Subject: TCP vs UDP

From: "Mareline Sheldon" <[email-masked]>
Date: Thu, 6 Sep 2001 17:25:46 +0530

Hi,
I have a very basic and an elementary doubt. Why is it that in RSVP we use
IP datagrams (or UDP at the margains of the network) and in CR-LDP we use
TCP ?
Making CR-LDP run over TCP makes it really vulnerable to all TCP attacks ...
why not run it over IP straightaway ?

Rgds
Mary

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From: "Mareline Sheldon" <[email-masked]>
Date: Thu, 6 Sep 2001 18:16:00 +0530

I think it is for this reason but i am not very sure ..
RSVP must periodically refresh the state of each LSP between adjacent nodes.
This allows RSVP to pick up changes to the routing tree automatically. Since
it uses IP datagrams as its transport , the control messages may be lost and
that an adjacent node may fail without notification. And this is why we use
state refreshes to keep them synchronized.

With some 10,000 LSPs on a link and a refresh period of 30s a very simple
calculation leads to the conclusion that this consumes 600kbits per second
of link bandwidth. This could be significant depending upon the link and
what this is as a fraction of the total traffic carried.

CR-LDP doesn't require refreshing of LSPs after the setup since it uses TCP.
It assumes relaible delivery of LABEL_REQUEST and LABEL_MAPPING messages.
Use of TCP adds no overhead to the data path and only 20 bytes to each
control message.

In order to maintain connectivity with adjacent nodes, CR-LDP uses HELLO
messages to check that the adjacent nodes are still active and KEEPALIVE
messages monitor the TCP connections. These relatively small messages are
exchanged periodically on the per *link* basis rather than the per *LSP*,
and so have virtually no impact on the throughput of the link.

Thus, CR-LDP presents lower load to the network than RSVP.

Even if RSVP BUNDLE messages are used then these will still be larger than a
single CR-LDP HELLO or KEEPALIVE.

So i guess running CR-LDP over TCP helps in a lower signalling load.

Moreover with running CR-LDP over TCP we dont require any explicit
authentication and policy control schemes.

Is all this correct ?

Regards,
Mary