Is my dynamic IP always changing?

[Naruto]

I have a dynamic IP through my sbc dsl. I am using a router to connect all my computers to the internet. I have my router option "idle timeout" set to 0, meaning it never times out with the isp unless it loses connection. So does that mean that when I log onto the internet, the dynamic ip assigned to me stays the same until my router loses connection? I like to have dynamic ip simply because i feel more secure which a alternating ip rather than a static ip.

 

[subflava]

It all depends on the lease time set by your ISP. Even when you set the idle time to 0, your IP will still change according to the lease time.

 

[Nothinman]

It all depends on the lease time set by your ISP. Even when you set the idle time to 0, your IP will still change according to the lease time.

Not necessarily true, my ISP has my lease time set for like a week and I've had the same IP for about a year. It all depends on your DHCP client and how strict your ISP is, if your DHCP client is any good it'll request a lease renewal when the lease is about half up and if the DHCP server isn't set to force an IP change it'll grant the renewal every time.

 

[spidey07]

Originally posted by: Nothinman

It all depends on the lease time set by your ISP. Even when you set the idle time to 0, your IP will still change according to the lease time.

Not necessarily true, my ISP has my lease time set for like a week and I've had the same IP for about a year. It all depends on your DHCP client and how strict your ISP is, if your DHCP client is any good it'll request a lease renewal when the lease is about half up and if the DHCP server isn't set to force an IP change it'll grant the renewal every time.

yep - standards say renew at half lease time. when you lease an IP address the server say "this is your IP for the duration of the lease"

so depending on the DHCP server/lease time you could always have the same IP. Now if you turned your router off for greater than lease time then you "might" get a different one.

Also as stated above it has nothing to do with traffic.

 

[subflava]

Hmm...I suppose there is no simple mechanism to force your computer to renew its IP address. But then what happens if I get an IP from the DHCP server, then set that IP statically on my device?

I suppose what would happen is the DHCP server would expire the lease due to a lack of any further DHCP client renewal requests being received. Then I guess you have your switch disable any ports that do not have active DHCP leases associated with them?

If the above is true, then I guess it's up to the policy on the DHCP server whether or not it wants to renew leases for a particular IP.

 

[spidey07]

suppose what would happen is the DHCP server would expire the lease due to a lack of any further DHCP client renewal requests being received. Then I guess you have your switch disable any ports that do not have active DHCP leases associated with them?

that's exactly how it works. The server simply says "you can have this IP for this period, if I don't hear back from you then it goes back into the pool for others to use, you greedy bastage."

well, it doesn't really say greedy bastage, but he's ticked off because you didn't even have the decency to "release" the address and just left him hanging.

 

[Nothinman]

Hmm...I suppose there is no simple mechanism to force your computer to renew its IP address. But then what happens if I get an IP from the DHCP server, then set that IP statically on my device?

There's no mechanism because just about every client does it already at half expiration. If you set it statically it'll work fine, but you might cause some network problems if their DHCP server isn't smart enough to check addresses before handing them out or if you block ping requests. The ISC DHCP server pings an address before giving it out to make sure it doesn't cause a dup, but if they use a server that doesn't or you don't reply to pings you risk duping yourself.

If the above is true, then I guess it's up to the policy on the DHCP server whether or not it wants to renew leases for a particular IP.

Basically, yes. If the server doesn't want to renew the lease it sends a DHCPNAK and the client is supposed to fall back to DHCPDISCOVER messages to get a new lease.

 

[imported_Paladin]

Originally posted by: Naruto
I have a dynamic IP through my sbc dsl.

I have SBC DSL, So Cal, and every time I reboot the modem I get a different IP.

I am using a router to connect all my computers to the internet. I have my router option "idle timeout" set to 0, meaning it never times out with the isp unless it loses connection. So does that mean that when I log onto the internet, the dynamic ip assigned to me stays the same until my router loses connection?

Yes. (Except it is when your router logs into your ISP that the IP is set. You do not log onto the Internet.)

I like to have dynamic ip simply because i feel more secure which a alternating ip rather than a static ip.

You get your IP from your router. Your router has the public IP and it is the router that would be subjected to any hack attempts. AFAIK, a dynamic IP is no protection against trojans and viruses.