59-9
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Chapter 59 Configuring the Cisco IOS DHCP Server
How to Configure the Cisco IOS DHCP Server
You can configure the DHCP server to ignore and not reply to any BOOTP requests that the server
receives. This functionality is beneficial when there is a mix of BOOTP and DHCP clients in a network
segment and there is a BOOTP server and a Cisco DHCP server servicing the network segment. The
BOOTP server is configured with static bindings for the BOOTP clients and the BOOTP clients must
obtain their addresses from the BOOTP server. However, DHCP servers can also respond to BOOTP
requests and the DHCP server may offer an address that causes the BOOTP clients to boot with the
address from the DHCP server, instead of the address from the BOOTP server. Configuring the DHCP
server to ignore BOOTP requests ensures that the BOOTP clients will receive address information from
the BOOTP server and will not accept an address from a DHCP server.
Cisco software can forward these ignored BOOTP request packets to another DHCP server if the
ip
helper-address
command is configured on the incoming interface.
Static Route with the Next-Hop Dynamically Obtained Through DHCP
Static routes are updated in the routing table when the default gateway is assigned by the DHCP server.
These routes remain in the routing table until the DHCP lease expires and then the routes are removed.
When a DHCP client releases an address, the corresponding static route (the route configured using the
ip route
command) is automatically removed from the routing table. If the DHCP router option (option
3 of the DHCP packet) changes during the client renewal, the DHCP default gateway changes to the new
IP address supplied after the renewal.
This feature is particularly useful for VPN deployments such as Dynamic Multipoint VPNs (DMVPNs).
It is useful when a nonphysical interface, such as a multipoint generic routing encapsulation (mGRE)
tunnel, is configured on a device and certain traffic must be excluded from entering the tunnel interface.
Note
•
If the DHCP client is not able to obtain an IP address or the default device IP address, the static route
is not installed in the routing table.
•
If the lease has expired and the DHCP client cannot renew the address, the DHCP IP address
assigned to the client is released and any associated static routes are removed from the routing table
How to Configure the Cisco IOS DHCP Server
•
Configuring a DHCP Database Agent or Disabling Conflict Logging, page 59-10
•
Excluding IP Addresses, page 59-10
•
Configuring Manual Bindings, page 59-17
•
Configuring the DHCP Server to Read a Static Mapping Text File, page 59-18
•
Customizing DHCP Server Operation, page 59-19
•
Configuring a Remote Device to Import DHCP Server Options from a Central DHCP Server,
page 59-19
•
Configuring DHCP Address Allocation Using Option 82, page 59-21
•
Configuring Static Route with the Next-Hop Dynamically Obtained Through DHCP, page 59-23
•
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