The MPLS WG Archive

[Ping Pan <pingpan@juniper.net>]

Ken Nagami wrote:
> 
> Hi Ping,
> 
> >> You don't give a message type for the LSP-ping.  Were you thinking of
> >> a new message?  Perhaps the Notify message could be used?
> >>
> 
> >> For LSP-ping messages, the echo packets are encapsulated in UDP with a
> >> well-known port number. At the egress, the LSR picks up the echo by
> >> "listening" to the UDP port, and replies them back in Resv. I didn't
> >> consider the Notify message.... Let me think about it.
> 
> Why do you use a RSVP RESV message for an LSP-ping reply?
> I think it is better to use an UDP packet which is the same as
> LSP-ping echo message. If you don't use an MPLS control
> message(RSVP-TE, LDP) for the LSP-ping, this mechanism can be used for
> all kind of LSP, such as a static LSP and an LSP established by LDP.
> 

Ken,

LSP-ping is used to probe the data path. There are cases where the data
path goes wrong, and you have no idea where the problem is (forwarding
LSP, reverse LSP, ...). Since the only operational path that you can
count is the control path, so you reply via RSVP.

If you use UDP to return the reply, what if the returning path is
broken? Should the user assumes the forwarding LSP is bad, or the
reverse?

At the same time, if you can come up with a simple, scalable, backward
compatible method to use for LDP (including the case where you can label
merging) as well, please do let us know. :-)

- Ping