Drops on Tunnel interface

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Sep 4th, 2009
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I am getting drops on tunnel interface on the router. Tunnel interface and configurations are attached with this email. This is a 5 Mbps link on fiber and the traffic is going not above 2.5 Mbps but still I am getting drops. There are no drops on the physical interface whereas drops are seen on the tunnel interface.



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u1kumar2002 Fri, 09/04/2009 - 23:01
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Hi Saad,

If you are facing drops in tunnel interface Plz check the usage. If the usage is more than physical link bandwidth. This could be one reason.

I don't know how to open the attachment i this forum. Can u plz share that how i can see u attachment. So that i can get better understanding. I am new in this forum.I tried but i am not able to see the attachment

waridtel.com Sat, 09/05/2009 - 01:03
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The physical interface is FE i.e. 100 Mbps while the traffic is around 2.5 Mbps.

You can open the attachment by clicking the arrow key pointing downwards.


waridtel.com Sat, 09/05/2009 - 03:24
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Please help me out with this. I am facing severe issues because of this problem.


Mohamed Sobair Sat, 09/05/2009 - 04:32
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This could be due to IP Fragmentation issue.

I would set it as follows:

1- remove the (IP MTU 1400) command from the tunnel interface.

2- configure (Tunnel path MTU discovery) command on both tunnel interfaces.

3- On the Physical interface try to drop the IP MTU to 1476 as the GRE tunnel would add 20 Byte for the IP header and 4 Byte GRE header.

let us know the result,


waridtel.com Sat, 09/05/2009 - 04:54
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Thanks for your reply.

As per your suggestion I should:

1) remove ip mtu 1400 command from tunnel interface

2) configure "tunnel path mtu discovery" on the tunnel interfaces.

3)On the physical interface I should write the command "ip mtu 1476"

Please confirm me. Thanks.


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