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SubjectNetworking strangeness 2.4.0-ac9 and earlier
Hi all,

I've seen this for a while... the output from netstat and ifconfig do
not agree on the MTU of the device:

[root@lion /root]# netstat -r
Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt
Iface
10.1.11.0 * 255.255.255.0 U 40 0 0
eth0
127.0.0.0 * 255.0.0.0 U 40 0 0
lo
default spqr 0.0.0.0 UG 40 0 0
eth0

[root@lion /root]# ifconfig
eth0 Link encap:Ethernet HWaddr 00:10:4B:2B:12:80
inet addr:10.1.11.76 Bcast:10.1.11.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:3648 errors:77 dropped:0 overruns:0 frame:144
TX packets:3863 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
Interrupt:11 Base address:0xd800

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16192 Metric:1
RX packets:139 errors:0 dropped:0 overruns:0 frame:0
TX packets:139 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0

AFAIK, the MSS value should be about 40 less than the MTU, not 40,
though on other Linux boxes I have, the MSS column from netstat shows 0
(both of them are 2.2 kernels and single proc machines). This machine is
a dual P3-500 with 512mb of RAM and a 3COM 3c905 card. I understand that
the MSS column should actually read the MTU, but I don't know if that is
the case. Either way cat /proc/net/route shows:

Iface Destination Gateway Flags RefCnt Use Metric
Mask MTU Window
IRTT
eth0 000B010A 00000000 0001 0 0 0
00FFFFFF 40 0
0
lo 0000007F 00000000 0001 0 0 0
000000FF 40 0
0
eth0 00000000 FE0B010A 0003 0 0 0
00000000 40 0 0

One of the things that seem to be symptomatic of the problem is web
browsing to my Ultra 5 (Solaris 2.6 with recommended patches). A single
web page can take several minutes to load with all images on my local
LAN, but on the other Linux machines, it blows in before you can blink
(as would be expected). Similar behaviour can be seen browsing against
other Linux machines as well, though not as bad. Other network protocols
are slower as well (FTP, telnet), though not once it gets through the
firewall, oddly enough.

Any help appreciated.

Thanks,
John
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