A DHCP pool is a configured set of IP addresses and client parameters that a Cisco IOS DHCP server leases to hosts. The pool defines an address range and can provide the default gateway, DNS servers, domain name, and lease duration. section 4.1.2 section 4.4
Address exclusions reserve selected addresses outside the leasable set, commonly for statically configured servers. Excluding the network address, broadcast address, or router address is unnecessary because the router does not lease them. section 4.1.2
Configure the pool and its client settings with these Cisco IOS commands:
- Use ip dhcp pool name to enter DHCP pool configuration mode. section 4.4
- Use network network-address {netmask | /prefix-length} to define the addresses available for leasing. section 4.1.2 section 4.4
- Use default-router, dns-server, and domain-name to supply clients with gateway, DNS, and domain parameters. section 4.1.2 section 4.4
- Use lease days hours minutes or lease infinite to set duration; the default lease period is 24 hours. section 4.4
A basic address pool
R1(config)# ip dhcp excluded-address 10.0.0.2 10.0.0.5 R1(config)# ip dhcp pool POOL1 R1(dhcp-config)# network 10.0.0.0 /24 R1(dhcp-config)# default-router 10.0.0.1 R1(dhcp-config)# dns-server 10.0.0.1 8.8.8.8 R1(dhcp-config)# domain-name jeremysitlab.com R1(dhcp-config)# lease 0 5 30 This reserves four addresses, then leases addresses from the 10.0.0.0/24 network with gateway, DNS, domain, and a five-hour-thirty-minute lease.
Verify active leases with show ip dhcp binding. Cisco IOS pings a selected address before offering it; a responding address is marked conflicted and removed from assignment until the conflict is resolved and cleared. section 4.4
Use show ip dhcp conflict to inspect conflicts, clear ip dhcp conflict {* | ip-address} to remove conflict records, and clear ip dhcp binding {* | ip-address} to remove active bindings. section 4.4
A multilayer switch can provide separate pools for management, internal, and guest VLANs. Each pool maps its subnet to a default gateway and can carry DHCP options such as option 42 for NTP and option 43 for a WLC address. section 21.1.1
