Subject: Re: Path MTU discovery
To: None <tech-net@NetBSD.ORG>
From: Michael Richardson <>
List: tech-net
Date: 07/16/1997 02:56:32

>>>>> "Jonathan" == Jonathan Stone <jonathan@DSG.Stanford.EDU> writes:
    Wolfgang> route add -mtu 4096 -net x.x.x.0 myinterface

    >> Yes, but that isn't the point of PMTU discovery.
    >> The point is to figure out that there are FDDI networks from
    >> A<->B and so that *NON-LOCAL* packets can be bigger.  In any
    >> case, the reason I wanted PMTU code (which I understand now
    >> that FreeBSD has) is because I want to determine if my
    >> implementation of PMTU ICMP's in an IPsec security gateway
    >> works correctly.

    Jonathan> PMTU is also useful if you have an Ethernet subnet at
    Jonathan> home, with a SLIP or PPP connection configured to a low
    Jonathan> MTU (256 bytes) for latency reasons.

  I, for one do. However, since prior to PMTU, you were supposed to
assume an MTU of 576 for non-local TCP connections, it doesn't affect
me. It affects people that have their PPP MTU set to a higher value.
  And, so, if *YOU* access my machine, across my rather loss link, (my
fault, not my ISP's) then doing too much fragmentation affects your
speed. Believe me: I'm across the world, and I know how bad my link

] It isn't that sun never sets; rather dawn and dusk are united | one quark   [
]   Michael Richardson, Sandelman Software Works, Ottawa, ON    | two quark   [
] | red q blue q[
] panic("Just another NetBSD/notebook using, kernel hacking, security guy");  [

Version: 2.6.3ia
Charset: latin1
Comment: Processed by Mailcrypt 3.4, an Emacs/PGP interface