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I'm finding out the proper MTU (Maximum Transfer Unit) size of a mail server using this guide. However, the server blocks pings. Is there any other ways I can determine the MTU size without admin access to the mail server?

George
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1 Answers1

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You are trying to do path MTU discovery.

As long as no firewalls on the way block all ICMP traffic (because returning "Fragmentation needed" ICMP packeges have to reach you), the method provided will work with IP packages of all kind. You would just have to send IP packages with the 'DF' flag set and watch for returning "Fragmentation needed" ICMP packages.

Here is a example in python using raw sockets.

tnull
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