MTU issue over LAN

[thiyagarajankalaiselvan]

Hi All,

I'm working on intermittent application access over LAN. From the longs can anybody help me to know how to fix this mtu mis-match issue.

Below  is the logs I have collected from the switch:

May  2 10:09:51.123 UTC: TCB037284C0 created

May  2 10:09:51.123 UTC: TCB037284C0 setting property TCP_VRFTABLEID (14) 372D53E

May  2 10:09:51.123 UTC: TCB037284C0 setting property TCP_TOS (1) 372D498

May  2 10:09:51.123 UTC: TCB037284C0 bound to 10.59.100.1.14337

May  2 10:09:51.123 UTC: TCP: sending SYN, seq 2841499684, ack 0

May  2 10:09:51.123 UTC: TCP1: Connection to 10.99.93.27:80, advertising MSS 536

May  2 10:09:51.123 UTC: TCP1: state was CLOSED -> SYNSENT [14337 -> 10.99.93.27(80)]

May  2 10:09:51.157 UTC: TCP1: state was SYNSENT -> ESTAB [14337 -> 10.99.93.27(80)]

May  2 10:09:51.157 UTC: TCP1: Connection to 10.99.93.27:80, received MSS 1440, MSS is 536

May  2 10:09:51.157 UTC: TCB037284C0 connected to 10.99.93.27.80

May  2 10:09:55.419 UTC: TCP1: bad seg from 10.99.93.27 -- bad sequence number: port 14337 seq 1078448220 ack 2841499685 rcvnxt 1078448221 rcvwnd 4128 len 0

May  2 10:10:01.417 UTC: TCP1: bad seg from 10.99.93.27 -- bad sequence number: port 14337 seq 1078448220 ack 2841499685 rcvnxt 1078448221 rcvwnd 4128 len 0

May  2 10:10:13.413 UTC: TCP1: bad seg from 10.99.93.27 -- bad sequence number: port 14337 seq 1078448220 ack 2841499685 rcvnxt 1078448221 rcvwnd 4128 len 0

May  2 10:10:31.021 UTC: TCP0: state was TIMEWAIT -> CLOSED [13467 -> 10.99.95.90(49)]

May  2 10:10:31.021 UTC: TCB 0x3729918 destroyed

May  2 10:10:37.614 UTC: TCP1: bad seg from 10.99.93.27 -- bad sequence number: port 14337 seq 1078448220 ack 2841499685 rcvnxt 1078448221 rcvwnd 4128 len 0

Regards,

Thiyagu

[Reza Sharifi]

What is the issue?

Can you post config?

[thiyagarajankalaiselvan]

Hi Reza,

The issue is intermittently users were unable access Internet/Intranet applications.

Do you need the switch configuration?

Regards,

Thiyagu

[Reza Sharifi]

Hi,

Provide more info and tell us how everything is connected together. Is the device you are having issue with connected to a switch? If yes, what type of switch. If the issue is the switch post "sh run" and tell us what port you have issue with.  Is there a router in your design?

Overall, provide more details.

HTH

[Joseph W. Doherty]

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting

I suspect there's more of an issue than MTU with the information you've posted.  It's very difficult to solve underling issue given just what you've posted.

However, as to the MSS differences of 536 and 1440, and since you believe you have a MTU issue, 536 often indicates PMTUD isn't enabled on one host and the two hosts are not on the same subnet.

[thiyagarajankalaiselvan]

Hi All,

Can anybody help me to know how to enable path MTU on cisco WS-C3750-48P?

I have tried changing the MTU value on VLAN and the host connected switch port but I could not set the MTU value.

Thanks a lot in adavance.

Regards,

Thiyagu.

[Joseph W. Doherty]

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

If you mean to the 3750 itself, try:

ip tcp path-mtu-discovery