Subject: Re: OSPF checksum error between two differents contructors routers

From: Alex Zinin <[email-masked]>
Date: Wed, 12 Jun 2002 18:32:27 -0700

Arnaud,

  What might be happening is one router may be configured
  with MD5 authentication and is expecting the checksum
  to be 0, while another router is using another authentication
  mechanism or none at all. Normally, one would expect the first
  router to complain about the authentication type, but I could
  easily imagine an implementation mistakenly performing these
  checks in a different order.

--
Alex

Friday, May 31, 2002, 3:45:25 AM, you wrote:
> Hi,

> i have got a problem with a multi-constructor network :

> Here is my question : Two equipments are connected in OSPF, one send LSA
> update with a 0xFFFF checksum the second router drop the packet and
> said "checksum eror, should be zero".

> RFC 2328 says : "a checksum should never be zero".

> RFC 905 about Fletcher Checksum says :" one's  complement  arithmetic  in
> which  if  any  of  the variables  has the value minus zero (i.e. 255 "or
> OxFFFF) it shall be regarded as though it was plus zero (i.e. 0).

> Can we conclude wich equipement is wrong : the one which sent the FFFF
> checksum or the one which said should be zero ?

> What i understand is that sending an FFFF checksum is like sending a 0
> cehcksum and it is an wrong value.

> Thanx for helping,