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Problem with large UDP DNS packets through PA DNS Proxy

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Problem with large UDP DNS packets through PA DNS Proxy

EthelTheFrog
L0 Member

‎09-21-2016 08:53 AM

We've been using the PA DNS Proxy for quite some time, until recently we noticed that, for some hosts, we could retrieve an A record but not an MX record (the proxy is feeding our mail servers). Eventually we found that we could get that MX record by changing forwarders for the mail servers directly to our DNS boxes, rather than through the PA DNS Proxy (which is being fed from our DNS boxes), i.e. bypassing the DNS Proxy altogether. It seems that the MX response for this particular host results in a UDP packet that is 539 bytes long (EDNS0, of course), which is bigger than the 512 bytes normally allowed for UDP DNS packets (yes, it's definitely UDP, not TCP). Has anyone else seen this problem?

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