Re: UDP bugs

Richard Gooch (rgooch@atnf.csiro.au)
Mon, 14 Dec 1998 12:53:33 +1100

kuznet@ms2.inr.ac.ru writes:
> Hello!
>
> > Right (silly me!), but what about the input size limits Richard mentioned?
> > Is it possible that the reassembler has bugs in this regard?
>
> rmem_max == 65535 by default.
>
> Taking into account 16 bytes of mac header and 4+alignment
> for skb refcnt socket with default rmem_max can receive
> only 65476 byte frames.
>
> So that, to play with such frames or with IPv6 jumbograms
> rcvbuf must be increased. By user/admin, rather than by default,
> certainly.

Yes, I've just tried:
int buflen = 65536 + 32;
setsockopt (fd, SOL_SOCKET, SO_RCVBUF, &buflen, sizeof buflen);

and now I can send and receive packets with payload size of 65507
bytes with Linux 2.1.126+.

Now, with Linux 2.1.126 -> Linux 2.0.36, I was limited to 51792 bytes
payload. By increasing the SO_RCVBUF I can take that up to 52840
bytes, approximately. This is harder to determine because I'm going
from a switch to a hub and hence competing for bandwidth, so I'm
getting some packet loss.

Regards,

Richard....

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