While trying to document a network I couldn’t get into a dell powerconnect 2724. Every time I tried to log in I got a “user name or password is missing” error. The switch was in production so I couldn’t try to reset it to defaults and I needed to see the vlan configuration in the first place. I ended up emailing another administrator who I thought had set it up and he replied with a username/password I had tried. A few minutes later he said he had to do it from a machine without Avast installed.
I tried it today and sure enough avast resident protection breaks things. The TCP streams are interesting to take a look at, looks like avast might be throwing a spurious return in the http request so the username and password are being sent in a separate segment. Disabling resident protection makes everything work normal again.
Armed with avast as a search term, it looks like a common problem. The 2748 works fine over http. It does use different post variables and doesn’t appear to bother to encode the passwords. I assume that was base64 encoding on the 2724.