Re: GEANT implementing "BGP Guard Time" on their Junipers (was: Route update stats)

[Pedro Roque Marques <]

Hannes Gredler writes:

> the root cause of the heavy bgp traffic you are observing is
> PR32066; JUNOS does trigger a duplicate eBGP message if there is an
> internal path change;

There is actually another workaround for PR32066 that may be useful to
some people:
  seting nexthop-self on the export policy facing ebgp.

This should be a NOP in terms of what the advertisements look like for
most people (i don't believe 3rd party nexthops are widely used).

<blush>
This bug is that, inadverly, a set of attributes that are relevant to
iBGP only (iBGP nexthop, cluster-list and confed segments) are taking
into account when comparing attributes for eBGP advertisements.

Thus, duplicate eBGP advertisements are not being suppressed correctly.
</blush>

Expanding on the issue of out-delay...

What out-delay does in JunOS, is to delay the advertisement of a route
for <interval> seconds since the actual route change...

This is very different from the cisco behaviour of advertisement
interval which specifies an <interval> between 2 distinct sets of
updates (by this it is ment 2 passes through the conceptual
RIB-OUT). Assuming that there is always some noise in the network
cisco's version of min-advertisement interval will in average delay an
update by <interval>/2.

So while both implementations take an <interval> in seconds, these
values actually mean something quite different. Using the same
absolute value on both implementations might not be what you want...

Also, you want to size up ebgp out-delay according to your iBGP
propagation times... a good heuristic for a single iBGP mesh is
probably 2 x <worse case>. The factor 2 is so that a iBGP withdrawl
can be propagated to the asbr w/ an alternate less prefered route and
that it has time to readvertise that route. <worse-case> is typically
verry dependent on your networking equipment... if you have ciscos
using their default configs, the iBGP min-advertisement time is often
used.

These guesstimates are provided without any warranty ;-)

  Pedro.