[FROG] What causes a prefix received from a downstream to be "invalid"?

Novak, Jan jan.novak at intl.att.com
Mon Nov 9 10:00:58 UTC 2020


Hi,
There has to be something in the RIB covering the next hop

2a0d:f300:0:VVVV::1 (inaccessible)

For BGP to install the prefix into the RIB - that's the first check BGP does for
Validity of a prefix ...

Jan



-----Original Message-----
From: frog <frog-bounces at lists.frrouting.org> On Behalf Of Michael Hohl
Sent: 09 November 2020 08:46
To: frog at lists.frrouting.org
Subject: [FROG] What causes a prefix received from a downstream to be "invalid"?

Hello FRRouting community,

I've tried to add an IPv6-only downstream to my dual-stack FRRouting-powered BGP setup, but for some reason the prefix of that downstream wasn't distributed to my upstream ISP. So, I consulted `show bgp summary` and spotted that this is the only route which isn't marked as `valid` indicated by a `*`. RPKI isn't enabled, otherwise I would have immediately suspected that to cause some prefix to be invalid. The only thing that makes this downstream different is that it is IPv6-only.

What does it mean that a (received) prefix is considered "invalid"?

Here is the output for `show bgp 2001:XX:YY::`:

```
BGP routing table entry for 2001:XX:YY::/48
Paths: (1 available, no best path)
  Not advertised to any peer
  ZZZZZZ
    2a0d:f300:0:VVVV::1 (inaccessible) from 2a0d:f300:0:VVVV::1 (193.219.VV.VV)
      Origin IGP, invalid, external
      Last update: Mon Nov  9 09:00:00 2020 ```

ZZZZZZ              ... is the downstreams ASN
2001:XX:YY::        ... is the IPv6 prefix the downstream wants to announce
2a0d:f300:0:VVVV::1 ... is the IPv6 address used to run the BGP router of the 
                        downstream
193.219.VV.VV       ... is the IPv4 address assigned by me to the downstream, 
                        but he doesn't really use that one

In case the FRRouting version is relevant for this issue, I'm running 7.3.1.

Thanks in advance for any help,
Michael



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