nanog mailing list archives
Re: Broken PMTU (was: Who does source address validation? (was Re:what's that smell?))
From: Tony Rall <trall () almaden ibm com>
Date: Thu, 10 Oct 2002 15:07:01 -0700
On Thursday, 2002-10-10 at 00:55 ZE2, Iljitsch van Beijnum <iljitsch () muada com> wrote:
You can also get around this by making the first hop the one with the lowest MTU. This is no fun for ethernet-connected stuff, but for dial-up this is easy. Then this box will announce a smaller TCP MSS when the connection is established and there aren't any problems.
Traffic consists of more than tcp; setting your mtu low might get your tcp traffic delivered but won't help inbound traffic using other protocols. Mtu discrepancies must be dealt with in at least one of the following ways if you don't want it to lead to fatally dropped packets: 1. Fragmentation must work. This applies to systems that don't use PMTUD or use blackhole detection. (Some folks think it a good "security" practice to drop fragments! Some nat boxes don't know what to do with fragments when they arrive out of order - especially a non-initial fragment before the first.) 2. PMTUD must work. 3. PMTUD blackhole detection must be used with operable fragmentation. (If you have to fallback to this you're likely to suffer significant performance hits.) Tony Rall
Current thread:
- Re: Who does source address validation? (was Re: what's that smell?), (continued)
- Re: Who does source address validation? (was Re: what's that smell?) David Schwartz (Oct 09)
- Re: Who does source address validation? (was Re: what's that smell?) Stephen Stuart (Oct 09)
- Re: Who does source address validation? (was Re: what's that smell?) alex (Oct 09)
- Re: Who does source address validation? (was Re: what's that smell?) David Schwartz (Oct 09)
- Re: Who does source address validation? (was Re: what's that smell?) alex (Oct 09)
- Re: Who does source address validation? (was Re: what's that smell?) Sean Donelan (Oct 09)
- Re: Who does source address validation? (was Re: what's that smell?) Stephen J. Wilcox (Oct 09)
- Re: Broken PMTU (was: Who does source address validation? (was Re:what's that smell?)) Iljitsch van Beijnum (Oct 09)
- Re: Broken PMTU (was: Who does source address validation? (was Re:what's that smell?)) Valdis . Kletnieks (Oct 09)
- Re: Broken PMTU (was: Who does source address validation? (was Re:what's that smell?)) Stephen J. Wilcox (Oct 10)
- Re: Broken PMTU (was: Who does source address validation? (was Re:what's that smell?)) Tony Rall (Oct 10)
- Re: Who does source address validation? (was Re: what's that smell?) Valdis . Kletnieks (Oct 09)
- Re: Who does source address validation? (was Re: what's that smel l?) Steve Francis (Oct 09)
- Re: Who does source address validation? (was Re: what's that smel l?) Valdis . Kletnieks (Oct 09)
- Re: Who does source address validation? (was Re: what's that smel l?) Hank Nussbacher (Oct 10)
- Re: Who does source address validation? (was Re: what's that smell?) Richard A Steenbergen (Oct 10)
- Re: Who does source address validation? (was Re: what's that smell?) Iljitsch van Beijnum (Oct 10)
- Re: Who does source address validation? (was Re: what's that smell?) Jared Mauch (Oct 10)
- Re: Who does source address validation? (was Re: what's that smell?) Iljitsch van Beijnum (Oct 12)