
SNMP, RMON, BootP, DHCP, and RARP Concepts
117362-A Rev. A 2-29
2. If the router accepts the packet, it alters the packet by:
• Incrementing the hops field by 1
• Writing the IP address of the input interface to the gateway IP address
field
3. The router then determines which networks should receive this packet and
broadcasts it to other networks through a forwarding route that you specify
when you configure the router for BootP services.
If the BootP packet has to travel to a network through another router, you
must specify the forwarding route using one of the following methods:
• Configure the second router for BootP services.
In this case, the second router inspects the packet in the same way as the
first router, and increments the hops field by 1. The second router will not,
however, replace the address in the gateway IP address field, because
servers will reply to the first router that received the BOOTREQUEST
packet.
• Configure the first router to forward the BOOTREQUEST packet to a
specific server.
In this case, the router will unicast the BOOTREQUEST packet to the
server through normal IP services.
4. Servers on other networks receive the BOOTREQUEST packet and respond
with a BOOTREPLY packet. Those servers transmit the BOOTREPLY
packets through normal IP services to the address of the first interface that
received the BOOTREQUEST packet. That address appears in the gateway IP
address field in the BOOTREQUEST packet.
5. When the router that first received the BOOTREQUEST packet receives the
BOOTREPLY packet, it examines the gateway IP address field to check that
the value in this field is the same as the IP destination address that the server
used for the packet. If the addresses differ, the router discards the
BOOTREPLY packet.
6. If the router accepts the packet, it examines the flags field and forwards the
packet to the client as follows:
• If the flags field contains the value 1, the client does not know its own IP
address. The router broadcasts the BOOTREPLY packets to the IP
broadcast address (255.255.255.255).
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