Unable to transfer file across MPLS Network

[bktkruppw]

We recently have come across not being able to transfer files across our MPLS link one way only.  We have disabled WAAS, QoS Policy and have rebooted our Core Switches(6506 and Nexus 7009) with no luck.  We can transfer files to the remote site, but they cannot transfer various files back to us. We failed over to our backup lines and can transfer the files across with no problems.  When we run a capture, we are seeing duplicate ACK's.

Any thoughts to what can cause this?

[Joseph W. Doherty]

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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.

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Posting

Dup ACKs might be due to lost packets or out-of-sequence packets.  Sometimes if there's enough packet loss, higher level will give up data transfer.

Are you unable to transfer any size file, even tiny, or just bigger files?

[bktkruppw]

It's various file types and sizes than will not transfer.

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[thomas.g.fan]

is there a firewall in the path? you can trace route on machine a in site a to machine b in site b and also on machine b in site b to machine a in site a then have a look if they are taking the same path.

[bktkruppw]

One way has 7 hops the other way has 8 hops.

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[Harold Ritter]

Hi,

This sounds like it could be MTU related. Did you check the path MTU of the primary path vs the back up path?

Regards

[bktkruppw]

How? We have local routers that peer with AT&T.

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[Harold Ritter]

Hi,

Try pinging from the file transfer client to the server with 1500 bytes and setting the do not fragment bit in the echo request.

windows:

ping -f -l 1500

mac:

ping -D -s 1500

Regards

[bktkruppw]

Says Pavket needs to be fragmented but DF set.

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[Harold Ritter]

Hi,

That definitely sound like a MTU issue then.

I would try a few other things.

1. Try the same test with the secondary path.

2. Try reducing the packet size on the primary path until the packet gets through to determine what is the path mtu.

3. Try the ping -f -l 1500 on the primary path with the sniffer enabled so you can find out which router send you the ICMP "Fragmentation Needed and Don't         Fragment was Set" message.

Regards

[bktkruppw]

Ran the ping down from 1500 and it goes through at 1472 on the server.

[Harold Ritter]

It certainly looks like this would be the issue.

How about 1. and 3.?

Regards

[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 should have 1500 MTU across your MPLS, take this up with your SP.

If you need to use the link now, if any of your equipment supports it, using ip mss-adjust tcp, set 40 bytes less then the max MTU may allow your file transfers to work.

PS:

Unless something is really broken, which it may be as why you're seeing fragmentation at all, fragmentation working correctly should allow your files to transfer.

[LukaszTJB]

The mtu is here 1500 bytes. You have to calculate 8 bytes for the UDP Header and 20 bytes for the ip Header while defining the datagram size.


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[Harold Ritter]

Hi Lukasz,

You are correct. I had forgotten that the size specified by the -l is just the payload, as I do extended from routers most of the time.

Thanks