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тАО03-29-2011 05:06 AM
тАО03-29-2011 05:06 AM
I've a machine:
Model: "ia64 hp server Integrity Virtual Machine"
Release: HP-UX B.11.31
Machine: ia64
and I've an issue with my lan.
#netstat -ivwn
Name Mtu Network Address Ipkts Ierrs Opkts Oerrs Coll
...
lan2 9000 172.21.3.0 172.21.3.2 60752 0 61920 0 0
lan1 1500 192.168.172.0 192.168.172.120 14431 0 14335 0 0
lan0 1500 192.168.171.0 192.168.171.141 75 0 361 0 0
1) lan2 has MTU=9000
#traceroute -s 172.21.3.2 -r -F 172.21.3.1 9000
traceroute to 172.21.3.1 (172.21.3.1) from 172.21.3.2, 30 hops max, 9000 byte packets
1 * * *
2) lan1 has MTU=1500
#traceroute -s 192.168.172.120 -r -F 192.168.172.119 9000
traceroute to 192.168.172.119 (192.168.172.119) from 192.168.172.120, 30 hops max, 9000 byte packets
1 192.168.172.120 (192.168.172.120) 0.117 ms !F 0.055 ms !F 0.034 ms !F
3) lan0 has MTU=1500
#traceroute -s 192.168.171.141 -r -F 192.168.171.140 9000
traceroute to 192.168.171.140 (192.168.171.140) from 192.168.171.141, 30 hops max, 9000 byte packets
1 192.168.171.141 (192.168.171.141) 0.977 ms !F 0.057 ms !F 0.044 ms !F
Why lan2 behaves in a different way ?
How can I detect the problem ?
I don't know if the different behave depends on OS settings or on network/switches settings.
Thanks in advance.
Best Regards.
Raffaele
Solved! Go to Solution.
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тАО03-29-2011 05:56 AM
тАО03-29-2011 05:56 AM
Re: TCP Segment size
UNIX because I majored in cryptology...
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тАО03-29-2011 06:51 AM
тАО03-29-2011 06:51 AM
Re: TCP Segment size
thanks for your reply.
I had the same problem too when lan2 had MTU=1500. According to you, I think the problem depends on switch configuration, but I'm not sure.
Thanks again.
Regards
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тАО03-29-2011 07:03 AM
тАО03-29-2011 07:03 AM
Re: TCP Segment size
if regardless of the frame size, you always had a problem with this interface, it is always a good idea to check the other end of the network cable, i.e., the switch port. It might be dead, it might be assigned to a wrong VLAN, it might be configured to use trunking, which I am assuming you are not using. One of many reason may cause this disconnect and if you are controlling only one side, the server side, of the problem, you can not make decisive conclusions where the problem resides.
UNIX because I majored in cryptology...
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тАО03-29-2011 07:16 AM
тАО03-29-2011 07:16 AM
Re: TCP Segment size
i.e.
If I set MTU=1500
I can transmit a packet size less than 1497
(traceroute -s source -r -F target 1496 )
If I set MTU=9000
I can transmit a packet size less than 8997
#traceroute -s 172.21.3.2 -r -F 172.21.3.1 9000
traceroute to 172.21.3.1 (172.21.3.1) from 172.21.3.2, 30 hops max, 9000 byte packets
1 * * *
#traceroute -s 172.21.3.2 -r -F 172.21.3.1 8996
traceroute to 172.21.3.1 (172.21.3.1) from 172.21.3.2, 30 hops max, 8996 byte packets
1 * cosbedb1-priv (172.21.3.1) 0.726 ms 0.507 ms
while with other interface I can transmit a packet size greater than MTU. I would know if I can set OS parameters to get the same behaviour.
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тАО03-29-2011 08:55 AM
тАО03-29-2011 08:55 AM
Re: TCP Segment size
Configuration parameters for this are ndd related and Rick Jones of these forums is the expert on ndd configuration. I see from his profile that he is still active and posting. So, when he sees this post, I am sure he can tell you how you can change the things (or why you should not).
UNIX because I majored in cryptology...
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тАО03-30-2011 08:43 AM
тАО03-30-2011 08:43 AM
Re: TCP Segment size
As for why the 9000 byte traceroute worked, that isn't a "problem" it is just IP doing what it is supposed to do. When handed a datagram larger than the next-hop MTU, IP will fragment it into fragments that fit in the next-hop MTU and transmit them. When the arrive at the destination, the destinations IP stack will reassemble the fragments into complete datagrams and pass them up the stack.
Also, thusfar, none of this has been the TCP Segment size.
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тАО03-31-2011 01:11 AM
тАО03-31-2011 01:11 AM
Re: TCP Segment size
thanks for your reply and sorry for the wrong subject.
"When handed a datagram larger than the next-hop MTU, IP will fragment it into fragments that fit in the next-hop MTU and transmit them. When the arrive at the destination, the destinations IP stack will reassemble the fragments into complete datagrams and pass them up the stack."
Why it appens only in lan0 and lan1 ?
Why only in lan2 I can't transmit a datagram larger than MTU ?
Thanks again,
Regards.
Raffaele
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тАО03-31-2011 01:21 AM
тАО03-31-2011 01:21 AM
Re: TCP Segment size
does lan2 work with smaller datagram sizes like e.g. 1500? What if you set the MTU size to 1500 for lan2? To debug this, you should try the following cases for lan2:
- datagram size 1500, MTU 9000
- datagram size 9000, MTU 9000 -> checked, seems not to work
- datagram size 1500, MTU 1500
- datagram size 9000, MTU 1500
Like Mel wrote it, for jumbo frames to work you need to set it on both sides. Maybe it's a problem on the switch side.
Unix operates with beer.
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тАО03-31-2011 01:55 AM
тАО03-31-2011 01:55 AM
Re: TCP Segment size
does lan2 work with smaller datagram sizes like e.g. 1500?
Yes, it works.
What if you set the MTU size to 1500 for lan2?
I can transmit datagram less than 1497.
To debug this, you should try the following cases for lan2:
- datagram size 1500, MTU 9000 -> OK
- datagram size 9000, MTU 9000 -> KO !
- datagram size 1500, MTU 1500 -> KO !
- datagram size 9000, MTU 1500 -> KO !
Thanks a lot for your help.
Regards,
Raffaele