topic Re: Strange BGP announcement of a /31 network as /32 in General Topics

Strange BGP announcement of a /31 network as /32

metalhead — Thu, 07 Aug 2025 12:50:09 GMT

I experience a strange BGP behavior.

R82 with VSNext.

VS instance has wrp66 configured with a /31 network mask

BGP announcement for this directly attached network is a /32 network

[Global] FWxxx-s01-01:1> show route
1_01:
Codes: C - Connected, S - Static, R - RIP, B - BGP (D - Default),
O - OSPF IntraArea (IA - InterArea, E - External, N - NSSA),
IS - IS-IS (L1 - Level 1, L2 - Level 2, IA - InterArea, E - External),
A - Aggregate, K - Kernel Remnant, H - Hidden, P - Suppressed,
NP - NAT Pool, U - Unreachable, i - Inactive

[...]
C 10.1.64.128/32 is directly connected, wrp66
VLAN16
[...]

---

[Global] FWxxx-s01-01:1> show interface wrp66
1_01:
state on
mac-addr 00:12:c1:xx:xx:xx
type wrp
link-state not available
instance 1
mtu 1500
auto-negotiation off
speed N/A
ipv6-autoconfig Not configured
monitor-mode Not configured
duplex N/A
link-speed Not configured
comments VLAN16
ipv4-address 10.1.64.128/31
ipv6-address Not Configured
ipv6-local-link-address Not Configured

On a different VS with a different /31 IP range the VS correctly announces the /31 network.

Thanks Tom

Re: Strange BGP announcement of a /31 network as /32

the_rock — Thu, 07 Aug 2025 13:29:56 GMT

I had that happen once with a customer and we fixed it by running bgp restart all from clish.

Andy

Re: Strange BGP announcement of a /31 network as /32

metalhead — Thu, 07 Aug 2025 13:50:52 GMT

Yes thanks - I recreated the interface and now its working --- strange to advertise a /32 route 🙂

Re: Strange BGP announcement of a /31 network as /32

the_rock — Thu, 07 Aug 2025 13:56:23 GMT

Excellent!

Re: Strange BGP announcement of a /31 network as /32

Chris_Atkinson — Fri, 08 Aug 2025 02:13:23 GMT

What the corresponding BGP config that's being used out of interest?

Note also sk91020 says this is unsupported for VSX (traditional) have asked to have the SK updated for VSNext where relevant.

Re: Strange BGP announcement of a /31 network as /32

metalhead — Thu, 11 Sep 2025 09:31:57 GMT

Hi Chris,

what infos in regards to BGP config do you need ?

In regards to support I can configure a /31 subnet mask in GAiA on R82 VSNext.

Re: Strange BGP announcement of a /31 network as /32

Chris_Atkinson — Thu, 11 Sep 2025 13:26:16 GMT

The relevant config for advertising the route/s to help recreate it, are you simply redistributing connected or some other approach / combination?

If you're more comfortable by all means share this via TAC for a proper investigation

Re: Strange BGP announcement of a /31 network as /32

metalhead — Thu, 18 Sep 2025 12:00:45 GMT

I simply configured the Interface to be redistributed in GAiA "Advanced Routing" -> "Route Redistribution"

Re: Strange BGP announcement of a /31 network as /32

the_rock — Thu, 18 Sep 2025 12:03:14 GMT

Good job!