Beware NIC and Switch Autonegotiation
I’ve made the point here many times – you need to manually configure the ISA Firewall’s NICs so that they don’t use autonegotiation with its connected switches. Failure of autonegotiation to complete correctly will cause difficult to troubleshoot performance problems that the misinformed “network guy” will attribute to the ISA Firewall.
You can quickly beat down the “network guy” and show that he doesn’t know what he’s talking about when you hard code the NIC’s speed and duplex parameters. This will improve your standing in the ranks and let the rest of the staff know that network guys should stick to routing protocols and stay away from network security 
For a great detailed discussion of this issue, check out Jim Harrison’s review of autonegotiation at:
http://blogs.technet.com/isablog/default.aspx
HTH,
Tom
Thomas W Shinder, M.D.
Site: www.isaserver.org
Blog: http://blogs.isaserver.org/shinder/
Book: http://tinyurl.com/3xqb7
Email: tshinder@isaserver.org
MVP — Microsoft Firewalls (ISA)
Thomas Shinder Blog » Blog Archive » More Information About NIC Autoconfiguration: Gigabit NICs Says:
October 18th, 2006 at 6:58 am
[…] I just thought I would share this with you guys, I know there was some confusion on this a while back and Tom just posted on his blog regarding “Beware NIC and Switch Autonegotiation” . Most network engineers are under the impression that you should always force or manually configure links for the designated speed/duplex. Unfortunately with the advent of 1000B-TX that is no longer an option. Although Cisco in their infinite wisdom decided to still make it an option in the IOS, it still does the autoneg because it has to. At least according to the IEEE standard. Below is some decent documentation that I found on a Sun site believe it or not. Let me know if you still have questions. […]