topic Re: configuring DNS on firewall in Network Security https://community.cisco.com/t5/network-security/configuring-dns-on-firewall/m-p/1217326#M875578 <HTML><HEAD></HEAD><BODY><P>thanks vikram.</P></BODY></HTML> Sat, 28 Feb 2009 03:51:22 GMT Bruce Summers 2009-02-28T03:51:22Z configuring DNS on firewall https://community.cisco.com/t5/network-security/configuring-dns-on-firewall/m-p/1217324#M875570 <P>is it necessary to allow both UDP and TCP port 53 for accessing DNS servers through a firewall access-list?</P> Mon, 11 Mar 2019 14:58:45 GMT https://community.cisco.com/t5/network-security/configuring-dns-on-firewall/m-p/1217324#M875570 Bruce Summers 2019-03-11T14:58:45Z Re: configuring DNS on firewall https://community.cisco.com/t5/network-security/configuring-dns-on-firewall/m-p/1217325#M875575 <HTML><HEAD></HEAD><BODY><P>tcp/53 is used for zone-transfers. if you are doing just normal queries udp/53 will suffice.</P></BODY></HTML> Sat, 28 Feb 2009 03:49:23 GMT https://community.cisco.com/t5/network-security/configuring-dns-on-firewall/m-p/1217325#M875575 vikram_anumukonda 2009-02-28T03:49:23Z Re: configuring DNS on firewall https://community.cisco.com/t5/network-security/configuring-dns-on-firewall/m-p/1217326#M875578 <HTML><HEAD></HEAD><BODY><P>thanks vikram.</P></BODY></HTML> Sat, 28 Feb 2009 03:51:22 GMT https://community.cisco.com/t5/network-security/configuring-dns-on-firewall/m-p/1217326#M875578 Bruce Summers 2009-02-28T03:51:22Z Re: configuring DNS on firewall https://community.cisco.com/t5/network-security/configuring-dns-on-firewall/m-p/1217327#M875580 <HTML><HEAD></HEAD><BODY><P>Here is another reason why tcp/53 is used "A client can use TCP whenever it wants, and has to use TCP when the response it gets via UDP is truncated because it is too long"</P><P></P></BODY></HTML> Sat, 28 Feb 2009 04:03:15 GMT https://community.cisco.com/t5/network-security/configuring-dns-on-firewall/m-p/1217327#M875580 vikram_anumukonda 2009-02-28T04:03:15Z Re: configuring DNS on firewall https://community.cisco.com/t5/network-security/configuring-dns-on-firewall/m-p/1217328#M875583 <HTML><HEAD></HEAD><BODY><P>tcp/53 is also used for large transfers.</P></BODY></HTML> Wed, 04 Mar 2009 16:49:52 GMT https://community.cisco.com/t5/network-security/configuring-dns-on-firewall/m-p/1217328#M875583 duncanm 2009-03-04T16:49:52Z