Subject: [mpls] 答复: 答复: MPLS-RT review of draft-zjns-mpls-lsp-ping-relay-reply

From: Mach Chen <[email-masked]>
Date: Wed, 14 Nov 2012 08:42:40 +0000

Hi Ryan,

Sniped.

> 
> > b. it defines two types the relay address (IPv4, IPv6), does it
> > allow the combination of the two types (e.g., IPv4-IPv4-IPv6-IPv4)
> > in a single stack, if not, it should explicitly spell out. And if a
> > node support dual stacks, how does it decide which type should be used?
> <Ryan>The combination of IPv4 and IPv6 is allowed, that is why each relayed
> address in the stack has its own Address Type, either IPv4 or IPv6. Which type
> should be used depends on local configuration. Whatever IPv4 or IPv6, a
> routable address for other nodes is required here.

If combination is allowed, this may appear that a node only supports IPv4 but the stack includes IPv6 addresses, how does it handle this? Drop that entry may result in failing to relay the echo reply to the ingress. 

> 
> > c. the K bit, the draft said: "The K bit may be set by ASBRs which
> > address would be kept in the stack if necessary." How and when does
> > an ASBR know it should set the K bit? Can an non-ASBR set the K bit?
> <Ryan>It is under administrator control policy. It is recommended for the ASBR
> to set the K bit, but other node could also set the K bit.

IMHO, such definition may be difficult for implementation and operation. 

The K bit seems useless, it could just leave the authority whether to remove an entry to the node who is processing echo request, the rule is that only keep the least entries that can be used to relay the echo reply. 

For example:

Node2: 1, 2, 
Node3: 1, 3, since node 3 can directly sends echo reply to node 1, no need to keep 2;
Node4: 1, 3, 4, node 4 cannot directly sends echo reply to node 1, but node 3 is routable for it, so keep 3;
Node5: 1, 3, 5, node 3 is reachable for node 5, so no need to keep 4
...

Best regards,
Mach