From: Christopher M. Heffner (cheffner@certified-labs.net)
Date: Tue Oct 22 2002 - 10:34:35 GMT-3
PU,
The sync/no sync rule applies to the prefix having to appear or not
appear in the IGP routing table before advertising the prefix to an
external BGP peer.
The sync rule does NOT apply to the next hop issue you are referencing.
The next hop of the prefix that is shown in the "show ip bgp" table must
to reachable according to the IGP table otherwise the prefix will NOT be
valid in the bgp table.
Remember the 3 rules for a prefix to be valid in the bgp table.
1. The can be no AS path loops in the AS Path attribute.
2. The prefix's advertised next-hop must be reachable by the IGP
routing table.
3. By default, the prefix must be in the IGP routing table in order to
be advertised to the external bgp peer unless all IBGP routers disable
synchronization with the "no sync" command.
Hope this helps.
Christopher M. Heffner, CCIE, CCSI
Strategic Network Solutions, Inc.
cheffner@certified-labs.net
-----Original Message-----
From: Prio Utomo [mailto:rionaldi@cbn.net.id]
Sent: Tuesday, October 22, 2002 6:20 AM
To: ccielab@groupstudy.com
Subject: BGP Sync Rule
Dear Experts,
I just want to confirm my understanding regarding the BGP Sync Rule, I
read
from Jeff Doyle that the rule said something like this
"prefixes learned IBGP will be put in the IGP routing table or forwarded
to
EBGP if only those prefixes available in the IGP Routing table", right ?
I tried to disable the syncronization on the border router but above
rule is
not applied... not until the next hope of those prefixes appear in the
IGP
routing table....
So my concusion was when sync disabled in the border router the next
hope of
the prefixes must be appear in the IGP routing table as well, for those
prefixes to be put in IGP routing table or forwarded to EBGP peer.
Regards,
PU
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