As the security threats on the Internet are becoming more prevalent, firewalls and other forms of protection are becoming more commonplace. Unfortunately, improperly configured firewalls can cause a variety of problems. One particularly nasty problem is when a firewall administrator chooses to use - or continue using -Path MTU Discovery (a good choice in most situations), but blocks packets required for the protocol to work: ICMP type 3 code 4 packets. This problem, the Path MTU Discovery Black Hole, has been discussed many times before. However with under- 1500 MTU protocols such as PPPoE becoming common for both home and business high-speed connections, this problem is affecting more people than ever before.
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