low upload speed for SCP/SFTP even PUT to TCP 22 when MPLS IP configured

[Cheng Xing]

Hey guys, we are experiencing the low speed for SCP/SFTP even PUT when we upload file to the server in our network.

And this issue only happens if the server TCP port set as 22. We are an ISP network and do not set up any limit for TCP port. 

The issue only happens when UPLOAD action happens. For example, if from the server using GET or Download a file, there is no issue(the same direction).

The topology like this below

Client - ASR920 - ASR9001 - Internet(server)

All network running MPLS LDP

After multiple tests, if we remove the "mpls ip" under the interface in ASR920 faces ASR9001, the issue gone.

The issue both happens in IOS-XE 3.16/3.18/16.9.4. 

Anyone have any idea about that?

Cheers

Charles

[LloydG]

Hi, did you end up finding out what the problem here was?

[Cheng Xing]

Yes - I logged the ticket to Cisco and finally solved. Please see the solution below.
1. The above symptoms matches the bug "CSCvu90681 Bad throughput on TCP port 22 and 23". It states that for all iOS 16.9.x version, the copp-mpls is enabled by default. This causes the TCP acknowledgements to get punted causing retransmissions and compromised speed.
2. So the work around is to perform the below steps:
* platform qos-feature copp-mpls disable --- disable the copp-mpls
* no platform qos-feature copp-mpls disable --- remove the command
* platform qos-feature copp-mpls disable --- disable it again.
3. The ultimate fix of the bug is to upgrade to 16.12.x version.

[LloydG]

Hi Cheng

Thanks for being helpful on this, perfect answer