From: Gary Duncanson (gary.duncanson@googlemail.com)
Date: Sun Aug 05 2007 - 08:45:18 ART
Hi Toh Soon,
You need routes to get to places. That's something I always bear in mind when
I do practice labs. You talk about eBGP peering not iBGP so Im not sure no
synchronisation is your issue.
You say you have full connectivity in IGP. This is not the case if you either
have no routes on R7 or a default route on R7 you can use for the networks you
are advertising in BGP.
From the looks of things R7 does not have the routes it needs to satisfy the
lab requirement of full IP connectivity.
So it needs to obtain them somehow.
Perhaps you have missed a redistribution point or a default route
advertisement somewhere in this lab?
Watch out for your next_hop on the routes in R8 as well. Have you considered
what an ebgp multihop solution may offer you?
Gary
----- Original Message -----
From: Toh Soon, Lim
To: Gary Duncanson
Cc: Djerk Geurts ; ccielab@groupstudy.com
Sent: Sunday, August 05, 2007 12:12 PM
Subject: Re: Is BGP full connectivity required?
Hi Gary,
One particular practice lab scenario I encountered is to configure eBGP
peering between two routers, say R5-R8. The session transits an intermediate
router, say R7, which does not run BGP. I already have full connectivity in
IGP. Elsewhere there's one AS that advertises few loopback addresses into BGP
which propagate to R8. Those loopbacks are not advertised in IGP.
The Advanced BGP section requires me to influence routing, set community,
etc. All done nicely. R8 has those routes in its BGP and IGP table, with
NEXT_HOP pointing to R5. To reach R5, R8 sends to R7. However R7 doesn't have
those BGP routes and therefore traffic is blackholed.
As I mentioned, it is stated at the beginning of the lab that upon
completion of this lab you should have full IP connectivity. But it's never
mentioned in BGP sections that we need to provide full connectivity for BGP.
What should I do?
Enjoy your QoS study :) I need to brush that up soon too.
Thank you.
B.Rgds,
Lim TS
On 8/5/07, Gary Duncanson <gary.duncanson@googlemail.com> wrote:
Many of the the practice labs I have worked on do not seem to provide
full
connectivity by IGP and redistribution alone. Once iBGP is introduced into
the mix full connectivity usually ensues. Of course you need to consider
no
synchronisation.
I would say assess pretty quickly if you *think* IGP and redistrib should
give you full connectivity and if you think not, press on with BGP etc and
try and get there. You can waste a lot of time in practice labs trying to
fix things that are not broken and trying to get things working that you
don't need or are already working or are going to work later in the lab.
This seems to be half of the game in lab prep, understanding the scenario
and what the technology should or shouldn't do for you given it's
operation,
it's dependencies of other protocols i.e iBGP and IGP, next-hop-self or
eBGP
and multihop, and the constraints you have to work with.
Anyway..it's a lovely sunny Sunday morning. Better study QoS now
*grumble*
;)
Gary
----- Original Message -----
From: "Djerk Geurts" < djerk@djerk.nl>
To: <ccielab@groupstudy.com>
Sent: Saturday, August 04, 2007 8:32 PM
Subject: RE: Is BGP full connectivity required?
> As a twist, say one is supposed to filter received routes so a few
routers
> do not have full visibility anymore. And the question doed not state
that
> this is ok (intentional, as it conflicts the ful connectivity
> 'directive').
> But BGP could reinstate connectivity...
>
> My take on the matter is: If in doubt check whether you've not missed
> anything and ask the proctor. (And don't ask open questions)
>
> But what is the general take here? Should IGP provide full connectivity
> and
> is BGP a bolt on (EGP only). Or is iBGP a valid substitute for the
> 'lacking'
> 'IGP' route distribution...
>
> Djerk
>
>> -----Original Message-----
>> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com ] On
>> Behalf Of Toh Soon, Lim
>> Sent: zaterdag 4 augustus 2007 10:24
>> To: ccielab@groupstudy.com
>> Subject: Is BGP full connectivity required?
>>
>> Hi All,
>>
>> Say, at the beginning of the lab it is stated that upon
>> completion of this
>> lab you should have full IP connectivity.
>>
>> I take it to mean full connectivity in IGP. Should I also consider
>> configuring full connectivity for BGP routes? However, it is
>> not mentioned
>> explicitly under the BGP section that we need to.
>>
>> Please advise.
>>
>>
>> Thank you.
>>
>> B.Rgds,
>> Lim TS
>>
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