Port 53 is open for DNS. Why would I need this? You need to have UDP 53 allowed for responses to DNS queries that your server sends, as UDP is a stateless protocol. Don't block it if you want any kind of outbound connectivity, software updates, etc. Note that for name resolution software in most modern operating systems that's been patched with DNS source port randomization, the source port of ...

Jun 4, 2014 · Port 53 udp is reserved for DNS traffic. Even though you may have gotten OpenVPN to work on this port you are seriously blocking the server's ability to resolve DNS queries. I would strongly advise you to use a different port, one that is not in use by other services on that machine before even attempting to fix the issues you're seeing.

Nov 8, 2013 · I have what I believe to be an easy question. I want to lock down port 53 for outbound access to 3 of our internal DNS servers so that they're the only hosts that can service requests in the outbound direction. Any other host that attempts to service DNS queries outbound should be blocked. How wo...

May 30, 2020 · Recently both of our DNS servers stopped responding to incoming UDP on port 53, tested with dig and it works with TCP. They both have common ISP. Is there any way to traverse route and find out exa...

Jul 22, 2012 · We have a Cisco ASA 5505 (v7.2 (3)) with a "fairly" normal configuration yet we have a problem where it appears UDP/53 traffic is denied on our inside network. here is output from our sys log: SyslogID Source IP Dest IP Description 305006 172.18.22.3 portmap translation creation failed for udp src inside:172.18.22.156/42013 dst inside:172.18.22 ...

Feb 9, 2018 · Solved: This is the ACL applied inbound on the WAN interface. End user is having problems querying public DNS on UDP/53. 10 deny ip 10.0.0.0 0.255.255.255 any 20 deny ip 172.16.0.0 0.0.15.255 any 30 deny ip 192.168.0.0 0.0.255.255 any (229 matches)

Oct 5, 2012 · Hi I've setup Cisco router's DNS server... via "ip dns server" which in need for inside use.. however now if I do portscan from outside it shows port 53 opened. How do I block all traffic to that 53 port from outside since i need this DNS only …

Dec 17, 2024 · The dns server sits at 157.141.245.10. Initially, i allowed in bound "permit udp <subnet and wc> host 157.141.245.10", but the traffic is still being blocked out to server. So i set "eq domain" and "eq 53" to no success. I've also moved it upwards in the ACL and had no success there either.

Feb 11, 2016 · All inbound UDP traffic for port 53 is blocked, except to the university's own DNS servers? That sounds suspiciously like an attempt at using DNS for censorship to me.

Jun 25, 2012 · Udp for small stuff like asking one address or something like that, and for larger transfers such as zone and so on it will switch to using Tcp. so yes it might work to test with using tcp port 53.