Re: Name lookup timeouts, redux -- IP defrag?

[Kay Roemer <roemer@informatik.uni-frankfurt.de>]

> 
> As you may recall, I recently reported problems with name lookup
> (gethostname(), nslookup, etc.)  After some experimentation, I've
> discovered that the critical variable is the size of the nameserver
> reply packet -- in particular, its size relative to the MTU of the SLIP
> connection.  For instance, the reply packet from the campus nameserver
> for www.cygnus.com is 286 bytes long.  With an MTU of 256, this lookup
> consistently fails; with an MTU of 350, it consistently succeeds, but
> other lookups with longer reply packets consistenly fail.
> 
> This suggests a bug in IP defragmentation; the nameserver reply packet
> appears to be getting dropped if and only if it gets fragmented.  Has
> anyone else observed a similar problem?  Is anyone else successfully
> running a SLIP connection with an MTU in the neighborhood of 256?

Hmm, I have an MTU of 296 and no problems with the name server at all.
Are you sure you have the same MTU on both sides of the link? If your
local MTU is < than the remote one than the local SLIP will drop all packets
that are longer than local MTU but shorter or equal the remote MTU (ie almost
all IP fragments will be dropped in this case).

Anyway, I'll have a look at it.

Kay.
--
Kay Roemer              roemer@informatik.uni-frankfurt.de
"If I ever meet ..."    http://www.uni-frankfurt.de/~roemer/
"... myself I'll hit myself so hard I won't know who hit me" (Zaphod)