BIRD drops specific IPv6 session for no reason

[Stavros Konstantaras]

Hi Ondrej,

Great feedback, thank’s a lot for sharing it with us. Currently we are using the kernel 3.16.39-1+deb8u2, do you remember if this kernel was inside the list of complains? 

We will schedule a maintenance to update the kernel in both Route Servers and see if that solves the issue. 

Thank you for the “debug” tip as well, I wasn’t aware that gives you that much detailed output like sending Keepalives to a peer. I will give it a shot. 



Best regards,

Stavros Konstantaras | Sr. Network Engineer | AMS-IX 
M +31 (0) 620 89 51 04 | T +31 20 305 8999
ams-ix.net

> On 28 Feb 2020, at 16:42, Ondrej Zajicek <santiago at crfreenet.org> wrote:
> 
> On Fri, Feb 28, 2020 at 03:33:06PM +0100, Stavros Konstantaras wrote:
>> HI Alarig, 
>> 
>> Thank you for sharing your experiences. I don’t have the MSS currently but if that was the case, wouldn’t have experienced the drops more frequently?
>> Currently it happens once per month (or 0.8 per month) and contrary to your case which was 100% network related, in our case we don’t even see the
>> reply packet being generated and leaving the box. 
>> 
>> What puzzles me also and based on the capture, is that I don’t see the TCP-ACK messages being sent to the customer. If BIRD opens a TCP socket 
>> (not a simple RAW socket), I assume that the TCP connection will be handled by the OS and BIRD will push data segments (BGP keep alive messages) when ready.
>> 
>> But as per output, I don’t see the TCP ack messages at all. Is BIRD handling the TCP communication as well? 
> 
> Hi
> 
> That is a good point. BIRD uses regular TCP socket, so if you do not see
> TCP ack, then it is likely an underlying (kernel) issue. There were some
> reports of IPv6 issues in recent kernels [*]
> 
> Also, the log message:
> 
> Feb 20 21:46:11 rs1-mng bird6: 2001:7F8:1::A500:19:7727:1: Received: Hold timer expired 
> 
> shows that the notification message was received by the BIRD. The packet
> dump shows that keepalives were not sent by BIRD side. You could enable
> 'debug all' for given peer to see if BIRD tries to send keepalives. You
> could also monitor state of socket using 'ss' tool.
> 
> [*] https://bird.network.cz/pipermail/bird-users/2020-February/014270.html
> 
> -- 
> Elen sila lumenn' omentielvo
> 
> Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
> OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
> "To err is human -- to blame it on a computer is even more so."

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