So we've been discussing this on Slack. It seems the packet handlers for IS-IS in FRR and how they work on FreeBSD is not completely optimized (not an issue on Linux).
FRR-based IS-IS on FreeBSD is sending PSNP's that are 6,020 bytes large. However, FreeBSD's BPF (Berkeley Packet Filter) has a packet data limit of 4,096 bytes. This is what is causing the error. While it is possible to set the IIH MTU in FRR with the "lsp-mtu" command, there is not way to set the PSNP MTU. In short, IS-IS on FRR does not understand that there is an MTU limit for PSNP's on FreeBSD. I'm working with the IS-IS FRR team, but as of now, no idea on if/when there will be a fix for this. While routes are being successfully exchanged between FRR and Cisco IOS XE for IS-IS, this is a show-stopper! So for the moment, I cannot recommend anyone runs IS-IS on FRR in production. As it stands, it appears that this is the only thing standing in the way of a successful deployment, as far as simple Anycast services go. Will keep you all posted as this develops. Mark. On 18/Apr/20 16:34, Tony Li wrote: > > No, IIH’s are padded, hot PSNP’s. > > Tony > >> On Apr 18, 2020, at 3:08 AM, [email protected] wrote: >> >> >> >> Just shooting in the dark, Isn’t the PSNP padded to some ISIS defined >> max MTU and that somehow fails due to mismatch on em0 L2 MTU? >> >> >> >> adam >> >> *From:*NANOG <[email protected]> *On Behalf Of *Mark Tinka >> *Sent:* Friday, April 17, 2020 11:05 AM >> *To:* [email protected] >> *Subject:* IS-IS Error (FRR) >> >> >> >> Hi all. >> >> I'm almost there getting IS-IS to work without issue. I'm now faced >> with the following error log: >> >> 2020/04/17 10:02:01 ISIS: IS-IS bpf: could not transmit packet on >> em0: Input/output error >> 2020/04/17 10:02:01 ISIS: [EC 67108865] ISIS-Snp (1): Send L2 PSNP on >> em0 failed >> >> This repeats every second. >> >> Anyone know what this could be? >> >> Systems is FreeBSD-12.1-RELEASE-p3. >> >> Despite the error, IS-IS is running and routing is good, talking to a >> Cisco IOS XE implementation on the other side. So the error is >> throwing me off. >> >> No feedback from the Slack feed, Google doesn't say much, and waiting >> to hear back from the FRR list. >> >> Mark. >>
