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SubjectRe: [2.1.94] stoopid ISP/possible tcp bug (kinda long)
On Thu, 9 Apr 1998, Kevin Fenzi wrote:

>
> Hi again.
>
> Once again I am seeing a tcp oddity. This might be unfixable, but I
> thought I would bring it up in case it's exposing a linux tcp bug.
>
> The situation:
>
> My friend gets on the net through a ppp connection to an ISP. He sets
> his mtu to 552 to get better interactive proformance.
> His ISP stupidly deny's all icmp to their modem pool. :(

I was suffering the same problem for a slightly different reason. The
Ascend Max 4k that I connect to was not honoring the MTU I specified and
pppd wasn't forcing the issue either.

I ended up with a (client's perspective) MTU 552 and MRU 1524. This
caused all sorts of havoc: lousy TCP performance and often freezes like
the one you describe above. This took a while to figure out as ifconfig
does not tell you what your MRU is, I had to look at "pppd debug" traces
- you might want to do the same.

Interactive sessions would freeze when full segments of data were being
sent (eg. when I executed a command which output a fair amount of data)
normal typing would not trigger the freeze.

I "solved" it by not specifying a MTU on the client and just using the
Max's default of 1524. At least until Ascend process my trouble ticket
;)

Regards,
Damien Miller

| WWW: http://silicon.vitnet.com.sg
| PGP public key: send me an email with "send file pgp_key" as the subject


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