Slow upload speed ASA 5512-x

[thijs.hemmen]

Hi All,

The problem as described in the title of this post is something I'm having for over a year now. The download speed behind the Cisco ASA 5512-x is perfectly fine and stable at 10MBps, but the upload speeds is at most 10% of it. While we are on a 10MBps/10MBps fiber connection, the download and upload speed should be the same.

I've already tried several things, changed routes, changed the inspection of icmp, tcp, http, https and udp but it doesn't make a difference. Anyone out there who had the same problem and solved it? Or maybe not had it, but can help me with this?

Cheers,

Thijs

[David_Che]

I suspect asymmetric MTU caused the problem.  You can use the ' ping -df x.x.x.x packet_size' to test the maximum MTU on the path. then you can configure 'option tcp adjust-mss maximum_mss' on ASA to avoid bi-directional packet fragment.

[thijs.hemmen]

Thanks David. This could indeed be my problem. I will change the MTU outside business hours and see if I can get it working. I couldn't find the 'option tcp adjust-mss maximum_mss' command. I can remember using it, but not on an ASA. Will changing the MTU for an interface do the same thing -> came to mind because of this article: http://www.cisco.com/c/en/us/td/docs/security/asa/asa92/configuration/general/asa-general-cli/interface-basic.html#pgfId-1887099

Edit: wrong link.

[thijs.hemmen]

I wanted to give, whoever reads this in the future, an update on the problem. I've changed two things so far:

1. got rid of a Cisco 2960 switch which was between the router and the external fiber switch;

2. lowered my outside MTU to 1484 after a test done at http://www.letmecheck.it/mtu-test.php.

After that tests with iPerf show a download bandwith of almost 10MB and more import also for upload!

David, I couldn't figure out how to get the config working with the adjust-mss. Guess the MTU does something now for the upload, but I can't tell for sure.