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Do Control packes use LSP?

  • From: "Alexander Marhold" <alexander@marhold.at>
  • Date: Tue, 19 Jun 2001 09:52:25 +0200
  • Cc: <mpls-ops@mplsrc.com>, <mpls@UU.NET>
  • Importance: Normal

----> see inline answers

Do the control packets originated by an LSP ingress,
directed toward the LSP egress router use MPLS
forwarding?  By control packets, I mean any protocol
packets originated by layer 3 on the ingress.

---> Yes, details seee below

Consider the following scenario:-

    Router A -----[ IP/MPLS cloud ]----- Router B

Assume that the above network is one AS.  Routers A,
B and all routers in the cloud run OSPF.  An LSP is
setup between A and B and another one is setup in the
reverse direction.  Traffic engineering is enabled at
A as well as at B.

Now, I found no reference in any MPLS draft/RFC which
talks about forwarding packets originated at router A,
destined for router B.  Are these packets forwarded
using MPLS or using "normal" IP routing?

---> they are treated like any packet with a given destination address and
in that they will use the LSP

I assume (because it sounds logical - though I did not
see any mention of it in documents), that the
signaling packets for the LSP itself (say refresh
messages in RSVP) shall not be sent over the LSP.

---> RSVP is sent HOP-by-HOP so the destination address is always the
physical next-hop
so in a typicall framebased implementation using PHP (penultimate hop
popping) they are sent unlabelled

I am not sure about sending other protocol packets.
Say, A and B also run I-BGP with each other as the
peer.  Do the BGP (or any other application) packets
use LSP?

---> YES, they are treated like any L3 packet and are using by default the
same FORWARDING engine like other packets

I say "by default", as there maybe could be vendor implementations treating
local packets differently, even though I am currently not aware of such
implementation

with best regards

Alexander

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