Subject: Checksum in RSVP messages

From: Roberto Guglielmi <[email-masked]>
Date: Wed, 04 Apr 2001 10:28:20 +0200

Hi all,
I have a couple of questions about calculating RSVP checksum in the
common header.

Our SW product implementing RSVP calculates the checksum making the
one's complement of sum two-by-two of the bytes contained in the
messages.
The problem is that using the Sniffer protocol analizer to decode the
messages sent by the nodes, the checksum seems to be wrong.

The RFC 2205 says the checksum is calculated in the following way:

         "The one's complement of the one's complement sum of the
message , with the checksum field replaced by
            zero..."

Are the bytes within the message supposed to be added one-by-one or
two-by-two?

Are we supposed to make the one's complement of the message, make the
sum and, at the end, the one's complement of the sum?

I would appreciate your help to solve my problem since I don't know
where to get more info.

Thanks

---

From: David Charlap <[email-masked]>
Date: Wed, 04 Apr 2001 11:44:29 -0400

Roberto Guglielmi wrote:
>          message , with the checksum field replaced by zero..."
> 

It's the same algorithm used to generate IP header and TCP checksums.

RFC 1071 explains the algorithm, along with detailed explanations, and
sample code in C and some assembly languages.

-- David