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wrong mtu value in /proc/net/route

DISCUSSION Bruce Cran 3 participants 3 messages Jul 25, 2002 – Jul 26, 2002

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Bruce Cran

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#0 lore raw

I've found something strange going on in 2.4 kernels - when I run
'netstat -r' I get the routing table from /proc/net/route. The MSS
value reported is only 40 bytes, and when I run 'cat
/proc/net/route I'm told that the _MTU_ is 40 bytes. I thought the MSS was
supposed to be the MTU - 40 bytes, not 40 bytes in
total, where the MTU for ethernet is 1500. If I run ifconfig, it reports the
correct MTU of 1500 for eth0 and 16463 for lo. This computer has a NetGear
FA311 card, and is running 2.4.19-pre7-ac2, though I've also seen this happening on a 2.4.18 kernel.

--

Bruce Cran

#1 lore raw
Quoted 9 lines · Bruce Cran

I've found something strange going on in 2.4 kernels - when I run
'netstat -r' I get the routing table from /proc/net/route. The MSS
value reported is only 40 bytes, and when I run 'cat
/proc/net/route I'm told that the _MTU_ is 40 bytes. I thought the MSS
was supposed to be the MTU - 40 bytes, not 40 bytes in
total, where the MTU for ethernet is 1500. If I run ifconfig, it reports
the correct MTU of 1500 for eth0 and 16463 for lo. This computer has a
NetGear FA311 card, and is running 2.4.19-pre7-ac2, though I've also seen this happening on a 2.4.18 kernel.

I see the same values on 2.4.19-rc3-ac3 with two Winbond Electronics Corp W89C940 NIC's. no idea what is causing it.

Rudmer

#2 lore raw
Quoted 5 lines · Rudmer van Dijk
Quoted 4 lines · Bruce Cran

I've found something strange going on in 2.4 kernels - when I run
'netstat -r' I get the routing table from /proc/net/route. The MSS
value reported is only 40 bytes, and when I run 'cat
/proc/net/route I'm told that the _MTU_ is 40 bytes. I thought the MSS

[snip]

Quoted 3 lines

I see the same values on 2.4.19-rc3-ac3 with two Winbond Electronics Corp W89C940 NIC's. no idea what is causing it.

Same here with:

Kernel 2.4.18-pre8
eth0: NE2000 found at 0x240, using IRQ 10.
eth1: 3c5x9 at 0x320, 10baseT port, address 00 60 97 ad 3f 84, IRQ 5.
eth2: RealTek RTL8139 Fast Ethernet at 0xd8855000, 00:50:bf:ea:0f:41, IRQ 9

Kernel 2.4.18
Ethernet controller: 3Com Corporation 3c905C-TX [Fast Etherlink]

Kernel 2.4.19-rc1
eth0: RealTek RTL8139 Fast Ethernet at 0xe0863f00, 00:20:ed:1d:fe:2a, IRQ 5

Again, ifconfig on both machines shows the correct values.

I've not gotten around to trying 2.4.19-rc3 yet.

-Ath

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