From: Eric Phillips (ephillips@squick.cc)
Date: Thu Nov 29 2007 - 13:31:04 ART
Hey all,
I am seeing a really strange outcome when I combine BGP synchronization and
confederations. I have not been able to find an answer to what I am seeing
because every book I refer to just says to turn synchronization off.
Assume I have four routers configured in a row:
R1 -- R2 -- R3 -- R4
R1 is in AS 100 and has a lot of routes it is advertising.
R2-R4 are in AS 200, which is also a confederation.
R2 is in AS 65502
R3 and 4 are in AS 65501.
Each router peers only with its neighbor.
AS 200 also has synchronization enabled in it.
As expected, nearly all routes on R4 are in the BGP table, but not selected
as best, and not put in the routing table.
The strange behavior I am seeing is R3 has all of the routes coming from R1
and R2 marked as best and in the routing table, but with an AD of 200
(IBGP). But as expected, the advertised loopbacks from R4 are not marked
best because they were learned via IBGP. So it appears synchronization is
treating them like EBGP routes, but they have the AD of IBGP routes.
So my question is, does BGP synchronization think that since the routes were
learned from another AS within the confederation that they are EBGP routes
and install them even though no other routing protocol has advertised them?
If so, that would make it possible to basically circumvent synchronization
if you made every router it's own sub-AS within a confederation, right? And
as a slight formality, the link between R2 and R3 is considered EBGP,
right? So if a question said "do not use EBGP" that would rule
confederations out; right?
Thanks,
Eric
This archive was generated by hypermail 2.1.4 : Sat Dec 01 2007 - 06:37:32 ART