Brocade FastIron Ethernet Switch Layer 3 Routing Configuration Guide - Manual (Page 86)

the requested time and tries to return the same network address each time the client makes a request.
The period of time for which a network address is allocated to a client is called a lease. The client may
extend the lease through subsequent requests. When the client is done with the address, they can
release the address back to the server. By asking for an indefinite lease, clients may receive a
permanent assignment.
In some environments, it may be necessary to reassign network addresses due to exhaustion of the
available address pool. In this case, the allocation mechanism reuses addresses with expired leases.
Configuration notes for DHCP servers
• DHCP server is supported in the Layer 2 and Layer 3 software images.
• In the event of a controlled or forced switchover, a DHCP client will request from the DHCP server
the same IP address and lease assignment that it had before the switchover. After the switchover,
the DHCP Server feature will be automatically re-initialized on the new active controller or
management module.
• For DHCP client hitless support in an IronStack, the stack mac command must be used to
configure the IronStack MAC address, so that the MAC address does not change in the event of a
switchover or failover. If stack mac is not configured, the MAC address/IP address pair assigned to
a DHCP client will not match after a switchover or failover. Furthermore, in the Layer 3 router
image, if the stack mac configuration is changed or removed and the management port has a
dynamic IP address, when a DHCP client tries to renew its lease from the DHCP server, the DHCP
server will assign a different IP address.
• If any address from the configured DHCP pool is used, for example by the DHCP server, TFTP
server, etc., you must exclude the address from the network pool. For configuration instructions,
refer to
Specifying addresses to exclude from the address pool on page 93.
• Ensure that DHCP clients do not send DHCP request packets with Maximum Transmission Unit
(MTU) larger than 1500 bytes. Brocade devices do not support DHCP packets with MTU larger than
1500 bytes.
DHCP Option 82 support
The DHCP relay agent information option (DHCP option 82) enables a DHCP relay agent to include
information about itself when forwarding client-originated DHCP packets to a DHCP server. The DHCP
server uses this information to implement IP address or other parameter-assignment policies.
In a metropolitan Ethernet-access environment, the DHCP server can centrally manage IP address
assignments for a large number of subscribers. If DHCP option 82 is disabled, a DHCP policy can only
be applied per subnet, rather than per physical port. When DCHP option 82 is enabled, a subscriber is
identified by the physical port through which it connects to the network.
DHCP Server options
A FastIron configured as a DHCP server can support up to 1000 DHCP clients, offering them the
following options:
• NetBIOS over TCP/IP Name Server - Specifies a list of RFC1001/1002 NBNS name servers listed
in order of preference.
• Domain Name Server - Specifies a list of Domain Name System (RFC 1035) name servers
available to the client. Servers are listed in order of preference.
• Domain Name - Specifies the domain name the client should use when resolving hostnames using
the Domain Name system.
• Router Option - specifies a list of IP addresses for routers on the client subnet. Routers are listed
in order of preference.
• Subnet Mask - Specifies the client subnet mask (per RFC950).
Configuration notes for DHCP servers
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