Blocking AOL Instant Messenger

[BarryStiefel]

Blocking AOL Instant Messenger



AIM will use any available port that is allowed through the firewall. The Auto Configure option on the AIM client will use just about anything, including DNS and HTTP. The only surefire way to lock out access to it is to block all access to the host login.oscar.aol.com. However, this DNS resolves to more than one IP and it changes. You should verify this with an nslookup. You need to block all traffic to these IPs. You should also disable the rulebase properties for DNS as, sure enough, it will use these ports.

Here are a few IPs that are known to belong to login.oscar.aol.com:

• AOLim_1 = 152.163.214.75
• AOLim_2 = 152.163.214.76
• AOLim_3 = 152.163.214.108
• AOLim_4 = 152.163.214.109
• AOLim_5 = 205.188.1.56
• AOLim_6 = 205.188.4.106
• AOLim_7 = 205.188.147.114
• AOLim_8 = 152.163.241.121
• AOLim_9 = 152.163.241.129
• AOLim_10 = 152.163.242.28
• AOLim_11 = 152.163.242.24
• AOLim_12 = 152.163.241.120
• AOLim_13 = 152.163.241.128
• AOLim_14 = 152.163.241.96
• AOLim_15 = 64.12.161.153
• AOLim_16 = 64.12.161.185

The Smart Defense HTTP worm catcher in NG FP3 is pretty useful at stopping illicit AOL and MS Instant Messenger on 80. Add these lines:

MS-IM gateway.dll? AIM :20480/

I picked these apparently unique strings out of http headers shown up by plonking an http resource on miscreants source addresses. As far as I can tell, the method works 100%. Another means to block both AOL/ICQ/Y! and MSN is to use IM Firewatcher. They have a free version, requires a few minutes to set up. Good news is that they have automatic updates, bad news is that it does not work with Gigagbit NICs



-- GuyR - 15 Jan 2004

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