Re: UDP error handling
From: Barry Margolin (barmar_at_alum.mit.edu)
Date: Mon, 04 Apr 2005 15:42:36 -0400
In article <email@example.com>,
"David Schwartz" <firstname.lastname@example.org> wrote:
> "Barry Margolin" <email@example.com> wrote in message
> >> Who said he wasn't using port 53?
> > No one. But that would be ridiculous, so I'll give him the benefit of
> > the doubt.
> Actually, that's not ridiculous. A lot of of firewalls block unknown UDP
> so sometimes people look for ports that the firewalls pass and use them.
> >> And there are many documented cases of
> >> proxies munging data they thought that they understood.
> > URLs, please?
> Are you saying you have never heard of a case where a NAT box 'repaired'
> the checksum of a UDP packet that was received corrupt because it didn't
> check the checksum before rewriting the destination address?
No, I've never heard of a proxy modifying the payload when it doesn't
know the application protocol.
> It's hard to find URLs on the Internet because it's not clear what terms
> to search for. But I have personally dealt with many cases where proxies,
> firewalls, and LSPs thought they understood the data I was sending and made
> manipulations that might be sensible for other protocols but made no sense
> for an arbitrary protocol layered over TCP or UDP.
None of these seem to be examples of what you're describing. I have no
trouble believing the case where a NAT box doesn't verify the checksum
of a received packet before doing the header rewrite.
-- Barry Margolin, firstname.lastname@example.org Arlington, MA *** PLEASE post questions in newsgroups, not directly to me ***