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Community Member

Problem With MTU...

Hi all..

I have one setup ....Mumbai-----Delhi with MPLS Ethernet link at both end.

My connectivity is working fine..I am able to ping Mumbai to delhi.But problem is that when i ping from Delhi to Mumbai Lotus server with load 1473....

ping 10.2.15.1 -l 1473 It getting Request Time Out.

When I ping the same IP address with load 1472 and below it work fine.

Config at Both end Router same like....

interface FastEthernet0/1
description ******
ip address 172.22.2.29 255.255.255.252
ip route-cache flow
duplex auto
speed auto

Note: When i ping from Mumbai lotus server with load 1473 to delhi client pc..It works.

I tried follwing command, but this is maximum value.....can we configure above this value on router interface...

ip tcp adjust-mss 1460

Is it MTU problem or any?

Thanx.......Any help will appriciated in any manner......

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Re: Problem With MTU...

Hello,

"DF" bit indicates to the network that the packet should not be fragmented. This becomes an issue if somewhere down the path, one of the devices cannot handle the packet in its entirety and needs it to be fragmented. The "DF" bit is generally set by the source device application. In case of ping, you have to manually set it using "-f" flag. If you have not done so, that means some device down the path is not able to handle 1473 bytes and is not able to fragment as well (your host will have its MTU set at 1500, so it will not fragment the packet).

Regards,

NT

4 REPLIES
Cisco Employee

Re: Problem With MTU...

Hello,

It does look like an MTU issue. Are you setting the DF bit? Also, do you have a firewall before the Lotus Server?

Regards,

NT

Community Member

Re: Problem With MTU...

Hi......

Thanx a lot....for Ur reply....

I don't have a firewall between client and server.

Can you bit explain "DF bit" and where i have to set?

Regards,

Arjun................................

Cisco Employee

Re: Problem With MTU...

Hello,

"DF" bit indicates to the network that the packet should not be fragmented. This becomes an issue if somewhere down the path, one of the devices cannot handle the packet in its entirety and needs it to be fragmented. The "DF" bit is generally set by the source device application. In case of ping, you have to manually set it using "-f" flag. If you have not done so, that means some device down the path is not able to handle 1473 bytes and is not able to fragment as well (your host will have its MTU set at 1500, so it will not fragment the packet).

Regards,

NT

Community Member

Re: Problem With MTU...

Hi...NT

Thanx a Lot.......

That is very good explanation and clear lots of thing..

But how can I overide this problem....regarding that whether i have to speak with service provider (issue if somewhere down the path, one of the devices cannot handle the packet in its entirety and needs it to be fragmented).

Thanx....once again

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