From: Howard C. Berkowitz (hcb@xxxxxxxxxxxx)
Date: Sun May 26 2002 - 19:23:50 GMT-3
At 10:31 PM +0800 5/26/02, eric ong wrote:
>Sorry, I should have given more info:
>
>x.x.x.x -- R1(AS1) -- R2 --- R3(AS3)
> / \
> (AS2)R4 R5(AS2)
>
>- R2 is non-BGP
>- R1 ebgp peers to R4
>- R3 ebgp peers to R5
>- R4 ibgp peers to R5
>- R1 does 'network x.x.x.x'
>- no sync on all
>- IGP connectivity throughout (except for x.x.x.x)
>
>If x.x.x.x doesn't go into IGP (via network or distribute), all BGP
>routers will have x.x.x.x in their routing tables, but will not be
>able to ping it as R2 (non-BGP) will not know about x.x.x.x.
>
>So my question is: given that the requirement only states to
>advertise x.x.x.x through BGP, must x.x.x.x be pingable from BGP
>routers or from all routers (including non-BGP) or it doesn't have to
>be pingable at all?
It's not the greatest of question phrasing, but, at the very least,
the address must be reachable. One of the loop prevention rules of
BGP is that a router MUST NOT advertise a route to which it is unable
to route. So, the originating router must be able to reach it. As a
consequence, any BGP peer should see the address and be able to ping
it.
As you suggest, R2 would not be able to ping it. It's entirely
possible that the other routers could not get the ping response,
unless R2 had a default router or an IGP relationship with R1.
It's a somewhat strange configuration for standard BGP, but it does
relate to BGP/MPLS (RFC 2547) where there would be MPLS paths through
R2 for all the BGP peerings, and R2 would be an RFC 2547 "P router".
>
>
>eric ong
>
>
> --- Oliver Boehmer <oboehmer@cisco.com> wrote: >
>> My guess is to assign the IP address (range) to an interface
>> (loopback?) and advertise it using "network x.x.x.x" via BGP. So
>> you can ping it from BGP routers.. It doesn't say anything about
>> advertising it via IGP..
>>
>> oli
>>
>> At 19:30 26.05.2002 +0800, eric ong wrote:
>> >Qn: On R1, assign and advertise x.x.x.x through BGP.
>> >
>> >x.x.x.x is not being advertised by any other protocols.
>> >
>> >So what is this question asking for?
>> >
>> >Just make x.x.x.x appear in all BGP routers' BGP table, don't care
>> if
>> >it's pingable?
>> >
>> >Or must the whole network (non-BGP routers too) be able to ping
>> >x.x.x.x?
>> >
>> >If it's the latter, can I advertise x.x.x.x through IGP or must I
>> >redistribute BGP into IGP on R1?
>
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