Nicholas Morrison - Networking Specialist

S1E4 - Introduction to the Arista CLI, continued

Connecting to the Lab Server

To quickly delete an old ssh fingerprint from your known_hosts file:

$ ssh-keygen -R
# Host found: line 83
# Host found: line 84
/Users/nickm/.ssh/known_hosts updated.
Original contents retained as /Users/nickm/.ssh/known_hosts.old

To connect to the lab server:

$ ssh [email protected]
The authenticity of host ' (' can't be established.
ED25519 key fingerprint is SHA256:x/Rrd66apuL9new7ewxpcR7cuKg9/yHL/JejJzPxmBk.
This host key is known by the following other names/addresses:
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added '' (ED25519) to the list of known hosts.
[email protected]'s password: (provided elsewhere!)


Topology: five-routers-five-pcs

If you want to, you can clone this repository to your own computer. This isn’t necessary to complete the workshop!

$ git clone [email protected]:nickm/networking-workshops.git
$ cd networking-workshops/topologies
$ ls -la


Topology: five-routers-five-pcs

The Final Goal

All PCs (pc1 through pc5) should be able to ping one another.

  • Work step by step!
  • Refer to s1e3-arista-cli for reminders (perhaps keep this open in a tab for reference)
  • Ask questions
  • Experiment! You can’t break anything.

Step 1 - configure eth1

The first step is to configure the IP address on your router’s eth1 interface.


$ sudo containerlab inspect --all          <- show all running devices
$ sudo docker exec -it DEVICE-NAME Cli     <- connect to an Arista

Configure as follows:

rX#config                                   <- enter configuration mode

rX(config)#interface eth1                   <- enter the interface
                                               configuration context

rX(config-if-eth1)#show active              <- shows the configuration
                                               just for this context

rX(config-if-eth1)#description to Switch    <- create a human-readable
                                               description for this

rX(config-if-eth1)#no switchport            <- make this a routed (L3)
                                               port (default is switched
                                               (L2) port)

rX(config-if-eth1)#ip address 10.0.0.x/24   <- refer to the diagram
rX(config-if-eth1)#show active
rX(config-if-eth1)#end                      <- exit configuration mode

rX#show ip interface brief                  <- print a list of all
                                               interfaces with an IPv4
                                               (L3) address

Test by seeing if you can ping another router’s IP address! You might need to ask your lab-mates whether they have already configured their devices.

rX#ping 10.0.0.X

Step 2 - configure eth2

This is the interface that connects to the PC.

This interface will serve as the default gateway or gateway of last resort for the PC.

Configure as follows:

rX(config)#interface eth2
rX(config-if-eth2)#show active
rX(config-if-eth2)#description to PC
rX(config-if-eth2)#no switchport
rX(config-if-eth2)#ip address 192.168.X.1/24   <- refer to the diagram
rX(config-if-eth2)#show active
rX(config-if-eth2)#end                      <- fully exit configuration mode
rX#show ip interface brief                  <- print a list of all interfaces with a IPv4 (L3) address

Test to see if you can ping your PC (192.168.X.2)

rX#ping 192.168.X.2

Step 3 - configure some static routes

  • The when the router receives a packet, it checks the destination of the packet to decide which interface to forward it out of.
  • The router uses a routing table to make this decision.
  • There are different ways for a routing table to become populated with data.
    • Static routes
    • Dynamic routes

Configure a static route:

rX#show ip route                              <- take a look at the routing table
rX(config)#ip route 192.168.X.0/24 10.0.0.X   <- when I have a packet that is destined for
                                                 192.168.X.something, forward it on to 10.0.0.x
rX#show ip route                              <- take another look at the routing table

Repeat this for all of the remote networks.

Test by pinging a remote PC from your own PC. You might have to check with the other lab members to make sure they’re up and running.

pcX$ ping 192.168.X.2

You can also try a traceroute:

pcX$ traceroute -n 192.168.X.2    <- the -n tells traceroute not to try to resolve the IP
                                     addresses into names

Things to try

  • Run a tcpdump on your router:
$ tcpdump -i eth1 icmp             <- listen for traffic on eth1, and only print ICMP (ping) packets
(press ctrl-c to terminate tcpdump)
  • Watch what happens when you send a successful ping
  • .. or an unsuccessful ping
  • .. or a ping to an unknown network


  • Are the routers in the same network, or different networks?
  • Which devices are in the same network as the PCs?