Slow downloads with SRX [ Edited ]

[mawr]

Hello everyone,

Since the installation of our SRX I've noticed that HTTP downloads will sometimes start very slow and then increase to the maximum speed of the connection over the course of a few seconds.  Recently though the downloads will sometimes stay at a very low speed until competely restarted.  I've noticed this behavior on Windows XP and Windows 7 machines.

Does anyone know why this might be?

Thanks,

mawr

EDIT: I forgot to mention that I'm running 10.1R2.8 and that I don't have any CoS policies configured.  Thanks.

[Dominik]

Do you have any virus scanning features enabled? What we could also have a look on is the MSS size. You could reduce it a little bit by for example

set security flow tcp-mss all-tcp mss 1350

or even a bit lower.

Regards,

Dominik

[mawr]

I'll give that a shot, thanks Dominik!  Do you also thinking that enabling PMTUD under system internet options would make a difference as well?

[Dominik]

You can of course enable PMTU detection but this is usually already automatically enabled on the client side. It may also be worth to check and double check the correct MTU values, in particular for the WAN side facing interface(s).