DHCP on Cisco routers - Couple of quick Qs

[James Hardman]

Hello,

I have a couple of queries in regards to the DHCP service on Cisco routers.

1 - If you have a DHCP pool configured on a router and also a ip-helper address pointing to DHCP server, what would the router do with a DHCP request?  Would it use it's own pool to allocate an IP address, or would it send the traffic to the DHCP server.  (i.e. which takes precedence) ?

2 - Also, if there are two routers on your LAN both with DHCP pools (RouterA - 192.168.1.2 - 127, RouterB 192.168.1.128 - 253).  What happens when one of the routers exhausts it's address pool?  Does it stop responding to the PC and the other router continues to respond to the DHCP requests?

3 - When a Cisco router is going to allocate an IP address to a device on the LAN that has requested an address, before it allocates the next address in it's DHCP pool, what checks does it do on the LAN?  i.e. does it conduct and gratuitous ARP? Does it perform a ping against this IP to see if anything responds to ensure that it won;t create a duplicate address on the LAN?

Thanks for any input.

Jimmy

[Surendra BG]

1 - If you have a DHCP pool configured on a router and also a ip-helper address pointing to DHCP server, what would the router do with a DHCP  request?  Would it use it's own pool to allocate an IP address, or would  it send the traffic to the DHCP server.  (i.e. which takes precedence) ?

ANS

I guess the Local takes the precedence.. havnt tried it though..

2 - Also, if there are two routers on your LAN both with DHCP pools  (RouterA - 192.168.1.2 - 127, RouterB 192.168.1.128 - 253).  What  happens when one of the routers exhausts it's address pool?  Does it  stop responding to the PC and the other router continues to respond to  the DHCP requests?

ANS -

NO, this means there are 2 different interface vlans..

3.When a  Cisco router is going to allocate an IP address to a device on the LAN  that has requested an address, before it allocates the next address in  it's DHCP pool, what checks does it do on the LAN?  i.e. does it conduct  and gratuitous ARP? Does it perform a ping against this IP to see if  anything responds to ensure that it won;t create a duplicate address on  the LAN?

ANS

The server detects conflicts using ping. The  client detects conflicts using gratuitous Address Resolution Protocol  (ARP). If an address conflict is detected, the address is removed from  the pool and the address will not be assigned until an administrator  resolves the conflict.

Lemme know if this answered your question..

Regards
Surendra