Subject: Comment on draft-ietf-pwe3-control-protocol-03.txt section 5.4

From: Wei Luo <[email-masked]>
Date: Tue, 29 Jul 2003 10:12:12 -0700

In Section 5.4

     - Requested VLAN ID.

       An Optional 16 bit value indicating the requested VLAN ID. This
       parameter MAY be used by an PE that is incapable of rewriting the
       802.1Q ethernet VLAN tag on output. If the ingress PE receives
       this request it MAY rewrite the VLAN ID tag in input to match the
       requested VLAN ID. If this is not possible, and the VLAN ID does
       not already match configured ingress VLAN ID the PW should not be
       enabled.This parameter is applicable only to PW type 4.

What does "PW should not be enabled" mean exactly?  Unlike the MTU parameter
that both PEs send and verify it, only the egress PE that doesn't perform egress
VLAN rewrite sends this parameter.  Suppose the ingress PE is unable or
unwilling to honor ingress rewrite and both PEs have exchanged label bindings. 
Certainly, the ingress PE can keep the PW down in the data plane when it sees
this parameter.  However, from the egress PE's perspective, the PW is UP
(because it doesn't know whether the ingress PE accepts or rejects it) and it
will send traffic towards the ingress PE.  Therefore, packets are blackholed at
the ingress PE.  Not a big deal except a big waste of network bandwidth and
resource.

---Wei