North American Network Operators Group|
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Re: PMTU and Broken Servers
> This is a new problem to me, but I'm sure people have run into it > before. Are the servers really that broken (PMTU enabled, ICMP > Can't Fragement filtered)? Does the head end box of DSL services > generally do something to work around this (ie, clear the DF bit)? > Am I just being an idiot and missing something obvious? This is fairly common, since PMTU-D is generally enabled by deafult, and for better or worse, many folks filter all ICMP, despite the bad effects that can lead to. I've had arguments with customers about their having a broken config, but their unwillingness to believe it because "they haven't changed anything". The only real workaround is to have a minimum MTU of 1500 across your network including all encapsulation.