Dhcp Relay And Dhcpv6 Relay - Alcatel-Lucent 7705 Configuration Manual

Home computers in a residential high-speed Internet application typically use the DHCP
protocol to have their IP address assigned by their Internet service provider.
The 7705 SAR can act as a DHCP client, a DHCP Relay agent, or a local DHCP server.
When used as a CPE, the 7705 SAR can act as a DHCP client to learn the IP address of the
network interface. Dynamic IP address allocation is supported on network interfaces only.
System interfaces must be configured manually.
OSPF, IS-IS, or RIP is used to advertise the system IP address over the network interface to
the next-hop router. Static routing cannot be used because the network interface IP address is
dynamic and can change during normal operation.
The DHCP protocol requires the client to transmit a request packet with a destination address
of 255.255.255.255 (broadcast) that is processed by the DHCP server. Since IP routers do not
forward broadcast packets, this would suggest that the DHCP client and server must reside
on the same network segment. However, for various reasons, it is sometimes impractical to
have the server and client reside in the same IP network.
When the 7705 SAR is acting as a DHCP Relay agent, it processes these DHCP broadcast
packets and relays them to a preconfigured DHCP server. Therefore, DHCP clients and
servers do not need to reside on the same network segment.
When the 7705 SAR is acting as a local DHCP server, it processes these DHCP broadcast
packets and allocates IP addresses for the DHCP client as needed.
The 7705 SAR supports a maximum of 16 servers per node on the 7705 SAR-8 with a
CSMv1, and on the 7705 SAR-A, 7705 SAR-F, 7705 SAR-H, 7705 SAR-Hc, 7705 SAR-M,
7705 SAR-W, and 7705 SAR-Wx. The 7705 SAR supports a maximum of 62 servers per
node on the 7705 SAR-8 with a CSMv2 and on the 7705 SAR-18. Any Layer 3 interface
configured using the global routing table or Layer 3 services supports up to 8 servers.

DHCP Relay and DHCPv6 Relay

The 7705 SAR provides DHCP/BOOTP Relay agent services and DHCPv6 Relay agent
services for DHCP clients. DHCP is used for IPv4 network addresses and DHCPv6 is used
for IPv6 network addresses. Both DHCP and DHCPv6 are known as stateful protocols
because they use dedicated servers to maintain parameter information.
In the stateful autoconfiguration model, hosts obtain interface addresses and/or configuration
information and parameters from a server. The server maintains a database that keeps track
of which addresses have been assigned to which hosts.
The 7705 SAR supports DHCP Relay on the base router, and on access IP interfaces
associated with IES and VPRN. Each DHCP instance supports up to 8 DHCP servers.
7705 SAR OS Router Configuration Guide
IP Router Configuration
33