Re: MPLS forwarding in partial mesh frame-relay networks

Bryan,

Yes that makes sense. I just couldn't see what effect the targeted
LDP session might have had in this scenario even if you had some VPN
label exchange between R2 and R3.

-Rich

On Fri, Jan 22, 2010 at 4:49 PM, Bryan Bartik <bbartik_at_ipexpert.com> wrote:
> Rich,
>
> I am not sure why there is a targeted session there. I don't see how
> targeted would fix it. Because (using Steve's example), if R2 had an LDP
> session to R3 and then could use the label that R3 advertised, it would be a
> pop-label...not the label advertised by R1. Therefore, the inner (VPN) label
> still gets exposed to R1 as the packet gets forwarded. Does that explain it?
>
> On Fri, Jan 22, 2010 at 2:44 PM, Rich Collins <nilsi2002_at_gmail.com> wrote:
>>
>> Hi Bryan,
>>
>> Thanks for that clarification.
>>
>> I was wondering if or how the "targeted LDP sessions (between B&C)"
>> come into play in this scenario?
>>
>> -Rich
>>
>>
>>
>> > On Sat, Jan 23, 2010 at 12:08 AM, Bryan Bartik <bbartik_at_ipexpert.com>
>> > wrote:
>> >>
>> >> Cool. In case you are wondering how the router might know the next-hop
>> >> address belongs to the downstream LSR...it is contained in an address
>> >> mapping message. The LSR basically sends all its interfaces addresses,
>> >> so
>> >> the peer can look them up and tell if it can install the label or not.
>> >> If
>> >> you do a "show mpls ldp neighor" at the bottom you will see a section
>> >> called
>> >> "Addresses bound to peer LDP Ident:"
>> >>
>> >> On Fri, Jan 22, 2010 at 11:31 AM, Divin Mathew John
>> >> <divinjohn_at_gmail.com>
>> >> wrote:
>> >>>
>> >>> Oh.! Thats was something !
>> >>>
>> >>> On Fri, Jan 22, 2010 at 11:56 PM, Steve Shaw <shaw38_at_gmail.com> wrote:
>> >>>>
>> >>>> Bryan,
>> >>>>
>> >>>> Thanks! That's the rule I was looking for.
>> >>>>
>> >>>> Steve
>> >>>>
>> >>>> On Fri, Jan 22, 2010 at 1:03 PM, Bryan Bartik <bbartik_at_ipexpert.com>
>> >>>> wrote:
>> >>>>
>> >>>> > Rich,
>> >>>> >
>> >>>> > An LSR will only install a label for a prefix if the next-hop for
>> >>>> > that
>> >>>> > prefix is an address that belongs to the router from which it
>> >>>> > learned
>> >>>> > the
>> >>>> > label. So if Router B's next-hop for Router C is Router C's
>> >>>> > address,
>> >>>> > it will
>> >>>> > not install the label because the label was learned from Router A.
>> >>>> >
>> >>>> > What you can do to fix this is install a static route on router B
>> >>>> > for
>> >>>> > C's
>> >>>> > address that points to A as the next-hop. Now the label learned
>> >>>> > from A
>> >>>> > will
>> >>>> > be installed.
>> >>>> >
>
>
>
> --
> Bryan Bartik
> CCIE #23707 (R&S, SP), CCNP
> Sr. Support Engineer - IPexpert, Inc.
> URL: http://www.IPexpert.com

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Received on Fri Jan 22 2010 - 17:42:05 ART