We've been trying to get a handle on whether or not the packets on our
hipersocket interfaces are getting broken into smaller than specified MTU for
the interface indicates. Tracepath on SLES9 gives us VASTLY different results
on SLES9 than SLES8. The SLES8 results are what we expect. Tracepath on
SLES9 indicates my MTU is being negotiated DOWNWARDS to 1492 within my own box
before it hits the target. Anoyone got any idea what to make of the
following:
On SLES8:
nokomis:~ # ifconfig hsi1
hsi1 Link encap:Ethernet HWaddr 00:00:00:00:00:00
inet addr:192.168.252.16 Mask:255.255.255.0
inet6 addr: fe80::200:ff:fe00:0/64 Scope:Link
UP RUNNING NOARP MULTICAST MTU:8192 Metric:1
RX packets:2 errors:0 dropped:0 overruns:0 frame:0
TX packets:5 errors:2 dropped:2 overruns:0 carrier:0
collisions:0 txqueuelen:100
RX bytes:632 (632.0 b) TX bytes:16712 (16.3 Kb)
tracepath to z/OS hipersocket at 162.168.252.1
nokomis:~ # tracepath 192.168.252.1
1?: [LOCALHOST] pmtu 8192
1: 192.168.252.1 (192.168.252.1) 0.811ms reached
Resume: pmtu 8192 hops 1 back 1
Tracepath to a SLES9 Linux
On SLES9
nokomis:~ # tracepath 192.168.252.22
1?: [LOCALHOST] pmtu 8192
1: 192.168.252.22 (192.168.252.22) 3.942ms reached
Resume: pmtu 8192 hops 1 back 1
>From that SLES9 system:
hsi0 Link encap:Ethernet HWaddr 00:00:00:00:00:00
inet addr:192.168.252.22 Mask:255.255.255.0
inet6 addr: fe80::200:ff:fe00:0/64 Scope:Link
UP RUNNING NOARP MULTICAST MTU:8192 Metric:1
RX packets:19650 errors:0 dropped:0 overruns:0 frame:0
TX packets:22917 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:18569931 (17.7 Mb) TX bytes:9427612 (8.9 Mb)
abinodji:~ # tracepath 192.168.252.1
1: abinodji.co.hennepin.mn.us (192.168.252.22) 27.575ms pmtu 8192
1: abinodji.co.hennepin.mn.us (192.168.252.22) 0.085ms pmtu 8166
1: abinodji.co.hennepin.mn.us (192.168.252.22) 0.040ms pmtu 4352
1: abinodji.co.hennepin.mn.us (192.168.252.22) 0.048ms pmtu 2002
1: abinodji.co.hennepin.mn.us (192.168.252.22) 0.035ms pmtu 1492
1: 192.168.252.1 (192.168.252.1) 0.932ms reached
Resume: pmtu 1492 hops 1 back 1
To the SLES8 system:
abinodji:~ # tracepath 192.168.252.16
1: abinodji.co.hennepin.mn.us (192.168.252.22) 0.355ms pmtu 8192
1: abinodji.co.hennepin.mn.us (192.168.252.22) 0.057ms pmtu 8166
1: abinodji.co.hennepin.mn.us (192.168.252.22) 0.042ms pmtu 4352
1: abinodji.co.hennepin.mn.us (192.168.252.22) 0.049ms pmtu 2002
1: abinodji.co.hennepin.mn.us (192.168.252.22) 0.034ms pmtu 1492
1: 192.168.252.16 (192.168.252.16) 0.400ms reached
Resume: pmtu 1492 hops 1 back 1
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