From: OhioHondo (ohiohondo@columbus.rr.com)
Date: Tue Apr 15 2003 - 14:32:14 GMT-3
Howard
Thank you for your reply. Since your answer indicates a single IGP domain
for a sub-AS or a non-confederated AS, I have a followup if I may. Assume
OSPF as the IGP.
If I have an AS or a sub-AS that consists of several routers running EBGP to
sevaral external AS's and sub-AS's --- and running IBGP of course, what is a
scenario where synchronization works without causing problems??
Within a sub-AS or non-confederated AS you would run a full mesh or route
reflection. In simple scenario's the concept of synchronization is easily
explained, but when I lab it up in a larger environment -- synchronization
(along with the only propagate the Best Route rule, interferes with the
coordinated effort of the IBGP routers to establish a common policy.
An example --- setting the Local Preference on routes received from external
AS's or sub-AS's. If rtrA learns a route via EBGP and installs it in its' IP
routing table, and rtrB learns the same route but gives it a higher Local
Preference, the route from rtrB will not be synchronized at rtrA or any
route-reflector clients of rtrA.
I would consider this a problem. Is there a workaround???
I've read comments in books that state synchronization should not be used
with full mesh or RR. (Note that if each sub-AS in a confederation has its'
own IGP domain, there are no other options.) What's the story??? ;)
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Howard C. Berkowitz
Sent: Monday, April 14, 2003 10:28 PM
To: Group Study
Subject: Re: BGP in Confederations and Using Synchronization
At 8:58 PM -0400 4/14/03, OhioHondo wrote:
>Hello
>>
> I thought I'd try resending this because the orginal thread
>got somewhat
>off track. Someone suggested that, when using confederations, each sub-AS
>should be its' own IGP domain (i.e. with OSPF, have it's own area 0) Does
>everyone else agree with this??
Emphatically agree. The whole point of confederations is to bound a
community of interest, with the reduction of iBGP loads in comparison
with non-confederation a desirable side effect. If you are trying to
bound BGP information, what would be the point of leaking IGP
information outside the community of interest?
*sigh* I suppose I can't preclude something like this on a lab, given
Cisco's propensity for wanting to explore knowledge of knobs with
configurations which, if anybody did in the real world, should be
grounds for firing. But from my perspective, it really makes sense
to master the plausible configurations first, and learn the protocols
in the way they were intended to be used. If you get sufficient
understanding of this and then get a weird case in the lab, your
in-depth understanding should dig you out. It's simply not possible
to practice every conceivable permutation of protocol options,
especially those that don't make sense.
>
>Thge original question was....
>I have a question for someone with a grasp on BGP Confederations and how>
>synchronization affects it. My scenario
>>
>> AS301/R7 --- AS501/sub-AS65001/R3 --- AS501/sub-AS65002/R1 --- AS101/R9
>> |
>> |
>> AS501/subAS65001/R2
>>
>> Routers R1, R2 and R3 are in a single OSPF domain. The BGP router-id's
and
>> OSPF router-ids are the same on all routers.
>>
>> My problem --- an advertisement comes in from AS101/R9, let say
>49.0.0.0/8.
>> That advertisement is propagated via OSPF to router R2 with R1's OSPF
>> router-id.
>>
>> When that advertisement crosses the sub-AS border between R1 and R3, the
>BGP
>> router-id is changed to that of R3, therefor when the iBGP route gets to
>R2,
>> the BGP router-id is from R3 while the OSPF router-id is from R1. The
>result
>> is no sync. Any advice????
>
>Jerry Haverkos
>jhaverkos@columbus.rr.com
>614-351-8617
This archive was generated by hypermail 2.1.4 : Thu May 01 2003 - 13:35:53 GMT-3