DNS Server UDP Query Limitation

This script is Copyright (C) 2005-2015 Tenable Network Security, Inc.


Synopsis :

The remote DNS server is not RFC1035 compliant.

Description :

A DNS server is running on this port but it only answers to UDP
requests. This means that TCP requests are blocked by a firewall.

This configuration is not RFC-compliant. Contrary to common belief,
TCP transport is not restricted to zone transfers (AXFR) :

- answers bigger than 512 bytes are always transmitted
over TCP.
- for all other requests, UDP is only 'preferred' for
performance reasons. i.e. RFC1035 (STD0013) does not
forbid a DNS client from issuing its queries directly
over TCP.

See also :

http://www.faqs.org/rfcs/rfc1035.html

Solution :

If you are sure that the DNS server will never return answers bigger
than 512 bytes and that the client software prefers UDP (which is
nearly certain), you may ignore this message.

Risk factor :

None

Family: DNS

Nessus Plugin ID: 18356 (check_dns_tcp.nasl)

Bugtraq ID:

CVE ID:

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