The lab
Four routers in a line, each in its own AS:
| Router | Role | IPv4 | IPv6 |
|---|---|---|---|
| C1 (FRR, AS64512) | Customer; originates 198.51.100.0/24 | Only on its loopback (198.51.100.1) | 2001:db8:0:1::2 towards R1 |
| R1 (VyOS, AS64500) | Pure core: no IPv4 at all | none | 2001:db8:0:1::1, 2001:db8:0:2::1 |
| R2 (VyOS, AS64501) | Provider edge | 192.0.2.1/30 towards C2 only | 2001:db8:0:2::2 towards R1 |
| C2 (FRR, AS64502) | IPv4-only customer; originates 203.0.113.0/24 | 192.0.2.2/30 and loopback 203.0.113.1 | none (link-local only) |
C1 already offers the extended next hop capability (capability extended-nexthop in its FRR config). The VyOS routers start without it, so you can see what changes when it's turned on.
frr defaults traditional
hostname c1
!
interface eth0
ipv6 address 2001:db8:0:1::2/64
!
interface lo
ip address 198.51.100.1/32
!
ip route 198.51.100.0/24 Null0
!
router bgp 64512
bgp router-id 198.51.100.1
no bgp ebgp-requires-policy
no bgp default ipv4-unicast
neighbor 2001:db8:0:1::1 remote-as 64500
neighbor 2001:db8:0:1::1 capability extended-nexthop
!
address-family ipv4 unicast
network 198.51.100.0/24
neighbor 2001:db8:0:1::1 activate
exit-address-family
exit
!- Lines 4–5: Only IPv6 on the link to R1.
- Lines 7–8: Its only IPv4 address is on the loopback.
- Line 16: An IPv6 neighbor…
- Line 17: …offering the extended next hop capability.
- Lines 19–22: Carrying IPv4 unicast.
frr defaults traditional
hostname c2
!
interface eth0
ip address 192.0.2.2/30
!
interface lo
ip address 203.0.113.1/32
!
ip route 203.0.113.0/24 Null0
!
router bgp 64502
bgp router-id 203.0.113.1
no bgp ebgp-requires-policy
neighbor 192.0.2.1 remote-as 64501
!
address-family ipv4 unicast
network 203.0.113.0/24
exit-address-family
exit
!- Lines 4–5: Plain IPv4 on the link to R2.
- Lines 15–19: An ordinary IPv4 BGP session.