tree 89db8427d6133250d80e20b00a6d9b209c7933a9
parent a2f0db2be27385211f033271d8b83e9caf362236
author Paul Jakma <paul.jakma@hpe.com> 1463488096 +0100
committer Paul Jakma <paul@quagga.net> 1485197519 +0000

bgpd: Modernise BGP defaults for MRAI and connect time

Quagga uses historic BGP defaults for its minimum route advertisement
interval (MRAI) timers, and its ConnectRetry timer.  It uses 30s and
5s for the eBGP and iBGP MRAIs, and 120s for the ConnectRetry timer.
These values are quite high, and delay convergence and session
establishment, and are unlikely to be desirable in modern networks.

The MRAI can, without a doubt, be significantly reduced.  The optimal
MRAI is related to the size of the network, its diameter in terms of
BGP propagation latency particularly.  Prior research suggests values
of 5s to 15s for Internet BGP, as reasonably conservative values.
Further, other implementations have long shipped with 1s or even 0s
MRAI values.

A too low MRAI, e.g.  a 0 MRAI, can greatly increase the number of
BGP messages a speaker sends, and hence the bandwidth and even CPU it
might use.  I.e.  some MRAI is better than no MRAI, with current BGP,
or it is prone to excessive - even extreme - chattiness.

The ConnectRetry timer default also should be set much lower.

Lowering the MRAI had previously been suggested by:

   "Lower the default MRAI timer for iBGP peers to 0

    Signed-off-by: Daniel Walton <dwalton@cumulusnetworks.com>
    Reviewed-by:   Donald Sharp <sharpd@cumulusnetworks.com>"

* bgpd/bgpd.h: Set defaults to:
  - 3s for the eBGP MRAI
  - 1s for iBGP MRAI (lower, but non-0, would be nice for this)
  - 5s for the ConnectRetry timer