I am having a nightmare trying to connect my shiny new ASA 5510 to an old Cat 3550 switch. The ASA port shows up/up but receives no packets at all. As soon as I put the cable back in to the old PIX515E it works straight away, making me believe this is a bug between the 5510 and the 3550. I have tried countless combinations of speed/duplex, and I've upgraded both the switch software and ASA software to latest levels. I have even tried a different ASA. The only way I can get the link between the ASA and the switch to come up is to place a "Linksys residential cable router with 4-port switch" in between!!! Clearly the 5510 and 3550 do not like negotiating a link for whatever reason.
Any help will be massively appreciated.