DMVPN and FTP issue

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Oct 25th, 2008
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Using DMVPN phase 3, using one Cisco 3845 as a hub and one Cisco 2851 as Spoke, connected to MPLS cloud CE routers that belong to provider and we have no access to them-

For testing the line, we use the ping and works with no problem with no drops and with latency of 8 ms from the Ottawa Hub to Montreal spoke.

But when we start FTP session with size of the file equal to 16 meg, the FTP paused for at least 4 seconds and we notice that the ping "from Ottawa to Montreal using the same laptop as FTP" latency was going from 80 ms to 145 ms with TTL=126.

To troubleshoot we :

1) Checked the speed and duplex with the provider "CE routers", all are OK "no errors and collisions on their interfaces and the same on our C routers".

2) Connected our laptop directly to CEs in Ottawa and Montreal and did FTP worked with no pause and no lost of the connection where doing the ping and the latency was the same going from 80 ms to 145 ms. We know now that the problem is in our side in the "Hub and Spoke" routers.

3) Remove these commands in the tunnel0 in our Hub and spoke with no success "Still losing connection when doing FTP"

no ip tcp adjust-mss 1360

no ip mtu 1400

I attached the configs of the Hub and spoke.


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Farrukh Haroon Mon, 10/27/2008 - 05:49
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Removing those commands will only 'increase' your problem. Try putting them back and then capture FTP transfer packets. Then you can analyze them in Wireshark etc.

It would be nice if you can capture some packets when the laptop is directly connected as well. This would help you compare things. Most probably is a MTU/MSS kind of issue.



guibarati Mon, 10/27/2008 - 06:04
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Hi, it's not in the file you attached, but, are you using NAT in the HUB?

If so please post the lines with nat config.

I had the same problem. And it was specific with ftp.

guibarati Thu, 10/30/2008 - 18:06
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Have you found a solution to that already?


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