We've been seeing some disturbing differences between the packet size being
(aparrently) sent on SLES9 vs SLES8 over the hipersocket interface.
The tool we have been using to tell us the packet length going over the
hipersocket is tracepath.
On SLES8:
nokomis:~ # uname -r
2.4.21-83-default
nokomis:~ # tracepath 192.168.252.1
1?: [LOCALHOST] pmtu 57344
1: 192.168.252.1 (192.168.252.1) 2.133ms reached
Resume: pmtu 57344 hops 1 back 1
nokomis:~ #
on SLES9:
abinodji:~ # tracepath 192.168.252.1
1: abinodji.co.hennepin.mn.us (192.168.252.22) 0.267ms pmtu 57344
1: abinodji.co.hennepin.mn.us (192.168.252.22) 0.129ms pmtu 32000
1: abinodji.co.hennepin.mn.us (192.168.252.22) 0.107ms pmtu 17914
1: abinodji.co.hennepin.mn.us (192.168.252.22) 0.055ms pmtu 8166
1: abinodji.co.hennepin.mn.us (192.168.252.22) 0.046ms pmtu 4352
1: abinodji.co.hennepin.mn.us (192.168.252.22) 0.047ms pmtu 2002
1: abinodji.co.hennepin.mn.us (192.168.252.22) 0.035ms pmtu 1492
1: hawk.hipersocket (192.168.252.1) 0.834ms reached
Resume: pmtu 1492 hops 1 back 1
At first we thought it was a problem with tracepath between the releases.
So I took the executeable for tracepath on SLES-8 and copied to to SLES-9 -
Wasn't even sure it would run... But it did and revealed different
behaviour, identical to that of the SLES9 Tracepath:
abinodji:~ # ./tracepath_sles8 192.168.252.1
1: abinodji.co.hennepin.mn.us (192.168.252.22) 0.258ms pmtu 57344
1: abinodji.co.hennepin.mn.us (192.168.252.22) 0.127ms pmtu 32000
1: abinodji.co.hennepin.mn.us (192.168.252.22) 0.157ms pmtu 17914
1: abinodji.co.hennepin.mn.us (192.168.252.22) 0.057ms pmtu 8166
1: abinodji.co.hennepin.mn.us (192.168.252.22) 0.045ms pmtu 4352
1: abinodji.co.hennepin.mn.us (192.168.252.22) 0.046ms pmtu 2002
1: abinodji.co.hennepin.mn.us (192.168.252.22) 0.037ms pmtu 1492
1: hawk.hipersocket (192.168.252.1) 0.342ms reached
Resume: pmtu 1492 hops 1 back 1
So there is some fundamental difference between SLES-8 and SLES-9 and from what
I can see no matter WHAT my hipersocket MTU size is (in this case
57344) I appear to be getting packet sizes of 1492 on SLES9.
Note that the PMTU discovery is hitting the SAME interface/.IP address 7 times
before it completed to the target. 192.168.252.22 is HSI Ip address of
Abinodji, and 192.168.252.1 is the address of the target z/OS LPAR image on
which we run DB2/Shadow direct.
Anyone have any idea as to whether or not I am actually having my packets
shredded to 1492, and if so Why?
The CHPID, the Linuxes and the z/OS target all have the correct settings for an
MTU of that size (chpid 64K, the MTU for interfaces 64K less 8K
overhead).
I've had this open with Novell for about three weeks and they're of absolutely
NO help.
Thanks,
-J
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