42.2.1 netmask 255.255.255.0 up

ufw reload

With the network configuration in place, we can assign a local IP 10.42.2.204 to our dynamips Cisco router and have the NAT iptables rules in UFW "before" configuration forward GRE packets to the Cisco router. Here is a summary of the network setup after a fresh reboot.

# ufw status
Status: active

To                         Action      From
--                         ------      ----
22                         LIMIT       Anywhere


# ip address
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master br-ip state UP group default qlen 1000
    link/ether 00:50:56:95:11:b8 brd ff:ff:ff:ff:ff:ff
3: inettap0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast master br-ip state DOWN group default qlen 1000
    link/ether 06:de:f9:f7:7e:4d brd ff:ff:ff:ff:ff:ff
4: vde-ip-tap0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master br-ip state UNKNOWN group default qlen 1000
    link/ether 5a:4b:b5:0f:a2:2d brd ff:ff:ff:ff:ff:ff
5: vde-ip-tap1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN group default qlen 1000
    link/ether 56:49:97:fa:43:d2 brd ff:ff:ff:ff:ff:ff
6: br-ip: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether 00:50:56:95:11:b8 brd ff:ff:ff:ff:ff:ff
    inet 64.137.160.124/24 brd 64.137.160.255 scope global br-ip
       valid_lft forever preferred_lft forever
7: ciscotap0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
    link/ether 26:bd:89:90:ca:ce brd ff:ff:ff:ff:ff:ff
8: ciscotap1: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
    link/ether ca:48:59:de:f0:9e brd ff:ff:ff:ff:ff:ff
    inet 10.42.2.1/24 brd 10.42.2.255 scope global ciscotap1
       valid_lft forever preferred_lft forever


route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         route.cloudatco 0.0.0.0         UG    0      0        0 br-ip
10.42.2.0       *               255.255.255.0   U     0      0        0 ciscotap1
64.137.160.0    *               255.255.255.0   U     0      0        0 br-ip

ip route show
default via 64.137.160.1 dev br-ip 
10.42.2.0/24 dev ciscotap1  proto kernel  scope link  src 10.42.2.1 

64.137.160.0/24 dev br-ip  proto kernel  scope link  src 64.137.160.124 

# iptables -t nat -L
Chain PREROUTING (policy ACCEPT)
target     prot opt source               destination         
DNAT       gre  --  anywhere             anywhere             to:10.42.2.204

Chain INPUT (policy ACCEPT)
target     prot opt source               destination         

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination         

Chain POSTROUTING (policy ACCEPT)
target     prot opt source               destination         
MASQUERADE  all  --  10.42.2.0/24         anywhere            


Setting up dynamips Cisco 7206VXR Routers for DECnet over GRE Tunnel

Router at Tunnel Endpoint

This is a description of one of the GRE tunnel end-points. The other GRE tunnel end-points are configured similarly, with obvious differences in destination IP addresses and their own DECnet and IP addresses etc.

Dynagen Configuration (vps4-cisco-7200.ini)

[localhost]
    workingdir = /home/localuser/cisco-router/dynagen_data
    model = 7200
    ghostios = true
    sparsemem = true
    [[7200]]
        image = /home/localuser/cisco-router/images/c7200-jk9o3s-mz.123-15.image
        npe = npe-400
        ram = 160
        idlepc = 0x60743ee8
    [[ROUTER R1]]
        s1/0 = R2 s1/0
#        f0/0 = NIO_linux_eth:vde-dnet-tap0
        f0/0 = NIO_tap:ciscotap0
#        f0/1 = NIO_linux_eth:inettap0
#        f0/1 = NIO_tap:inettap0
        f0/1 = NIO_tap:ciscotap1
    [[ROUTER R2]]


Startup Scripts

Both dynamips and dynagen run in virtual screen sessions using the "screen" ultility. Here are the two startup scripts.

# ----------run-dynamips-in-screen.sh 
#!/bin/bash

if /bin/pidof -x "dynamips" >/dev/null; then
logger "$0: dynamips already running, check screen -r cisco-router"
echo "$0: dynamips already running, check screen -r cisco-router"
        echo "screens:"
        /usr/bin/screen -ls
        exit 0
fi

cd ~/cisco-router/dynamips_data
#ifconfig vde-dnet-tap0 up
screen -S cisco-router -m -d nice -n 6 ionice -c2 dynamips -H 7200

sleep 2
screen -ls



# ---------- run-dynagen-in-screen.sh 
#!/bin/bash

if /bin/pidof -x "dynagen" >/dev/null; then
logger "$0: dynagen already running, check screen -r cisco-console"
echo "$0: dynagen already running, check screen -r cisco-console"
        echo "screens:"
        /usr/bin/screen -ls
        exit 0
fi

cd ~/cisco-router/
echo \"list\" to see list of routers
echo \"console R1\" to start xterm console to R1 router
echo OR telnet 10.42.2.204 OR telnet localhost 2000
echo \"start/all\" and \"stop/all\" to start and stop routers
echo \"exit\" also shuts down the routers but does not kill the emulator
echo \"screen -r cisco-router\" and ^C kills the dynamips emulator
screen -S cisco-console -m -d nice -n 6 ionice -c2 dynagen vps4-cisco-7200.ini

sleep 2
screen -ls


Router Configuration (show run)

!
version 12.3
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname CISCO-VPS4
!
boot-start-marker
boot-end-marker
!
enable secret 5 longgarbledstring
enable password redacted
!
no aaa new-model
ip subnet-zero
!
!
ip name-server 8.8.8.8
ip name-server 8.8.4.4
!
ip cef
ip audit po max-events 100
appletalk routing
!
decnet routing 1.919
decnet node-type routing-iv
!
!
!
!
!
!
!
!
!         
!
!
!
!
!

!
!
!
!
interface Tunnel1
 no ip address
 ip mtu 1400
 ip tcp adjust-mss 1360
 decnet cost 8
 decnet hello-timer 3
 decnet routing-timer 5
 tunnel source FastEthernet0/1
 tunnel destination 71.114.22.90
!
interface FastEthernet0/0
 no ip address
 duplex auto
 speed auto
 appletalk cable-range 10422-10422 10422.205
 appletalk zone SANYALnet
 decnet cost 8
 decnet hello-timer 2
 decnet routing-timer 4
!
interface FastEthernet0/1
 ip address 10.42.2.204 255.0.0.0
 ip broadcast-address 10.255.255.255
 duplex half
 speed auto
 no mop enabled
!         
interface Serial1/0
 no ip address
 shutdown
 serial restart-delay 0
!
interface Serial1/1
 no ip address
 shutdown
 serial restart-delay 0
!
interface Serial1/2
 no ip address
 shutdown
 serial restart-delay 0
!
interface Serial1/3
 no ip address
 shutdown
 serial restart-delay 0
!
interface Serial1/4
 no ip address
 shutdown
 serial restart-delay 0
!
interface Serial1/5
 no ip address
 shutdown
 serial restart-delay 0
!
interface Serial1/6
 no ip address
 shutdown
 serial restart-delay 0
!
interface Serial1/7
 no ip address
 shutdown
 serial restart-delay 0
!
ip default-gateway 10.42.2.1
ip classless
ip default-network 10.0.0.0
ip route 0.0.0.0 0.0.0.0 10.42.2.1
no ip http server
no ip http secure-server
!
!
dialer-list 1 protocol ip permit
dialer-list 1 protocol ipx permit
!
appletalk local-routing
decnet host MIM 1.13
!
!
!
!
!
!
!
gatekeeper
 shutdown
!
!
line con 0
 stopbits 1
line aux 0
 stopbits 1
line vty 0 4
 password redacted
 login
!
!
end


Router interfaces

$ telnet 10.42.2.204
Trying 10.42.2.204...
Connected to 10.42.2.204.
Escape character is '^]'.


User Access Verification

Password: 
CISCO-VPS4>enable
Password: 
CISCO-VPS4#show int
FastEthernet0/0 is up, line protocol is up 
  Hardware is i82543 (Livengood), address is aa00.0400.9707 (bia ca00.0b2d.0008)
  MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec, 
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 100Mb/s, 100BaseTX/FX
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input never, output 00:00:01, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 1 packets/sec
     0 packets input, 0 bytes
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog
     0 input packets with dribble condition detected
     1382 packets output, 89826 bytes, 0 underruns
     0 output errors, 0 collisions, 4 interface resets
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier
     0 output buffer failures, 0 output buffers swapped out
FastEthernet0/1 is up, line protocol is up 
  Hardware is i82543 (Livengood), address is ca00.0b2d.0006 (bia ca00.0b2d.0006)
  Internet address is 10.42.2.204/8
  MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec, 
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 100Mb/s, 100BaseTX/FX
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:00, output 00:00:00, output hang never
  Last clearing of "show interface" counters never
  Input queue: 1/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 4000 bits/sec, 3 packets/sec
  5 minute output rate 5000 bits/sec, 3 packets/sec
     1200 packets input, 449672 bytes
     Received 5 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog
     0 input packets with dribble condition detected
     1335 packets output, 754793 bytes, 0 underruns
     0 output errors, 0 collisions, 2 interface resets
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier
     0 output buffer failures, 0 output buffers swapped out
Serial1/0 is administratively down, line protocol is down 
  Hardware is M8T-X.21
  MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, 
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation HDLC, crc 16, loopback not set
  Keepalive set (10 sec)
  Restart-Delay is 0 secs
  Last input 00:18:48, output never, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: weighted fair
  Output queue: 0/1000/64/0 (size/max total/threshold/drops) 
     Conversations  0/0/256 (active/max active/max total)
     Reserved Conversations 0/0 (allocated/max allocated)
     Available Bandwidth 1158 kilobits/sec
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     4 packets input, 404 bytes, 0 no buffer
     Received 4 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     0 packets output, 0 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out
     1 carrier transitions     DCD=up  DSR=up  DTR=up  RTS=up  CTS=up

Serial1/1 is administratively down, line protocol is down 
  Hardware is M8T-X.21
  MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, 
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation HDLC, crc 16, loopback not set
  Keepalive set (10 sec)
  Restart-Delay is 0 secs
  Last input never, output never, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: weighted fair
  Output queue: 0/1000/64/0 (size/max total/threshold/drops) 
     Conversations  0/0/256 (active/max active/max total)
     Reserved Conversations 0/0 (allocated/max allocated)
     Available Bandwidth 1158 kilobits/sec
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     0 packets input, 0 bytes, 0 no buffer
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     0 packets output, 0 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out
     1 carrier transitions     DCD=down  DSR=down  DTR=up  RTS=up  CTS=down

Serial1/2 is administratively down, line protocol is down 
  Hardware is M8T-X.21
  MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, 
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation HDLC, crc 16, loopback not set
  Keepalive set (10 sec)
  Restart-Delay is 0 secs
  Last input never, output never, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: weighted fair
  Output queue: 0/1000/64/0 (size/max total/threshold/drops) 
     Conversations  0/0/256 (active/max active/max total)
     Reserved Conversations 0/0 (allocated/max allocated)
     Available Bandwidth 1158 kilobits/sec
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     0 packets input, 0 bytes, 0 no buffer
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     0 packets output, 0 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out
     1 carrier transitions     DCD=down  DSR=down  DTR=up  RTS=up  CTS=down

Serial1/3 is administratively down, line protocol is down 
  Hardware is M8T-X.21
  MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, 
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation HDLC, crc 16, loopback not set
  Keepalive set (10 sec)
  Restart-Delay is 0 secs
  Last input never, output never, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: weighted fair
  Output queue: 0/1000/64/0 (size/max total/threshold/drops) 
     Conversations  0/0/256 (active/max active/max total)
     Reserved Conversations 0/0 (allocated/max allocated)
     Available Bandwidth 1158 kilobits/sec
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     0 packets input, 0 bytes, 0 no buffer
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     0 packets output, 0 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out
     1 carrier transitions     DCD=down  DSR=down  DTR=up  RTS=up  CTS=down

Serial1/4 is administratively down, line protocol is down 
  Hardware is M8T-X.21
  MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, 
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation HDLC, crc 16, loopback not set
  Keepalive set (10 sec)
  Restart-Delay is 0 secs
  Last input never, output never, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: weighted fair
  Output queue: 0/1000/64/0 (size/max total/threshold/drops) 
     Conversations  0/0/256 (active/max active/max total)
     Reserved Conversations 0/0 (allocated/max allocated)
     Available Bandwidth 1158 kilobits/sec
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     0 packets input, 0 bytes, 0 no buffer
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     0 packets output, 0 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out
     1 carrier transitions     DCD=down  DSR=down  DTR=up  RTS=up  CTS=down

Serial1/5 is administratively down, line protocol is down 
  Hardware is M8T-X.21
  MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, 
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation HDLC, crc 16, loopback not set
  Keepalive set (10 sec)
  Restart-Delay is 0 secs
  Last input never, output never, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: weighted fair
  Output queue: 0/1000/64/0 (size/max total/threshold/drops) 
     Conversations  0/0/256 (active/max active/max total)
     Reserved Conversations 0/0 (allocated/max allocated)
     Available Bandwidth 1158 kilobits/sec
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     0 packets input, 0 bytes, 0 no buffer
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     0 packets output, 0 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out
     1 carrier transitions     DCD=down  DSR=down  DTR=up  RTS=up  CTS=down

Serial1/6 is administratively down, line protocol is down 
  Hardware is M8T-X.21
  MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, 
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation HDLC, crc 16, loopback not set
  Keepalive set (10 sec)
  Restart-Delay is 0 secs
  Last input never, output never, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: weighted fair
  Output queue: 0/1000/64/0 (size/max total/threshold/drops) 
     Conversations  0/0/256 (active/max active/max total)
     Reserved Conversations 0/0 (allocated/max allocated)
     Available Bandwidth 1158 kilobits/sec
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     0 packets input, 0 bytes, 0 no buffer
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     0 packets output, 0 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out
     1 carrier transitions     DCD=down  DSR=down  DTR=up  RTS=up  CTS=down

Serial1/7 is administratively down, line protocol is down 
  Hardware is M8T-X.21
  MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, 
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation HDLC, crc 16, loopback not set
  Keepalive set (10 sec)
  Restart-Delay is 0 secs
  Last input never, output never, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: weighted fair
  Output queue: 0/1000/64/0 (size/max total/threshold/drops) 
     Conversations  0/0/256 (active/max active/max total)
     Reserved Conversations 0/0 (allocated/max allocated)
     Available Bandwidth 1158 kilobits/sec
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     0 packets input, 0 bytes, 0 no buffer
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     0 packets output, 0 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out
     1 carrier transitions     DCD=down  DSR=down  DTR=up  RTS=up  CTS=down

Tunnel1 is up, line protocol is up 
  Hardware is Tunnel
  MTU 1514 bytes, BW 9 Kbit, DLY 500000 usec, 
     reliability 255/255, txload 170/255, rxload 85/255
  Encapsulation TUNNEL, loopback not set
  Keepalive not set
  Tunnel source 10.42.2.204 (FastEthernet0/1), destination 71.114.22.90
  Tunnel protocol/transport GRE/IP, key disabled, sequencing disabled
  Tunnel TTL 255
  Checksumming of packets disabled,  fast tunneling enabled
  Last input 00:00:00, output 00:00:02, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/0 (size/max)
  5 minute input rate 3000 bits/sec, 1 packets/sec
  5 minute output rate 6000 bits/sec, 1 packets/sec
     871 packets input, 452898 bytes, 0 no buffer
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     949 packets output, 705533 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out

CISCO-VPS4#show ip inter  
FastEthernet0/0 is up, line protocol is up
  Internet protocol processing disabled
FastEthernet0/1 is up, line protocol is up
  Internet address is 10.42.2.204/8
  Broadcast address is 10.255.255.255
  Address determined by non-volatile memory
  MTU is 1500 bytes
  Helper address is not set
  Directed broadcast forwarding is disabled
  Outgoing access list is not set
  Inbound  access list is not set
  Proxy ARP is enabled
  Local Proxy ARP is disabled
  Security level is default
  Split horizon is enabled
  ICMP redirects are always sent
  ICMP unreachables are always sent
  ICMP mask replies are never sent
  IP fast switching is enabled
  IP fast switching on the same interface is disabled
  IP Flow switching is disabled
  IP CEF switching is enabled
  IP Feature Fast switching turbo vector
  IP Feature CEF switching turbo vector
  IP multicast fast switching is enabled
  IP multicast distributed fast switching is disabled
  IP route-cache flags are Fast, CEF
  Router Discovery is disabled
  IP output packet accounting is disabled
  IP access violation accounting is disabled
  TCP/IP header compression is disabled
  RTP/IP header compression is disabled
  Policy routing is disabled
  Network address translation is disabled
  WCCP Redirect outbound is disabled
  WCCP Redirect inbound is disabled
  WCCP Redirect exclude is disabled
  BGP Policy Mapping is disabled
Serial1/0 is administratively down, line protocol is down
  Internet protocol processing disabled
Serial1/1 is administratively down, line protocol is down
  Internet protocol processing disabled
Serial1/2 is administratively down, line protocol is down
  Internet protocol processing disabled
Serial1/3 is administratively down, line protocol is down
  Internet protocol processing disabled
Serial1/4 is administratively down, line protocol is down
  Internet protocol processing disabled
Serial1/5 is administratively down, line protocol is down
  Internet protocol processing disabled
Serial1/6 is administratively down, line protocol is down
  Internet protocol processing disabled
Serial1/7 is administratively down, line protocol is down
  Internet protocol processing disabled
Tunnel1 is up, line protocol is up

  Internet protocol processing disabled

CISCO-VPS4#show appletalk int
FastEthernet0/0 is up, line protocol is up
  AppleTalk cable range is 10422-10422
  AppleTalk address is 10422.205, Valid
  AppleTalk zone is "SANYALnet"
  AppleTalk address gleaning is disabled
  AppleTalk route cache is enabled
FastEthernet0/1 is up, line protocol is up
  AppleTalk protocol processing disabled
Serial1/0 is administratively down, line protocol is down
  AppleTalk protocol processing disabled
Serial1/1 is administratively down, line protocol is down
  AppleTalk protocol processing disabled
Serial1/2 is administratively down, line protocol is down
  AppleTalk protocol processing disabled
Serial1/3 is administratively down, line protocol is down
  AppleTalk protocol processing disabled
Serial1/4 is administratively down, line protocol is down
  AppleTalk protocol processing disabled
Serial1/5 is administratively down, line protocol is down
  AppleTalk protocol processing disabled
Serial1/6 is administratively down, line protocol is down
  AppleTalk protocol processing disabled
Serial1/7 is administratively down, line protocol is down
  AppleTalk protocol processing disabled
Tunnel1 is up, line protocol is up

  AppleTalk protocol processing disabled

CISCO-VPS4#show decnet int
Global DECnet parameters for network 0:
  Local address is 1.919, node type is routing-iv
  Nearest Level-2 router is  1.579
  Maximum node is 1023, maximum area is 63, maximum visits is 63
  Maximum paths is 1, path split mode is normal 
  Local maximum cost is 1022, maximum hops is 30
  Area maximum cost is 1022, maximum hops is 30
  Static routes *NOT* being sent in routing updates
  Cluster-alias routes *NOT* being sent in routing updates
FastEthernet0/0 is up, line protocol is up, encapsulation is ARPA
  Interface cost is 8, priority is 64, DECnet network: 0
  We are the designated router
  Sending HELLOs every 2 seconds, routing updates 4 seconds
  PhaseIV VAX cluster hold time is 300 seconds
  Smallest router blocksize seen is 1498 bytes
  Routing input list is not set, output list is not set
  Access list is not set
  DECnet fast switching is enabled
  Number of L1 router adjacencies is : 0
  Number of L2 router adjacencies is : 0
  Number of non-PhaseIV+ router adjacencies is : 0
  Number of PhaseIV+ router adjacencies is : 0
FastEthernet0/1 is up, line protocol is up, encapsulation is ARPA
  DECnet protocol processing not enabled
Serial1/0 is administratively down, line protocol is down, encapsulation is HDLC
  DECnet protocol processing not enabled
Serial1/1 is administratively down, line protocol is down, encapsulation is HDLC
  DECnet protocol processing not enabled
Serial1/2 is administratively down, line protocol is down, encapsulation is HDLC
  DECnet protocol processing not enabled
Serial1/3 is administratively down, line protocol is down, encapsulation is HDLC
  DECnet protocol processing not enabled
Serial1/4 is administratively down, line protocol is down, encapsulation is HDLC
  DECnet protocol processing not enabled
Serial1/5 is administratively down, line protocol is down, encapsulation is HDLC
  DECnet protocol processing not enabled
Serial1/6 is administratively down, line protocol is down, encapsulation is HDLC
  DECnet protocol processing not enabled
Serial1/7 is administratively down, line protocol is down, encapsulation is HDLC
  DECnet protocol processing not enabled
Tunnel1 is up, line protocol is up, encapsulation is TUNNEL
  Interface cost is 8, priority is 64, DECnet network: 0
  The designated router is 1.579
  Sending HELLOs every 3 seconds, routing updates 5 seconds
  PhaseIV VAX cluster hold time is 300 seconds
  Smallest router blocksize seen is 1498 bytes
  Routing input list is not set, output list is not set
  Access list is not set
  DECnet fast switching is enabled
  Number of L1 router adjacencies is : 1
  Number of L2 router adjacencies is : 0
  Number of non-PhaseIV+ router adjacencies is : 0

  Number of PhaseIV+ router adjacencies is : 1


DECnet Route and Neighbors

CISCO-VPS4#show decnet route
  Node       Cost  Hops           Next Hop to Node       Expires  Prio
*(Area)        8     1             Tunnel1 -> 1.579  
*MIM          11     3             Tunnel1 -> 1.579  
*1.15         14     4             Tunnel1 -> 1.579  
*1.21         14     4             Tunnel1 -> 1.579  
*1.152        14     4             Tunnel1 -> 1.579  
*1.250        14     4             Tunnel1 -> 1.579  
*1.253        14     4             Tunnel1 -> 1.579  
*1.301        14     4             Tunnel1 -> 1.579  
*1.550        10     2             Tunnel1 -> 1.579  
*1.551        10     2             Tunnel1 -> 1.579  
*1.552        10     2             Tunnel1 -> 1.579  
*1.553        10     2             Tunnel1 -> 1.579  
*1.554        10     2             Tunnel1 -> 1.579  
*1.555        10     2             Tunnel1 -> 1.579  
*1.556        10     2             Tunnel1 -> 1.579  
*1.557        10     2             Tunnel1 -> 1.579  
*1.558        10     2             Tunnel1 -> 1.579  
*1.559        10     2             Tunnel1 -> 1.579  
*1.570        10     2             Tunnel1 -> 1.579  
*1.571        10     2             Tunnel1 -> 1.579  
*1.572        10     2             Tunnel1 -> 1.579  
*1.573        10     2             Tunnel1 -> 1.579  
*1.578        11     3             Tunnel1 -> 1.579  
*1.579         8     1             Tunnel1 -> 1.579          5     64  V+
*1.601        18     5             Tunnel1 -> 1.579  
*1.602        15     4             Tunnel1 -> 1.579  
*1.605        18     5             Tunnel1 -> 1.579  
*1.610        18     5             Tunnel1 -> 1.579  
*1.620        18     5             Tunnel1 -> 1.579  
*1.740        14     4             Tunnel1 -> 1.579  
*1.742        14     4             Tunnel1 -> 1.579  
*1.747        14     4             Tunnel1 -> 1.579  
*1.748        14     4             Tunnel1 -> 1.579  
*1.750        11     3             Tunnel1 -> 1.579  
*1.770        14     4             Tunnel1 -> 1.579  
*1.771        14     4             Tunnel1 -> 1.579  
*1.790        10     2             Tunnel1 -> 1.579  
*1.791        10     2             Tunnel1 -> 1.579  
*1.794        10     2             Tunnel1 -> 1.579  
*1.915        10     2             Tunnel1 -> 1.579  
*1.919         0     0             (Local) -> 1.919

CISCO-VPS4#show decnet neigh
Net Node     Interface            MAC address    Flags
0   1.579    Tunnel1              0000.0000.0000 V 


And finally, here is a section of tshark showing the traffic on the tap adapter that the Cisco router is connected to:

$ tshark -i ciscotap1
Capturing on 'ciscotap1'
    1 0.000000000  10.42.2.204 → 71.114.22.90 GRE 1474 Encapsulated 0x6003 (unknown)
    2 0.010244129  10.42.2.204 → 71.114.22.90 GRE 794 Encapsulated 0x6003 (unknown)
    3 1.255455372 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
    4 1.255474067 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
    5 1.980104275  10.42.2.204 → 71.114.22.90 GRE 74 Encapsulated 0x6003 (unknown)
    6 4.305465162 71.114.22.90 → 10.42.2.204  GRE 1474 Encapsulated 0x6003 (unknown)
    7 4.305927990 71.114.22.90 → 10.42.2.204  GRE 794 Encapsulated 0x6003 (unknown)
    8 4.992895607  10.42.2.204 → 71.114.22.90 GRE 1474 Encapsulated 0x6003 (unknown)
    9 5.003158079  10.42.2.204 → 71.114.22.90 GRE 794 Encapsulated 0x6003 (unknown)
   10 5.013470766  10.42.2.204 → 71.114.22.90 GRE 1474 Encapsulated 0x6003 (unknown)
   11 5.024216726  10.42.2.204 → 71.114.22.90 GRE 74 Encapsulated 0x6003 (unknown)
   12 5.680566436 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
   13 5.680590979 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
   14 7.998893518  10.42.2.204 → 71.114.22.90 GRE 74 Encapsulated 0x6003 (unknown)
   15 8.998245661 ca:00:0b:2d:00:06 → ca:00:0b:2d:00:06 LOOP 60 Reply
   16 10.009636083  10.42.2.204 → 71.114.22.90 GRE 1474 Encapsulated 0x6003 (unknown)
   17 10.019839161  10.42.2.204 → 71.114.22.90 GRE 794 Encapsulated 0x6003 (unknown)
   18 10.070231673 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
   19 10.070252853 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
   20 10.988181697  10.42.2.204 → 71.114.22.90 GRE 74 Encapsulated 0x6003 (unknown)
   21 11.553758599 71.114.22.90 → 10.42.2.204  GRE 1474 Encapsulated 0x6003 (unknown)
   22 11.553794355 71.114.22.90 → 10.42.2.204  GRE 794 Encapsulated 0x6003 (unknown)
   23 11.553835386 71.114.22.90 → 10.42.2.204  GRE 1474 Encapsulated 0x6003 (unknown)
   24 13.996455811  10.42.2.204 → 71.114.22.90 GRE 74 Encapsulated 0x6003 (unknown)
   25 14.562071262 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
   26 14.562090999 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
   27 15.010424154  10.42.2.204 → 71.114.22.90 GRE 1474 Encapsulated 0x6003 (unknown)
   28 15.020705509  10.42.2.204 → 71.114.22.90 GRE 794 Encapsulated 0x6003 (unknown)
   29 15.030982401  10.42.2.204 → 71.114.22.90 GRE 1474 Encapsulated 0x6003 (unknown)
   30 17.001990425  10.42.2.204 → 71.114.22.90 GRE 74 Encapsulated 0x6003 (unknown)
   31 18.995731534 ca:00:0b:2d:00:06 → ca:00:0b:2d:00:06 LOOP 60 Reply
   32 19.019175742 71.114.22.90 → 10.42.2.204  GRE 1474 Encapsulated 0x6003 (unknown)
   33 19.019194256 71.114.22.90 → 10.42.2.204  GRE 794 Encapsulated 0x6003 (unknown)
   34 19.019201092 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
   35 19.019207379 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
   36 19.992366335  10.42.2.204 → 71.114.22.90 GRE 1474 Encapsulated 0x6003 (unknown)
   37 20.008291743  10.42.2.204 → 71.114.22.90 GRE 794 Encapsulated 0x6003 (unknown)
   38 20.018516284  10.42.2.204 → 71.114.22.90 GRE 74 Encapsulated 0x6003 (unknown)
   39 22.997585210  10.42.2.204 → 71.114.22.90 GRE 74 Encapsulated 0x6003 (unknown)
   40 23.627106890 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
   41 23.627125349 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
   42 24.026321306 ca:48:59:de:f0:9e → ca:00:0b:2d:00:06 ARP 42 Who has 10.42.2.204? Tell 10.42.2.1
   43 24.030500265 ca:00:0b:2d:00:06 → ca:48:59:de:f0:9e ARP 60 10.42.2.204 is at ca:00:0b:2d:00:06
   44 25.009808182  10.42.2.204 → 71.114.22.90 GRE 1474 Encapsulated 0x6003 (unknown)
   45 25.021018991  10.42.2.204 → 71.114.22.90 GRE 794 Encapsulated 0x6003 (unknown)
   46 25.032683341  10.42.2.204 → 71.114.22.90 GRE 1474 Encapsulated 0x6003 (unknown)
   47 26.008328765  10.42.2.204 → 71.114.22.90 GRE 74 Encapsulated 0x6003 (unknown)
   48 26.543406661 71.114.22.90 → 10.42.2.204  GRE 1474 Encapsulated 0x6003 (unknown)
   49 26.543560700 71.114.22.90 → 10.42.2.204  GRE 794 Encapsulated 0x6003 (unknown)
   50 27.982440383 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
   51 27.982462059 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
   52 29.002420586  10.42.2.204 → 71.114.22.90 GRE 74 Encapsulated 0x6003 (unknown)
   53 29.012671361 ca:00:0b:2d:00:06 → ca:00:0b:2d:00:06 LOOP 60 Reply
   54 29.995583950  10.42.2.204 → 71.114.22.90 GRE 1474 Encapsulated 0x6003 (unknown)
   55 30.008222753  10.42.2.204 → 71.114.22.90 GRE 794 Encapsulated 0x6003 (unknown)
   56 31.983114902  10.42.2.204 → 71.114.22.90 GRE 74 Encapsulated 0x6003 (unknown)
   57 32.414551636 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
   58 32.414568952 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
   59 33.943888516 71.114.22.90 → 10.42.2.204  GRE 1474 Encapsulated 0x6003 (unknown)
   60 33.943910935 71.114.22.90 → 10.42.2.204  GRE 794 Encapsulated 0x6003 (unknown)
   61 33.943923202 71.114.22.90 → 10.42.2.204  GRE 1474 Encapsulated 0x6003 (unknown)
   62 35.001442315  10.42.2.204 → 71.114.22.90 GRE 1474 Encapsulated 0x6003 (unknown)
   63 35.011641874  10.42.2.204 → 71.114.22.90 GRE 794 Encapsulated 0x6003 (unknown)
   64 35.021859556  10.42.2.204 → 71.114.22.90 GRE 1474 Encapsulated 0x6003 (unknown)
   65 35.033380852  10.42.2.204 → 71.114.22.90 GRE 74 Encapsulated 0x6003 (unknown)
   66 36.954632224 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
   67 36.954649859 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
   68 38.000891414  10.42.2.204 → 71.114.22.90 GRE 74 Encapsulated 0x6003 (unknown)
   69 39.019368280 ca:00:0b:2d:00:06 → ca:00:0b:2d:00:06 LOOP 60 Reply
   70 39.993480364  10.42.2.204 → 71.114.22.90 GRE 1474 Encapsulated 0x6003 (unknown)
   71 40.003707088  10.42.2.204 → 71.114.22.90 GRE 794 Encapsulated 0x6003 (unknown)
   72 40.992456396  10.42.2.204 → 71.114.22.90 GRE 74 Encapsulated 0x6003 (unknown)
   73 41.465544624 71.114.22.90 → 10.42.2.204  GRE 1474 Encapsulated 0x6003 (unknown)
   74 41.465563272 71.114.22.90 → 10.42.2.204  GRE 794 Encapsulated 0x6003 (unknown)
   75 41.465573218 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
   76 41.465580377 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
   77 43.999177660  10.42.2.204 → 71.114.22.90 GRE 74 Encapsulated 0x6003 (unknown)
   78 44.989366697  10.42.2.204 → 71.114.22.90 GRE 1474 Encapsulated 0x6003 (unknown)
   79 44.999788934  10.42.2.204 → 71.114.22.90 GRE 794 Encapsulated 0x6003 (unknown)
   80 45.010053625  10.42.2.204 → 71.114.22.90 GRE 1474 Encapsulated 0x6003 (unknown)
   81 45.937675757 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
   82 45.937696001 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
   83 47.003696897  10.42.2.204 → 71.114.22.90 GRE 74 Encapsulated 0x6003 (unknown)
   84 48.850238460 71.114.22.90 → 10.42.2.204  GRE 1474 Encapsulated 0x6003 (unknown)
   85 48.850258954 71.114.22.90 → 10.42.2.204  GRE 794 Encapsulated 0x6003 (unknown)
   86 49.021398435 ca:00:0b:2d:00:06 → ca:00:0b:2d:00:06 LOOP 60 Reply
   87 49.997432676 ca:00:0b:2d:00:06 → CDP/VTP/DTP/PAgP/UDLD CDP 376 Device ID: CISCO-VPS4  Port ID: FastEthernet0/1  
   88 50.008011229  10.42.2.204 → 71.114.22.90 GRE 1474 Encapsulated 0x6003 (unknown)
   89 50.018237231  10.42.2.204 → 71.114.22.90 GRE 794 Encapsulated 0x6003 (unknown)
   90 50.028407881  10.42.2.204 → 71.114.22.90 GRE 74 Encapsulated 0x6003 (unknown)
   91 50.137707070 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
   92 50.137725521 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
   93 50.938322858 ca:48:59:de:f0:9e → ca:00:0b:2d:00:06 ARP 42 Who has 10.42.2.204? Tell 10.42.2.1
   94 50.940299813 ca:00:0b:2d:00:06 → ca:48:59:de:f0:9e ARP 60 10.42.2.204 is at ca:00:0b:2d:00:06
   95 53.007707715  10.42.2.204 → 71.114.22.90 GRE 74 Encapsulated 0x6003 (unknown)
   96 54.681849425 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
   97 54.681875191 71.114.22.90 → 10.42.2.204  GRE 74 Encapsulated 0x6003 (unknown)
   98 55.005911408  10.42.2.204 → 71.114.22.90 GRE 1474 Encapsulated 0x6003 (unknown)
   99 55.016207497  10.42.2.204 → 71.114.22.90 GRE 794 Encapsulated 0x6003 (unknown)
  100 55.026565784  10.42.2.204 → 71.114.22.90 GRE 1474 Encapsulated 0x6003 (unknown)
  101 55.990359246  10.42.2.204 → 71.114.22.90 GRE 74 Encapsulated 0x6003 (unknown)
  102 56.066812388 71.114.22.90 → 10.42.2.204  GRE 1474 Encapsulated 0x6003 (unknown)
  103 56.066833226 71.114.22.90 → 10.42.2.204  GRE 794 Encapsulated 0x6003 (unknown)
  104 56.066839699 71.114.22.90 → 10.42.2.204  GRE 1474 Encapsulated 0x6003 (unknown)
^C104 packets captured

CISCO GRE DECNet TUNNEL: A COMPLETE EXAMPLE

Here is another complete example of setting up a DECnet GRE tunnel between two Cisco routers. In this example, the local router at which we are executing the following commands has a NAT IP address of 10.42.2.204, and is NAT'd behind a Internet-facing gateway. The local DECnet address is 1.910, and the remote DECnet address is 1.919. We setup "tunnel0" to the remote router visible over the internet at 45.62.248.66. We can then successfully communicate with 1.919 over DECnet tunneled over GRE.

FastEthernet0/0 is connected to the DECnet-only network. FastEthernet0/1 is connected to the internet via the NAT host. DECnet and internet access are already verified to be working before configuring this tunnel.

Both are dynamips-emulated routers residing inside Ubuntu linux servers which have been configured to support GRE and NAT forwarding as described above.

In addition, we configure the NTP server on this router to keep and serve accurate time before exiting.


$ telnet 10.42.2.204
Trying 10.42.2.204...
Connected to 10.42.2.204.
Escape character is '^]'.


User Access Verification

Password: 
CISCO-VPS4>
CISCO-VPS4>
CISCO-VPS4>en
Password: 
CISCO-VPS4#
CISCO-VPS4#
CISCO-VPS4#config term
Enter configuration commands, one per line.  End with CNTL/Z.
CISCO-VPS4(config)#
CISCO-VPS4(config)#
CISCO-VPS4(config)#interface tunnel0
CISCO-VPS4(config-if)#description GRE tunnel for testing and experimentation
CISCO-VPS4(config-if)#no ip address
CISCO-VPS4(config-if)#logging event subif-link-status
CISCO-VPS4(config-if)#decnet cost 20
CISCO-VPS4(config-if)#decnet routing-timer 5
CISCO-VPS4(config-if)#decnet hello-timer 3
CISCO-VPS4(config-if)#tunnel source f0/1
CISCO-VPS4(config-if)#tunnel destination 45.62.248.66 !Cloud VPS 3
CISCO-VPS4(config-if)#tunnel path-mtu-discovery
CISCO-VPS4(config-if)#
CISCO-VPS4(config-if)#end
CISCO-VPS4#
CISCO-VPS4#write mem
Building configuration...
[OK]
CISCO-VPS4#
CISCO-VPS4#
CISCO-VPS4#show int tunnel0
Tunnel0 is up, line protocol is up 
  Hardware is Tunnel
  Description: GRE tunnel for testing and experimentation
  MTU 1514 bytes, BW 9 Kbit, DLY 500000 usec, 
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation TUNNEL, loopback not set
  Keepalive not set
  Tunnel source 10.42.2.204 (FastEthernet0/1), destination 45.62.248.66
  Tunnel protocol/transport GRE/IP, key disabled, sequencing disabled
  Tunnel TTL 255
  Checksumming of packets disabled,  fast tunneling enabled
  Path MTU Discovery, ager 10 mins, min MTU 92, MTU 0, expires never
  Last input never, output 00:00:01, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/0 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     0 packets input, 0 bytes, 0 no buffer
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     15 packets output, 795 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out
CISCO-VPS4#
CISCO-VPS4#
CISCO-VPS4#show decnet
Global DECnet parameters for network 0:
  Local address is 1.910, node type is routing-iv
  Nearest Level-2 router is  NONE
  Maximum node is 1023, maximum area is 63, maximum visits is 63
  Maximum paths is 1, path split mode is normal 
  Local maximum cost is 1022, maximum hops is 30
  Area maximum cost is 1022, maximum hops is 30
  Static routes *NOT* being sent in routing updates
  Cluster-alias routes *NOT* being sent in routing updates
CISCO-VPS4#
CISCO-VPS4#
CISCO-VPS4#
CISCO-VPS4#show ip
% Incomplete command.

CISCO-VPS4#
CISCO-VPS4#
CISCO-VPS4#show ip int
FastEthernet0/0 is up, line protocol is up
  Internet protocol processing disabled
FastEthernet0/1 is up, line protocol is up
  Internet address is 10.42.2.204/8
  Broadcast address is 10.255.255.255
  Address determined by non-volatile memory
  MTU is 1500 bytes
  Helper address is not set
  Directed broadcast forwarding is disabled
  Outgoing access list is not set
  Inbound  access list is not set
  Proxy ARP is enabled
  Local Proxy ARP is disabled
  Security level is default
  Split horizon is enabled
  ICMP redirects are always sent
  ICMP unreachables are always sent
  ICMP mask replies are never sent
  IP fast switching is enabled
  IP fast switching on the same interface is disabled
  IP Flow switching is disabled
  IP CEF switching is enabled
  IP Feature Fast switching turbo vector
  IP Feature CEF switching turbo vector
  IP multicast fast switching is enabled
  IP multicast distributed fast switching is disabled
  IP route-cache flags are Fast, CEF
  Router Discovery is disabled
  IP output packet accounting is disabled
  IP access violation accounting is disabled
  TCP/IP header compression is disabled
  RTP/IP header compression is disabled
  Policy routing is disabled
  Network address translation is disabled
  WCCP Redirect outbound is disabled
  WCCP Redirect inbound is disabled
  WCCP Redirect exclude is disabled
  BGP Policy Mapping is disabled
Serial1/0 is administratively down, line protocol is down
  Internet protocol processing disabled
Serial1/1 is administratively down, line protocol is down
  Internet protocol processing disabled
Serial1/2 is administratively down, line protocol is down
  Internet protocol processing disabled
Serial1/3 is administratively down, line protocol is down
  Internet protocol processing disabled
Serial1/4 is administratively down, line protocol is down
  Internet protocol processing disabled
Serial1/5 is administratively down, line protocol is down
  Internet protocol processing disabled
Serial1/6 is administratively down, line protocol is down
  Internet protocol processing disabled
Serial1/7 is administratively down, line protocol is down
  Internet protocol processing disabled
Tunnel0 is up, line protocol is up
  Internet protocol processing disabled
CISCO-VPS4#
CISCO-VPS4#
CISCO-VPS4#show decnet int
Global DECnet parameters for network 0:
  Local address is 1.910, node type is routing-iv
  Nearest Level-2 router is  NONE
  Maximum node is 1023, maximum area is 63, maximum visits is 63
  Maximum paths is 1, path split mode is normal 
  Local maximum cost is 1022, maximum hops is 30
  Area maximum cost is 1022, maximum hops is 30
  Static routes *NOT* being sent in routing updates
  Cluster-alias routes *NOT* being sent in routing updates
FastEthernet0/0 is up, line protocol is up, encapsulation is ARPA
  Interface cost is 20, priority is 64, DECnet network: 0
  We are the designated router
  Sending HELLOs every 2 seconds, routing updates 4 seconds
  PhaseIV VAX cluster hold time is 300 seconds
  Smallest router blocksize seen is 1498 bytes
  Routing input list is not set, output list is not set
  Access list is not set
  DECnet fast switching is enabled
  Number of L1 router adjacencies is : 0
  Number of L2 router adjacencies is : 0
  Number of non-PhaseIV+ router adjacencies is : 0
  Number of PhaseIV+ router adjacencies is : 0
FastEthernet0/1 is up, line protocol is up, encapsulation is ARPA
  DECnet protocol processing not enabled
Serial1/0 is administratively down, line protocol is down, encapsulation is HDLC
  DECnet protocol processing not enabled
Serial1/1 is administratively down, line protocol is down, encapsulation is HDLC
  DECnet protocol processing not enabled
Serial1/2 is administratively down, line protocol is down, encapsulation is HDLC
  DECnet protocol processing not enabled
Serial1/3 is administratively down, line protocol is down, encapsulation is HDLC
  DECnet protocol processing not enabled
Serial1/4 is administratively down, line protocol is down, encapsulation is HDLC
  DECnet protocol processing not enabled
Serial1/5 is administratively down, line protocol is down, encapsulation is HDLC
  DECnet protocol processing not enabled
Serial1/6 is administratively down, line protocol is down, encapsulation is HDLC
  DECnet protocol processing not enabled
Serial1/7 is administratively down, line protocol is down, encapsulation is HDLC
  DECnet protocol processing not enabled
Tunnel0 is up, line protocol is up, encapsulation is TUNNEL
  Interface cost is 20, priority is 64, DECnet network: 0
  Sending HELLOs every 3 seconds, routing updates 5 seconds
  PhaseIV VAX cluster hold time is 300 seconds
  Smallest router blocksize seen is 1498 bytes
  Routing input list is not set, output list is not set
  Access list is not set
  DECnet fast switching is enabled
  Number of L1 router adjacencies is : 0
  Number of L2 router adjacencies is : 0
  Number of non-PhaseIV+ router adjacencies is : 0
  Number of PhaseIV+ router adjacencies is : 0
CISCO-VPS4#
CISCO-VPS4#
CISCO-VPS4# ! ---------------
CISCO-VPS4# ! BRINGING THE OTHER TUNNEL END-POINT UP NOW 
CISCO-VPS4# ! ---------------    
CISCO-VPS4#
CISCO-VPS4#
CISCO-VPS4#show clock
*18:31:11.671 UTC Wed Feb 20 2019
CISCO-VPS4#
CISCO-VPS4>
CISCO-VPS4>show clock
*18:44:48.515 UTC Wed Feb 20 2019
CISCO-VPS4>
CISCO-VPS4>
CISCO-VPS4>! --
CISCO-VPS4>! TUNNEL ON OTHER SIDE IS NOW CONFIGURED (on VPS 3)
CISCO-VPS4>! --
CISCO-VPS4>
CISCO-VPS4>show int tunnel0
Tunnel0 is up, line protocol is up 
  Hardware is Tunnel
  Description: GRE tunnel for testing and experimentation
  MTU 1514 bytes, BW 9 Kbit, DLY 500000 usec, 
     reliability 255/255, txload 141/255, rxload 113/255
  Encapsulation TUNNEL, loopback not set
  Keepalive not set
  Tunnel source 10.42.2.204 (FastEthernet0/1), destination 45.62.248.66
  Tunnel protocol/transport GRE/IP, key disabled, sequencing disabled
  Tunnel TTL 255
  Checksumming of packets disabled,  fast tunneling enabled
  Path MTU Discovery, ager 10 mins, min MTU 92, MTU 0, expires never
  Last input 00:00:00, output 00:00:01, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/0 (size/max)
  5 minute input rate 4000 bits/sec, 1 packets/sec
  5 minute output rate 5000 bits/sec, 1 packets/sec
     618 packets input, 317086 bytes, 0 no buffer
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     644 packets output, 338314 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out
CISCO-VPS4>
CISCO-VPS4>
CISCO-VPS4>
CISCO-VPS4>show ip int 
FastEthernet0/0 is up, line protocol is up
  Internet protocol processing disabled
FastEthernet0/1 is up, line protocol is up
  Internet address is 10.42.2.204/8
  Broadcast address is 10.255.255.255
  Address determined by non-volatile memory
  MTU is 1500 bytes
  Helper address is not set
  Directed broadcast forwarding is disabled
  Outgoing access list is not set
  Inbound  access list is not set
  Proxy ARP is enabled
  Local Proxy ARP is disabled
  Security level is default
  Split horizon is enabled
  ICMP redirects are always sent
  ICMP unreachables are always sent
  ICMP mask replies are never sent
  IP fast switching is enabled
  IP fast switching on the same interface is disabled
  IP Flow switching is disabled
  IP CEF switching is enabled
  IP Feature Fast switching turbo vector
  IP Feature CEF switching turbo vector
  IP multicast fast switching is enabled
  IP multicast distributed fast switching is disabled
  IP route-cache flags are Fast, CEF
  Router Discovery is disabled
  IP output packet accounting is disabled
  IP access violation accounting is disabled
  TCP/IP header compression is disabled
  RTP/IP header compression is disabled
  Policy routing is disabled
  Network address translation is disabled
  WCCP Redirect outbound is disabled
  WCCP Redirect inbound is disabled
  WCCP Redirect exclude is disabled
  BGP Policy Mapping is disabled
Serial1/0 is administratively down, line protocol is down
  Internet protocol processing disabled
Serial1/1 is administratively down, line protocol is down
  Internet protocol processing disabled
Serial1/2 is administratively down, line protocol is down
  Internet protocol processing disabled
Serial1/3 is administratively down, line protocol is down
  Internet protocol processing disabled
Serial1/4 is administratively down, line protocol is down
  Internet protocol processing disabled
Serial1/5 is administratively down, line protocol is down
  Internet protocol processing disabled
Serial1/6 is administratively down, line protocol is down
  Internet protocol processing disabled
Serial1/7 is administratively down, line protocol is down
  Internet protocol processing disabled
Tunnel0 is up, line protocol is up
  Internet protocol processing disabled
CISCO-VPS4>
CISCO-VPS4>
CISCO-VPS4>
CISCO-VPS4>show decnet int
Global DECnet parameters for network 0:
  Local address is 1.910, node type is routing-iv
  Nearest Level-2 router is  1.919
  Maximum node is 1023, maximum area is 63, maximum visits is 63
  Maximum paths is 1, path split mode is normal 
  Local maximum cost is 1022, maximum hops is 30
  Area maximum cost is 1022, maximum hops is 30
  Static routes *NOT* being sent in routing updates
  Cluster-alias routes *NOT* being sent in routing updates
FastEthernet0/0 is up, line protocol is up, encapsulation is ARPA
  Interface cost is 20, priority is 64, DECnet network: 0
  We are the designated router
  Sending HELLOs every 2 seconds, routing updates 4 seconds
  PhaseIV VAX cluster hold time is 300 seconds
  Smallest router blocksize seen is 1498 bytes
  Routing input list is not set, output list is not set
  Access list is not set
  DECnet fast switching is enabled
  Number of L1 router adjacencies is : 0
  Number of L2 router adjacencies is : 0
  Number of non-PhaseIV+ router adjacencies is : 0
  Number of PhaseIV+ router adjacencies is : 0
FastEthernet0/1 is up, line protocol is up, encapsulation is ARPA
  DECnet protocol processing not enabled
Serial1/0 is administratively down, line protocol is down, encapsulation is HDLC
  DECnet protocol processing not enabled
Serial1/1 is administratively down, line protocol is down, encapsulation is HDLC
  DECnet protocol processing not enabled
Serial1/2 is administratively down, line protocol is down, encapsulation is HDLC
  DECnet protocol processing not enabled
Serial1/3 is administratively down, line protocol is down, encapsulation is HDLC
  DECnet protocol processing not enabled
Serial1/4 is administratively down, line protocol is down, encapsulation is HDLC
  DECnet protocol processing not enabled
Serial1/5 is administratively down, line protocol is down, encapsulation is HDLC
  DECnet protocol processing not enabled
Serial1/6 is administratively down, line protocol is down, encapsulation is HDLC
  DECnet protocol processing not enabled
Serial1/7 is administratively down, line protocol is down, encapsulation is HDLC
  DECnet protocol processing not enabled
Tunnel0 is up, line protocol is up, encapsulation is TUNNEL
  Interface cost is 20, priority is 64, DECnet network: 0
  The designated router is 1.919
  Sending HELLOs every 3 seconds, routing updates 5 seconds
  PhaseIV VAX cluster hold time is 300 seconds
  Smallest router blocksize seen is 1498 bytes
  Routing input list is not set, output list is not set
  Access list is not set
  DECnet fast switching is enabled
  Number of L1 router adjacencies is : 1
  Number of L2 router adjacencies is : 0
  Number of non-PhaseIV+ router adjacencies is : 0
  Number of PhaseIV+ router adjacencies is : 1
CISCO-VPS4>
CISCO-VPS4>! -- ^^^ 1.919 is on the other end of the tunnel (on VPS3) --
CISCO-VPS4>
CISCO-VPS4>show decnet neigh
Net Node     Interface            MAC address    Flags
0   1.919    Tunnel0              0000.0000.0000 V 
CISCO-VPS4>
CISCO-VPS4>! -- ^^^ 1.919 is on the other end of the tunnel (on VPS3) --
CISCO-VPS4>
CISCO-VPS4>
CISCO-VPS4>                                                             
CISCO-VPS4>
CISCO-VPS4>show decnet route
  Node       Cost  Hops           Next Hop to Node       Expires  Prio
*(Area)       20     1             Tunnel0 -> 1.919  
*MIM          41     3             Tunnel0 -> 1.919  
*1.15         44     4             Tunnel0 -> 1.919  
*1.21         44     4             Tunnel0 -> 1.919  
*1.152        44     4             Tunnel0 -> 1.919  
*1.250        44     4             Tunnel0 -> 1.919  
*1.253        44     4             Tunnel0 -> 1.919  
*1.301        44     4             Tunnel0 -> 1.919  
*1.550        40     2             Tunnel0 -> 1.919  
*1.551        40     2             Tunnel0 -> 1.919  
*1.552        40     2             Tunnel0 -> 1.919  
*1.553        40     2             Tunnel0 -> 1.919  
*1.554        40     2             Tunnel0 -> 1.919  
*1.555        40     2             Tunnel0 -> 1.919  
*1.556        40     2             Tunnel0 -> 1.919  
*1.557        40     2             Tunnel0 -> 1.919  
*1.558        40     2             Tunnel0 -> 1.919  
*1.559        40     2             Tunnel0 -> 1.919  
*1.570        40     2             Tunnel0 -> 1.919  
*1.571        40     2             Tunnel0 -> 1.919  
*1.572        40     2             Tunnel0 -> 1.919  
*1.573        40     2             Tunnel0 -> 1.919  
*1.578        41     3             Tunnel0 -> 1.919  
*1.579        40     2             Tunnel0 -> 1.919  
*1.601        48     5             Tunnel0 -> 1.919  
*1.602        45     4             Tunnel0 -> 1.919  
*1.605        48     5             Tunnel0 -> 1.919  
*1.610        48     5             Tunnel0 -> 1.919  
*1.620        48     5             Tunnel0 -> 1.919  
*1.740        44     4             Tunnel0 -> 1.919  
*1.742        44     4             Tunnel0 -> 1.919  
*1.747        44     4             Tunnel0 -> 1.919  
*1.748        44     4             Tunnel0 -> 1.919  
*1.750        41     3             Tunnel0 -> 1.919  
*1.770        44     4             Tunnel0 -> 1.919  
*1.771        44     4             Tunnel0 -> 1.919  
*1.790        40     2             Tunnel0 -> 1.919  
*1.791        40     2             Tunnel0 -> 1.919  
*1.794        40     2             Tunnel0 -> 1.919  
*1.910         0     0             (Local) -> 1.910
*1.915        40     2             Tunnel0 -> 1.919  
*1.919        20     1             Tunnel0 -> 1.919          9     64  V+
CISCO-VPS4>! -- ^^^ 1.919 is on the other end of the tunnel (on VPS3) --
CISCO-VPS4>
CISCO-VPS4>! -- configure NTP --
CISCO-VPS4>
CISCO-VPS4>
CISCO-VPS4>en
Password: 
CISCO-VPS4#config term
Enter configuration commands, one per line.  End with CNTL/Z.
CISCO-VPS4(config)#
CISCO-VPS4(config)#
CISCO-VPS4(config)#ntp master
CISCO-VPS4(config)#ntp server 132.163.97.3
CISCO-VPS4(config)#ntp server 132.163.97.2
CISCO-VPS4(config)#ntp server 132.163.97.4
CISCO-VPS4(config)#ntp server 129.6.15.30
CISCO-VPS4(config)#ntp server 129.6.15.29
CISCO-VPS4(config)#ntp server 129.6.15.27
CISCO-VPS4(config)#
CISCO-VPS4(config)#end
CISCO-VPS4#write mem
Building configuration...
[OK]
CISCO-VPS4#
CISCO-VPS4#
CISCO-VPS4#show ntp status
Clock is synchronized, stratum 2, reference is 132.163.97.2
nominal freq is 250.0000 Hz, actual freq is 250.0000 Hz, precision is 2**18
reference time is E0181FBA.50A7E9C6 (18:49:30.315 UTC Wed Feb 20 2019)
clock offset is 123.4686 msec, root delay is 104.31 msec
root dispersion is 533.52 msec, peer dispersion is 405.08 msec
CISCO-VPS4#
CISCO-VPS4#show ntp assoc

      address         ref clock     st  when  poll reach  delay  offset    disp
 ~132.163.97.3     0.0.0.0          16     -    64    0     0.0    0.00  16000.
-~132.163.97.2     .NIST.            1    18    64  334   104.1  127.96   386.3
+~132.163.97.4     .NIST.            1     6    64  367    64.0  108.58     3.5
 ~127.127.7.1      127.127.7.1       7     4    64  377     0.0    0.00     0.0
-~129.6.15.30      .NIST.            1    18    64   20    60.0  126.04  16000.
*~129.6.15.29      .NIST.            1    12    64  275    36.0  107.80     5.0
+~129.6.15.27      .NIST.            1    13    64  131    56.1  110.82   380.3
 * master (synced), # master (unsynced), + selected, - candidate, ~ configured
CISCO-VPS4#
CISCO-VPS4#
CISCO-VPS4#      
CISCO-VPS4#write mem
Building configuration...
[OK]
CISCO-VPS4#logout
Connection closed by foreign host.

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