[j-nsp] redistributing label between rsvp and ldp

[Keegan Holley]

I assumed you were exploring the configuration of the signaling protocols.
My point was that I can't think of a situation (not saying that one doesn't
exist) where I would run both protocols on purpose. At most it would happen
during a cutover from one to the other.  I can't think of many things one
protocol does that the other doesn't that are important enough to keep both
around permanently.

Also, I thought BGP signaling still depended on RSVP or LDP to advertise
the outer labels.  I would assume this is the case for any method that uses
BGP signalling because there is no way to map a BGP advertisement to a
particular interface and labels are only locally significant.  I'm not an
expert though.


I haven't done much research either but here's an excerpt from the RFC I
found:


2. Transport IPv6 packets from the ingress 6PE router to the egress
      6PE router over IPv4-signaled LSPs:

      The ingress 6PE router MUST forward IPv6 data over the IPv4-
      signaled LSP towards the egress 6PE router identified by the IPv4
      address advertised in the IPv4-mapped IPv6 address of the BGP Next
      Hop for the corresponding IPv6 prefix.


3.  Transport over IPv4-signaled LSPs and IPv6 Label Binding

   In this approach, the IPv4-mapped IPv6 addresses allow a 6PE router
   that has to forward an IPv6 packet to automatically determine the
   IPv4-signaled LSP to use for a particular IPv6 destination by looking
   at the MP-BGP routing information.

   The IPv4-signaled LSPs can be established using any existing
   technique for label setup [RFC3031] (LDP, RSVP-TE, etc.).

   To ensure interoperability among systems that implement the 6PE
   approach described in this document, all such systems MUST support
   tunneling using IPv4-signaled MPLS LSPs established by LDP [RFC3036].

   When tunneling IPv6 packets over the IPv4 MPLS backbone, rather than
   successively prepend an IPv4 header and then perform label imposition
 When tunneling IPv6 packets over the IPv4 MPLS backbone, rather than
   successively prepend an IPv4 header and then perform label imposition
   based on the IPv4 header, the ingress 6PE Router MUST directly
   perform label imposition of the IPv6 header without prepending any
   IPv4 header.  The (outer) label imposed MUST correspond to the IPv4-
   signaled LSP starting on the ingress 6PE Router and ending on the
   egress 6PE Router.

http://www.ietf.org/rfc/rfc4798.txt


2012/4/30 Uzi Be <good1 at live.com>

>  Hi Keegan,
>
> Thanks for your reply and explaining all the caveats of mpls signaling
> protocols. First of all, I am not gonna use this kind of setup in
> real environment. I am doing all of this in order to learn how to integrate
> two different labeling protocols in various circumstances.
>
> I don't wana run same signaling protocol on the PEs, so PE1 will run LDP
> and PE2 will run RSVP. Since PE2 is not gonna run LDP at all,  so I can't
> use ldp-tunneling here either. I could have use bgp labeled on top of ldp
> and rsvp but was wondering if there are any other workarounds.
>
> Second, will it work for 6pe if you use bpg labeled mpls signaled path as
> an next-hop for 6pe.
>
> Thanks
> Andrew
>
> ------------------------------
> From: keegan.holley at sungard.com
> Date: Sun, 29 Apr 2012 18:56:53 -0400
>
> Subject: Re: [j-nsp] redistributing label between rsvp and ldp
> To: good1 at live.com
> CC: juniper-nsp at puck.nether.net
>
>
> Labels aren't like routes per se.  They only point to a next hop and not a
> destination so you don't have to exchange labels between two routing
> protocols in the same way you would routes.  You only have to configure the
> routers at the edge of each topology so that it runs both protocols.  That
> being said RSVP adds a caveat.  If you try to form a RSVP LSP that
> traverses a router that isn't running RSVP it will either fail to form or
> re-route.
>
> LDP does not have this constraint and just advertises labels to directly
> connected peers.  To bridge between the two protocols I would configure p3
> (and every router at the edge of your RSVP domain) as a PE running both LDP
> and RSVP.  You can terminate the RSVP LSP's there.  Since it's a PE it
> should be able to match the L3VPN information advertised by pe2 via BGP
> with the LDP labels it's advertising.
>
> You could also turn on LDP on all of your routers.  Any IP that doesn't
> have an RSVP next hop failover to LDP and vise versa.  This is easier to
> manage since it will be obvious which paths use LDP and which ones use
> RSVP.  The ultimate solution is probably to run only one label protocol
> though.
>
>
>
> 2012/4/29 Uzi Be <good1 at live.com>
>
>
> hi,
> I was just testing out to swap labels between two different signaling
> protocols (ldp and rsvp). lets say we have two different network, one is
> running ldp and the other one is running rsvp (same AS, so no inter-as
> options).
> ce - pe1 - p1 - p2 - p3 -p4 -pe2 - ce
> so pe1 - p1 - p2 -p3 are running rsvp and p4-pe2 are running ldp, and edge
> ce's are using l3vpn. what are the options to have a labeled path from pe2
> to pe1 (considering that pe1 is not going to run ldp protocol, and pe2
> can't use rsvp so ldp tunneling is not an option here).
> thanks in advance for your comments.
> Andrew
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