BGP keepalive_time

[Arvin Gan]

Hi all,

   Anyone meet the issue as below reason that cause BGP hold timer timeout (keepalive_time > hold_time) and switch action between  closing and opening session?
Thanks
Arvin

From: Arvin Gan
Sent: Friday, June 08, 2018 3:22 PM
To: 'Ondrej Zajicek' <santiago at crfreenet.org>
Cc: bird-users at network.cz
Subject: BGP keepalive_time

Hi all,
     When I used bird, found a question that BGP session received OPEN message, hold_time is updated with min(config_hold_time, peer_hold_time), but keepalive_time is not updated if keepalive_time is not zero,  that maybe cause keepalive_time is more than  the updated hold_time after received OPEN message.

Line 702 in packets.cc for bgp protocol :
    conn->keepalive_time = p->cf->keepalive_time ? : conn->hold_time / 3;

  RFC 4271:
4.4. KEEPALIVE Message Format
BGP does not use any TCP-based, keep-alive mechanism to determine if
peers are reachable. Instead, KEEPALIVE messages are exchanged
between peers often enough not to cause the Hold Timer to expire. A
reasonable maximum time between KEEPALIVE messages would be one third
of the Hold Time interval. KEEPALIVE messages MUST NOT be sent more
frequently than one per second. An implementation MAY adjust the
rate at which it sends KEEPALIVE messages as a function of the Hold
Time interval.

Thanks
Arvin
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