Imagine you have an IPv4-only network¹ and want to try out how to deploy a routing protocol for IPv6. netlab is a pretty good tool for the job as it:

• Creates an addressing scheme for you
• Designs a routing protocol deployment (OSPF, IS-IS) based on just a few bits of information
• Deploys ready-to-run router configurations to a virtual lab.

If you’re focused on testing a routing protocol deployment, you wouldn’t want to waste time configuring IPv6 addressing, so you should adjust the addressing pools to include IPv6 prefixes:

addressing:
  loopback.ipv6: 2001:db8:cafe::/48    # Routers are always debating stuff
  p2p.ipv6: True                       # Use LLA-only P2P links
  lan.ipv6: 3fff:1::/48                # Hey, we got RFC 9637

However, when you deploy OSPF (for example) in your network, netlab tries to be extra helpful and configures both OSPFv2 and OSPFv3.

Let’s use this simple topology with the above addressing pools:

defaults.device: eos
provider: clab
module: [ ospf ]

nodes: [ r1, r2 ]
links: [ r1, r1-r2, r2 ]

After starting the lab, R1 gets the following OSPF-related configuration:

interface Ethernet1
   description r1 -> stub [stub]
   ip address 172.16.0.1/24
   ipv6 address 3fff:1::1/64
   ip ospf network point-to-point
   ip ospf area 0.0.0.0
   ipv6 ospf network point-to-point
   ipv6 ospf 1 area 0.0.0.0
!
interface Ethernet2
   description r1 -> r2
   ip address 10.1.0.1/30
   ipv6 enable
   ip ospf network point-to-point
   ip ospf area 0.0.0.0
   ipv6 ospf network point-to-point
   ipv6 ospf 1 area 0.0.0.0
!
interface Loopback0
   ip address 10.0.0.1/32
   ipv6 address 2001:db8:cafe:1::1/64
   ip ospf area 0.0.0.0
   ipv6 ospf 1 area 0.0.0.0
!
router ospf 1
   router-id 10.0.0.1
   interface unnumbered hello mask tx 0.0.0.0
   passive-interface Ethernet1
   max-lsa 12000
   timers spf delay initial 100 200 500
   timers lsa rx min interval 100
   timers lsa tx delay initial 100 200 500
!
ipv6 router ospf 1
   router-id 10.0.0.1
   passive-interface Ethernet1
   timers spf delay initial 100 200 500
   timers lsa rx min interval 100
   timers lsa tx delay initial 100 200 500

Not exactly what we wanted – we’d love to have OSPFv2 configured, but not OSPFv3.

Other netlab users tried to solve a similar problem in the past, so we added support for configurable IGP address families a while ago. All we have to do to deploy OSPFv2, but not OSPFv3, is a single global parameter:

ospf.af: [ ipv4 ]

Here’s the OSPF-related configuration deployed to R1 after we limited OSPF deployment to IPv4:

interface Ethernet1
   description r1 -> stub [stub]
   ip address 172.16.0.1/24
   ipv6 address 3fff:1::1/64
   ip ospf network point-to-point
   ip ospf area 0.0.0.0
!
interface Ethernet2
   description r1 -> r2
   ip address 10.1.0.1/30
   ipv6 enable
   ip ospf network point-to-point
   ip ospf area 0.0.0.0
!
interface Loopback0
   ip address 10.0.0.1/32
   ipv6 address 2001:db8:cafe:1::1/64
   ip ospf area 0.0.0.0
!
router ospf 1
   router-id 10.0.0.1
   interface unnumbered hello mask tx 0.0.0.0
   passive-interface Ethernet1
   max-lsa 12000
   timers spf delay initial 100 200 500
   timers lsa rx min interval 100
   timers lsa tx delay initial 100 200 500

netlab configured IPv4 and IPv6 addresses, but not OSPFv3. Mission Accomplished.

Kicking the Tires

You can try out this example in your own netlab environment (installation guide or in free GitHub Codespaces.

If you set up your own netlab environment, execute netlab up https://github.com/ipspace/netlab-examples/blob/master/OSPF/ipv4-only/topology.yml in an empty directory. If you didn’t install Arista cEOS containers, add -d frr to the command.

In a GitHub Codespace:

• Install Arista cEOS container image
• Change directory to OSPF/ipv4-only
• Execute netlab up, or netlab up -d frr to use FRRouting if you didn’t install the Arista cEOS container image.