NAT Does Not Work to Certain Sites

[BarryStiefel]

NAT Does Not Work to Certain Sites



Contributed by BenSmith
Published in geeklog Wednesday, June 25 2003 @ 07:30 PM EST
Published in oldfaq 2003-Mar-21 00:06 dwelchATphoneboyDOTcom

Use a packet sniffer to look for packets larger than MTU with the "do not fragment" bit set. snoop, tcpdump, or the like should be able to find packets like this. Once you determine that, either permit ICMP type-3 code 4 packets to your clients or adjust your MTU. A more detailed discussion of MTU Discovery can be found in RFC-1191.

Another possibility is that you are attempting to access a website that is using the same address space you are using internally and NATting. This is why if you are using non-routable addresses on your internal network, you should strive to use those as defined by RFC-1918 -- they are guaranteed never to be used on the Internet.

-- RayLodato - 14 Jan 2004

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