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telnet to port 53

gusy just want to check the DNS server attached to the firewall can i tried to telnet to port 53 on a roiuter just to see if the remote firewall alllows the conection.......telnet is tcp and DNS is udp based will it work thanks

  • Firewalling
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Cisco Employee

telnet to port 53

If you are trying to see if connectivity works on DNS request (normally uses UDP/53), then the answer is no, telnet on port 53 will not work.

If you are trying to test DNS resolution/request, then just use "nslookup" from command prompt, then specify the dns server: server , then test the resolution: cisco.com

Example from DOS prompt:

C:\Windows\System32>nslookup

> server 4.2.2.2

Default Server:  vnsc-bak.sys.gtei.net

Address:  4.2.2.2

> cisco.com

Server:  vnsc-bak.sys.gtei.net

Address:  4.2.2.2

Non-authoritative answer:

Name:    cisco.com

Addresses:  2001:420:1101:1::a

          198.133.219.25

Gold

Re: telnet to port 53

No but yes it might.

You can not "mix" udp and tcp, they are totally different protocols so you are using one or the other.

you can not test one of them with the other.

However DNS use BOTH Udp and Tcp so it listens on both protocols.

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.

VIP Purple

telnet to port 53

Not directly related to your problem, but perhaps helpful:

When testing connections to remote servers, NetCat is much more powerfull than using Telnet for this kind of work.

-- Don't stop after you've improved your network! Improve the world by lending money to the working poor: http://www.kiva.org/invitedby/karsteni
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