TCP/UDP checksum error with IP masquerading

TCP/UDP checksum error with IP masquerading

Post by Laze » Tue, 09 Dec 1997 04:00:00

I'm running IP masqurading on my linuxbox with a modem connected to
internet and Win95 computers on the LAN network. After a while I get
alot of checksum errors in /var/log/messages like:
Kernel: MASQ failed TCP/UPD checksum from x.x.x.x!
where x.x.x.x is some IP on the internet.

I'm using ipfwadm:
ipfwadm -F -p accept
ipfwadm -I -p accept
ipfwadm -O -p accept
ipfwadm -a masquerade -S -D

What causes the checksum errors???


1. IP masquerading : TCP/UDP checksum errors

Firewall consisting of 2 linux boxes,
linux box with ISDN modem has (now) slackware 2.0.30 (with todays pre-31-2
patch), used to be 2.0.30, 2.0.29, 2.0.27.

using diald/ppp to connect to provider.

Things work fine and shiny, most of the time,
only every now and then we get the horrendous TCP/UDP checksum error,
resulting in stalled netscape

(just half an hour ago netscape hung itself after almost having dopwnlaoed
the 4.01 version ;( ...)

I checked the IP_masq webpages, and they suggest *not* using an MTU lower
than 1500 ??

Could anyone shed some light on this ??

Thanks muchos

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