Let me preface this by saying that I am trying to learn more about large
scale BGP design and operation. This question is on route reflectors when
you have multiple POPs in seperate IGP domains. If you currently have one
POP and are going to move to 2 within the same AS, you can either run full
mesh (doesn't scale), reflectors, or confederations. Assuming you don't
currently have a central core that the POPs connect back to, how well does
reflection scale? I was reading Building Service Provider Networks
[Berkowitz], and it states that iBGP doesn't scale well once you go above
15-20 sessions per router. It also states that most ISPs run reflectors
instead of confederations, but I believe that statement is being made under
the assumption that the ISP will have a central core to which the POPs will
connect. This would indicate to me that assuming you don't have a central
core, one could only connect 6 or 7 POPs (dual reflectors for redundancy)
together using reflection before you would have to either create a central
core to reduce the amount of iBGP sessions, or turn to confederations.
Perhaps the best way to accomplish this would be to establish a "core" in
one of the POPs and run reflection from there, which is also presented as a
solution in the book? Any opinions? I have made an attempt at ASCII
drawing below, to me the central core solution makes more sense.
First Scenario, no central core
POP 1 POP 2
Cluster Cluster
o---------------o
Full Mesh Between Reflectors
o---------------o
Second Scenario, central core establised at one of the POPs
POP 1 POP 2
Core Reflectors
Clients o----- -----o Clients
o----- \ / -----o
o o
POP 3 / \ POP 4
Clients o----- -----o Clients
o----- -----o
Guy H. Lupi
CCIE No. 9275
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=48509&t=48509
--------------------------------------------------
FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html
Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
