Subject: Queries regarding RFC 3032

From: "George Thomas" <[email-masked]>
Date: 15 Apr 2002 09:35:19 -0000

hi,

I have two queries regarding MPLS Label Encapsulation.
can someone answer these.

1. If there is no LSP associated with a destination 
(Unicast/Multicast), whether it is mandatory to use NULL Label 
Encapsulation, and encoding the ethertype value to 
0x8847/0x8848.
    or Is it valid to send as Native IP packet with Ethertype 
value as 0x800 in the MPLS network.

2. If NULL label is Mandatory, for a broadcast packet, what 
ethertype value should be used? Whether the Mulitcast ethertype 
value can be used?

If NULL label is not mandatory, it implies that any native IP 
packet can be sent with ethertype value as 0x800 in a MPLS domain 
without Label encapsulation. Am i right?

Regards
George

---

From: David Charlap <[email-masked]>
Date: Mon, 15 Apr 2002 10:51:26 -0400

George Thomas wrote:
> 
> 1. If there is no LSP associated with a destination (Unicast/
>    Multicast), whether it is mandatory to use NULL Label
> Encapsulation, and encoding the ethertype value to 0x8847/0x8848.

If an LER receives an unlabeled packet, and there is no forwarding table
information descrbing what LSP to send the packet on, then the behavior
is beyond the scope of MPLS.

It would be legal to forward the packet hop-by-hop, as a non-MPLS router
would.  It would also be legal to drop the packet and generate an ICMP
error (treating it as a non-MPLS router would if there is no route to
the destination.)

I would not expect a NULL label to be used in this situation.

> without Label encapsulation. Am i right?

MPLS routers have to be able to send and receive non-labeled packets. 
That's how the routing and signaling protocols all work.  Whether they
also have the capability of forwarding unlabeled packets is up to the
design of the router, of course.  I think such capability is required
for some protocol features (like extended-discovery LDP peering),
however.

Of course, Ethertypes are only valid on those interfaces that use
Ethertypes.  Other interfaces would use whatever layer-2 types are
appropriate for the IP packet.

-- David