Subject: Re: RSVP hello message

From: "Hong Liao" <[email-masked]>
Date: Mon, 7 May 2001 22:01:04 -0400

David,

Thanks for your detail explanation for the RSVP tear down connection issue.

I still have one more for the Hello message needed to confirm.  Anytime,
the Ingress, Egress or LSR which supports Hello extension, will send out
Hello(request) message, for any reason the router which received this Hello
request message must first reply Hello ack back, then it can move to
another stage.

Suppose there is Ingress router which sends out Path message, it is waiting
Resv back from the Egress, but before it receives the Resv, it received a
Hello request message from neighbour, it must send out Hello ack back first
for any reason.

Thanks in an advance.
Julia

"Hong Liao" <[email-masked]> on 05/07/2001 02:37:23 PM

To:   David Charlap <[email-masked]>
cc:   [email-masked] (bcc: Hong Liao/Telcordia)
Subject:  Re: RSVP hello message

David,

Thanks for your pointer.  I really appreciated.

Did you get chance to take a look at my disconnection(clear network)
questions?

Thanks

Julia

David Charlap <[email-masked]> on 05/07/2001 12:23:10 PM

To:   [email-masked]
cc:    (bcc: Hong Liao/Telcordia)
Subject:  Re: RSVP hello message

Hong Liao wrote:
>
> The hello message in RSVP draft-ietf-mpls-rsvp-lsp-tunnel-07.txt, the
> format for hello message is as on section 5.1:
>
> <Hello message>:: = <Common Header>  [<INTEGRITY>] <HELLO>
>
> I want to make sure if the Hello object here is only one or a list
> of Hello objects.
> For my understanding, the format in Hello message, <Hello>  is not
> a list of Hello objects, it should be one Hello object between two
> RSVP neighbours.
> Can anyone help me to confirm this?

You have the correct understanding.  A single HELLO object per message.
One message per peer.  If for some reason you have multiple peers
sharing an interface (eg. a shared-media link), then each peer gets a
separate Hello message, each containing one HELLO object.

-- David

---

From: David Charlap <[email-masked]>
Date: Tue, 08 May 2001 13:11:42 -0400

Hong Liao wrote:
> 
> I still have one more for the Hello message needed to confirm.
> Anytime, the Ingress, Egress or LSR which supports Hello extension,
> will send out Hello(request) message, for any reason the router
> which received this Hello request message must first reply Hello
> ack back, then it can move to another stage.
> 
> Suppose there is Ingress router which sends out Path message, it is
> waiting Resv back from the Egress, but before it receives the Resv,
> it received a Hello request message from neighbour, it must send
> out Hello ack back first for any reason.

RSVP must not be run synchronously.

If a Path message is sent out, it MUST NOT block waiting for a Resv to
come back.  It may receive a thousand other Path messages before then,
and it can't block them all.

Since Hello messages are not dependant on any RSVP state, it should be
possible to handle them as they arrive, without regard for what other
messages may or may not have been received.

Keep in mind that if you delay responding to a Hello message, your
neighbor may decide that you have reset, tearing down all your
sessions.  If the draft's recommended interval/multiple for Hello is in
use, you will only have 17.5ms to get your response out.

-- David