How can I tell if I have static or dynamic IP Address?

Question

Maybe a stupid question but how can I tell if I have a static IP address or a dynamic IP address? Running Fedora-13

Solution 1

Asking the ISP or network administrator or physically checking the settings is the easiest way because:

If you are talking about the address provided by your ISP, then switching your router off for a while will eventually force the ISP to release your old IP. Unfortunately, you could be unlucky and your "new" IP may be exactly the same as your old one. This means that switching off your router for a while is not a 100% foolproof way of finding out if your IP is static or dynamic. It usually works, though.

If you are talking about your LAN IP then check your router and see if it is selected to provide an IP from a static table or through DHCP, if it's DHCP then you may still end up with the same IP depending on how long the router remembers an IP address allocation before releasing it. Most domestic routers seem to keep them forever, despite the settings.

Solution 2

For public IP addresses, some sites such as WhatIsMyIPAddress.com^† claim their databases can tell if your IP address is static or dynamic.

Also, sometimes running a dig -x your-ip-address might reveal a DNS name that includes some hints from your provider, like dyn prefixes. It's all not standardized though, so indeed the best bet is to get that information from your provider.

^{† In my case the answer is correct; see the "Additional IP Details" button.}

Comments

[Ramy]

thanks for the answers, guys. I'll try some of these out tonight.

[Ramy]

here is my output, do you see any clues? ; <<>> DiG 9.7.1-P2-RedHat-9.7.1-2.P2.fc13 <<>> -x 66.30.118.173 ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 9999 ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;173.118.30.66.in-addr.arpa. IN PTR ;; ANSWER SECTION: 173.118.30.66.in-addr.arpa. 86400 IN PTR c-66-30-118-173.hsd1.ma.comcast.net. ;; Query time: 47 msec ;; SERVER: 192.168.1.1#53(192.168.1.1) ;; WHEN: Mon Nov 29 19:56:54 2010 ;; MSG SIZE rcvd: 93

[Arjan]

@Ramy, the part c-x-x-x-x.hsd1.ma.comcast.net is the DNS name that your provider has assigned. Apart from maybe C=Cable, HSD=High Speed Data and MA=Massachusetts, no clues there (though Comcast wants it for 3rd party email). Using "Additional IP Details" for your IP address gets you to whatismyipaddress.com/ip which claims: ISP: Comcast Cable, Type: Broadband, Assignment: Dynamic IP`. Not 100% accurate, but I guess it's true: their website only seems to mention static IP addresses for business tier subscriptions.

[Ale]

for my dynamic IP (changes every 2-3 days), whatismyipaddress.com says "static", so it's definitely not always accurate. but I think that their guess for Comcast is correct.