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About

Mark
Premium
join:2001-11-15
Phoenix, AZ
kudos:1

DNS - Port 53

Port 53 is used for DNS (Dynamic Name Resolution). This is the service that translates a domain name into a usable IP address. Most likely you do not need to be running this. If you have this port open, you should check if you are running BIND (Linux/Unix based systems only), a service known for its security flaws.

RMD443

@sympatico.ca

Re: DNS - Port 53

Actually, DNS stands for "Domain Name Service", not Dynamic Name Resolution

Mark
Premium
join:2001-11-15
Phoenix, AZ
kudos:1

Re: DNS - Port 53

Sorry, I was pretty tired when I wrote that and I cannot seem to edit my post at the moment. There's no 'R' in DNS anyway. Thanks for pointing that out.

gwion
wild colonial boy
Premium,ExMod 2001-08
join:2000-12-28
Pittsburgh, PA
kudos:1

See also, UDP port 53...

Typically, you will not need to allow TCP connections to or from remote port 53, unless you are using specific applications that query nameservers directly.
--
"Anger makes dull men witty, but it keeps them poor."
Elizabeth I, in Francis Bacon, Apophthegms, 1625

PetePuma
How many lumps do you want
Premium,MVM
join:2002-06-13
Arlington, VA

Re: See also, UDP port 53...

said by gwion:
Typically, you will not need to allow TCP connections to or from remote port 53, unless you are using specific applications that query nameservers directly.

No, you really need both. Normally, replies to DNS requests will come over UDP port 53, as stated above. However, if the reply size is greater than the size of a single UDP packet, the response will instead come via TCP port 53, even for "normal" requests from applications.
briantf

join:2002-08-15
Visalia, CA

DNS servers must have port 53 tcp and udp open

An SMTP mx lookup uses tcp, normal resolver lookups use udp. If you're hosting a server with active zones, you must have both tcp and udp open (unless you've not got mx records).

Resolver (client) requests go out over port 1005 on Win2K boxes. I don't recall if that's standard resolver behavior or not.
blank8

join:2003-12-14
Berkeley, CA

how to block port 53

Would you know how to block port 53.
acsservice

join:2005-06-02
Traverse City, MI

Blocking ports

I assume from the scope of these questions that most are newbies scrounging for answers to basic questions. Blocking of ports is accomplished most simply for you newbies with a firewall device. Alpha makes one for less than $100 and is bullet-proof. For sophisticated management you might want to utilize a proxy server software available in all flavors and prices, which give you almost infinite configurability

... clicks from the walker as I leave
koolwebs

join:2001-04-09
Opa Locka, FL
Zonelabs.com has a free firewall that works well

also analox.com has a port router diverter also free that one can router 53 or any port to a port never used.

xlaserx

@telia.com
Ok somehow my java doesn't work. And i assume that it has something to do with port 53 since it takes care of the names -> IP

Anyone know what this might be?

java.net.UnknownHostException: runescape.com
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:177)
at java.net.Socket.connect(Socket.java:507)
at java.net.Socket.connect(Socket.java:457)
at sun.net.NetworkClient.doConnect(NetworkClient.java:157)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:365)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:477)
at sun.net.www.http.HttpClient.<init>(HttpClient.java:214)
at sun.net.www.http.HttpClient.New(HttpClient.java:287)
at sun.net.www.http.HttpClient.New(HttpClient.java:299)
at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLC
onnection.java:792)
at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConne
ction.java:744)
at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection
.java:669)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLCon
nection.java:913)
at java.net.URL.openStream(URL.java:1007)
at ServerList.grabData(ServerList.java:70)
at ServerList.updateServers(ServerList.java:51)
at Bot.<init>(Bot.java:121)
at Bot.main(Bot.java:95)
Exception in thread "main" java.lang.IllegalArgumentException: n must be positiv
e
at java.util.Random.nextInt(Random.java:248)
at AccessorMethods.random(AccessorMethods.java:3134)
at ServerList.randomServer(ServerList.java:30)
at Bot.<init>(Bot.java:122)
at Bot.main(Bot.java:95)

D_CARR

@nrockv01.md.comcast.

Re: Java through port 53? - We were all newbies

All,

I know it feels good when we achieve knowledge about this domain, but remember we were all newbies. It only shows a weakness of character for someone to lash out and make someone feel bad about the fact they happen to not be an expert. It serves no purpose other then to create bad feelings, not the goal of this excellent site.

Damon
Phatorian

join:2004-09-20
Kingwood, TX
...I've been an IT/PC professional for 15 years and there are always areas I find to feel newb about. It's impossible to know everything about all the areas, as they are constantly changing, so we are all newbs in some areas of IT. The key is knowing where to find the correct answers, like this site.