Comments inline
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On 8/8/2001 at 2:48 PM Ole Drews Jensen wrote:
>Thanks Peter.
>
>I have browsed through Howards's BGP series, but for me, sometimes too long
>explanations are more frustrating than a 10 words fact.
>
>Two additional questions if you don't mind, and you have a minute or two
>:-)
>
>1)
>
>If you only have one BGP connection to one remote AS, IBGP would normally
>never be used, and you would in most cases create a static default route to
>the BGP router and redistribute it in your IGP. Am I right?
>
You are very correct and this is a typical use of default routing. IBGP by
definition has no place here as it is a protocol used between BGP peers in
the same AS and if you have only only router in the AS, nothing matches that
criteria.
>2)
>
>Should you have multiple BGP routers in the AS connected to two different
>remote AS's - would I always configure IBGP between them, or would there be
>situations where IBGP would still be unused?
Keep in mind that IBGP distributes BGP learned routing information among
peering routers within an AS. Hence, if you want border routers A and B to
be aware of each others upstream connectivity, IBGP is your tool. Should
you be providing transit, that is to say you are advertising that you can
forward packets to destinations not originating in your AS, you will
definitely require this functionality. Without it, A may advertise
reachability to networks downstream of B that B, or other routers in the
transit path from A to B do not know about. In this case you would
blackhole those routes.
In non transit AS's, your level of use of BGP can vary. If you have
multiple providers and some redundancy in the way of multiple BGP speaking
routers inside your AS, you could achieve gains in least cost forwarding by
using IBGP to ensure all BGP speakers had the most accurate reachability
information. It's really a balance here between how badly you need traffic
to take the most optimal path out of your network and much you want to spend
on infrastructure. Default routing is an excellent tool :)
>Thanks again,
>
>Ole
>
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Ole Drews Jensen
> Systems Network Manager
> CCNA, MCSE, MCP+I
> RWR Enterprises, Inc.
> [EMAIL PROTECTED]
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> http://www.RouterChief.com
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> NEED A JOB ???
> http://www.oledrews.com/job
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
>
>-----Original Message-----
>From: Peter Van Oene [mailto:[EMAIL PROTECTED]]
>Sent: Wednesday, August 08, 2001 2:38 PM
>To: Ole Drews Jensen; [EMAIL PROTECTED]
>Subject: Re: BGP: IBGP usage/clarification [7:15333]
>
>
>A couple quick notes. However I would suggest if you have a subscription
>that you step through Howards BGP series at www.certificationzone.com as it
>might help you solidify your understanding.
>
>First off, IBGP is not an IGP. If you want to get from point A to point B
>in AS C, IBGP isn't your friend (unless operator X tweaked IBGP with lots
>of
>messiness -ie NHS everywhere etc....) IBGP facilitates inter-AS routing by
>enabling reachability information to be maintained within AS's. IGP are
>still required to enable routing within the AS (ie intra-AS routing).
>
>IBGP is used when you have multiple BGP routers in an AS. Really not much
>more to it than that at a high level. Whether or not you chose to use a
>dynamic IGP versus a static configuration really is up to the administrator
>with typical pros/cons applying. I have seen some cases where stub AS's
>(those not providing transit) may have border routers communicating via BGP
>to ISP's without peering amongst themselves but these are pretty unique
>(weird) situations which often beg the question why BGP in the first place,
>but this would be an fruitless digression.
>
>Pete
>
>
>*********** REPLY SEPARATOR ***********
>
>On 8/8/2001 at 3:06 PM Ole Drews Jensen wrote:
>
>>This might sound like a stupid question, but I have now read and
>>practised a
>>lot of BGP stuff, but there's one thing I am not 100% sure I understand;
>>None of the books have been able to put the last brick in place in the
>>puzzle for me.
>>
>>In what situations will "end-user" companies use IBGP and not just an IGP
>>as
>>OSPF or EIGRP?
>>
>>I believe that most ISP's use IBGP with a full mess where there are more
>>than one EBGP connection - right?
>>
>>And a question to those of you who do a lot of BGP setup's for customers,
>>how often do you typically use BGP at "end-user" companies and how often
>>will IBGP be used there with or without an IGR running on their
>network(s)?
>>
>>Thanks for any comments on this,
>>
>>Ole
>>
>>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> Ole Drews Jensen
>> Systems Network Manager
>> CCNA, MCSE, MCP+I
>> RWR Enterprises, Inc.
>> [EMAIL PROTECTED]
>>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> http://www.RouterChief.com
>>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> NEED A JOB ???
>> http://www.oledrews.com/job
>>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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