User`s guide

66 XSR User’s Guide
General IP Features Chapter 5
Configuring IP
NOTE
The XSR supports a total of 516 dynamic ARP entries, 128 ARP requests
pending, and 200 static ARP entries with the standard memory of 64
MBytes installed.
BOOTP/DHCP Relay
The Bootstrap Protocol (BOOTP) is used by systems with no capability of
learning their IP addresses. BOOTP requests can be forwarded by routers, not
necessitating one server on each physical network. Normally, BOOTP/DHCP
requests are not forwarded, since they are local broadcasts which are not
designed to be forwarded, and they have an invalid nonroutable IP source
address, such as 0.0.0.x. But the agent replaces the destination address with a
helper address, and the source address with its own address, then forwards it.
You can set the helper address with the
ip helper-address command.
When a BOOTP/DHCP response is received, the packet is sent to the
requester as a unicast IP packet, according to RFC-951, with clarifications in
RFC-1532.
NOTE
The XSR supports a total of 50 IP helper addresses per interface and 50 IP
(UDP) forward ports with standard memory (64 MBytes) installed.
Broadcast
A broadcast is a packet destined for all hosts on a given network as defined
by RFC-919 and RFC-922.
Directed Broadcast
An IP directed broadcast is a datagram sent to the broadcast address of a
subnet to which the sending device is not directly attached. The directed
broadcast is routed through the network as a unicast packet until it arrives at
the target subnet, where it is converted into a link-l
ayer broadcast.