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Problems with active FTP over Cisco Routers

Here is my setup.

My company connects to a vendor via MPLS over Cisco 1800 series routers.  We are having problems when we try and do active FTP to our vendors server.  We get packet retransmits.  The packets do not go through a firewall on our side only the router to get out but my vendor does have a firewall on his side.

My understanding is that this type of retransmit can occur if there is a firewall between you and the FTP server that does not have a inspect statement in place.  

What I am trying to do is rule out any issue on our side.  My thoughts are our routers are just forwarding the traffic.  There is no firewall on these routers so I can't see were there would be an active/passive issue until we get to the vendors fiirewall.  Am I missing something?

I have done a packet sniff in active an passive modes and it shows retransmits in active mode but not passive so I know it's not a media problem such as bad cable etc..  My problem is I can't see where this is happening but I suspect at their firewall.

Any help would be GREATLY apprecaited.
1 Solution
There is no firewall on your side, but is there any NAT? If there is no NAT on your side, then as you said, you are simply switching packets and it is very likely on their end.

One other thing to check is for a software firewall on the FTP server machine. But I don't think even that would cause this issue.

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