HP-UX IP Address and Client Management Administrator's Guide HP-UX 11i v2, HP-UX 11i v3

the maximum hop value configured for this client on a BOOTP server, the bootrequest
is dropped. The hops value limits the number of times a bootrequest can be relayed.
• It sets the secs field of the bootrequest packet to 0 for a first-time request. If the client
does not receive a reply to this request, it sets the value of this field to the number of
seconds since the first request was sent. If the value of the secs field is less than the
threshold value configured for this client on a BOOTP server, the bootrequest is dropped.
The threshold value ensures that sufficient time is allowed for a bootreply to be received
by the client before a subsequent bootrequest for the same client is relayed.
• It sets the giaddr (gateway IP address) field to 0. If a BOOTP server finds that this field
is 0, and the client request is to be relayed, then the BOOTP server fills the giaddr field
with its own IP address.
2. The client broadcasts the bootrequest packet on its first LAN interface (lan0). The bootrequest
also contains the client’s hardware address, and, if known, its IP address.
3. The BOOTP server detertimes whether boot information for the client exists in its database.
If boot information for the client is available in the server’s database, the server answers the
bootrequest with a bootreply packet.
4. If the BOOTP server does not find boot information for the client in its database, the BOOTP
server determines whether relay information for the client is available in its database. If the
relay information is not available for the client in the database, the bootrequest is dropped.
If relay information is available and the relay function is enabled for the client, the server
checks the following:
• If the hops value in the bootrequest packet exceeds the maximum configured for the
client, the request is dropped else the hops field in the bootrequest is incremented.
• If the secs value in the bootrequest packet is less than the threshold value configured
on the server for the client, the request is dropped.
If the request is not dropped during the previous checks, the server relays the bootrequest
to the BOOTP servers that are configured for the client. If the giaddr field of the bootrequest
packet is 0, the server enters its IP address in the field.
Steps 3 and 4 are repeated until either the bootrequest is received by a BOOTP server that finds
boot information about the client in its database, or the request is dropped.
When a server finds client information about a particular client in its database, the server answers
the bootrequest with a bootreply packet. The client’s IP address is placed into a field in the
bootreply. The bootreply can also contain the boot file name, which the client must load with
TFTP. Other information that the bootreply can contain include the client’s subnet mask, the
addresses of nameservers, and the addresses of gateways.
If the bootrequest is relayed to one or more BOOTP servers, the bootreply is sent to the IP address
in the giaddr field, which is the IP address of the BOOTP server that initially relayed the
bootrequest. This BOOTP server sends the bootreply to the client.
Figure 1-2 shows a typical example of a bootrequest relay.
Figure 1-2 Bootrequest Relay Example
BOOTP and TFTP Overview 43