[sclug] Bizarre IMAP problem

[Alex Butcher]

On Thu, 25 Aug 2005, Roland Turner (SCLUG) wrote:

> Alex Butcher wrote:
>
>
>> Even better, ifconfig eth0 mtu 576, which is the largest MTU that is
>> guaranteed to traverse any and all types of network without fragmentation.
>
>
> Interesting; where does this number come from? (A spec somewhere, or
> simply the observed behaviour of lots of different IP carriers?) This[1]
> MS KB article states:
>
>
>    The Internet standard for MTU is 576.
>
>
> without attribution. The google search "site:ietf.org mtu 576" yields _no_
> hits which suggests that, if it is a standard, it's certainly not a formal
> one.

It is as formal as any other Internet standard:

"All hosts must be prepared to accept datagrams of up to 576 octets (whether
  they arrive whole or in fragments).  It is recommended that hosts only
  send datagrams larger than 576 octets if they have assurance that the
  destination is prepared to accept the larger datagrams."
  - RFC791, Internet Protocol

It's worth skimming the RFCs referenced in section 3.2 of STD1 sometime (at
least upto 959 or so, anyway, unless you're doing routing, funny
transport-layer protocols, or SNMP).

> - Raz

Best Regards,
Alex.
-- 
Alex Butcher      Brainbench MVP for Internet Security: www.brainbench.com
Bristol, UK                      Need reliable and secure network systems?
PGP/GnuPG ID:0x271fd950                         <http://www.assursys.com/>