DHCP related questions

[subramaniyakarthic]

1)When I shut down my PC that uses DHCP, it sends the DHCP release and thats fine. But when PC comes back,will it use the same IP.I tried this with connecting two routers over Fastethernet.(one router server,other client).Every time I brought down the link I got a new IP. Can someone explain if this is the right behavior.But in my Laptop I get the same IP whenever I get a DHCP from modem. Is it a cicso behavior to get diff. IPs?

2) In DHCP, when I am tryin to renew the binding after 1/2 total time, will the server send the ACK will the lease time of (T) or (T+1/2T) because I already have a 1/2 T time left in my lease period.

3) How are the IP's in pool being assigned..first IP from the pool available (or) the least recently used?

4)When a server sees a conflict by pinging what does it do to the IP address that was assigned earlier.I makes it part of the ip dhcp binding conflict.But does it remove the IP address assigned and adds it back to pool?

Thanks,

RSK

[skothiya · Accepted solution]

Hi Karthic,

I will answer your questions based on my observation.

1) When a client renews its ip address it has two ways to do it.

a) Send DHCP request (this is generally done) which contains the ip address that is already used by the client.

b) Send DHCP Discover. This will be for a new ip address.

Now if the DHCP server gets a DHCP request and the ip address requested is assigned to the same mac address then the server sends the same ip address.

2) The time will be T. eg. if the lease it 24 hours. and a request is send at 12 hours then after the ack from the server. The lease time will again be 24 hours.

3) During my testing I have always seen next in the index.

eg. the server has ip from 1-10. 1,2,3 have been used up. Assume 1 is freed. Then for the next DISCOVER the server will send 4.

4) Ip is not assigned to pool. It is registered in the conflict database. To return the conflict ip addresses to pool you would have to run " clear ip dhcp conflict [* | specific ip]