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7.3. Server Receives BOOTREQUEST Connected: An Internet Encyclopedia
7.3. Server Receives BOOTREQUEST

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Next: 7.4. Server/Gateway Receives BOOTREPLY

7.3. Server Receives BOOTREQUEST

7.3. Server Receives BOOTREQUEST

[UDP checksum.] If the UDP destination port does not match the 'BOOTP server' port, discard the packet.

If the server name field (sname) is null (no particular server specified), or sname is specified and matches our name or nickname, then continue with packet processing.

If the sname field is specified, but does not match 'us', then there are several options:

  1. You may choose to simply discard this packet.

  2. If a name lookup on sname shows it to be on this same cable, discard the packet.

  3. If sname is on a different net, you may choose to forward the packet to that address. If so, check the 'giaddr' (gateway address) field. If 'giaddr' is zero, fill it in with my address or the address of a gateway that can be used to get to that net. Then forward the packet.

If the client IP address (ciaddr) is zero, then the client does not know its own IP address. Attempt to lookup the client hardware address (chaddr, hlen, htype) in our database. If no match is found, discard the packet. Otherwise we now have an IP address for this client; fill it into the 'yiaddr' (your IP address) field.

We now check the boot file name field (file). The field will be null if the client is not interested in filenames, or wants the default bootfile. If the field is non-null, it is used as a lookup key in a database, along with the client's IP address. If there is a default file or generic file (possibly indexed by the client address) or a fully-specified path name that matches, then replace the 'file' field with the fully-specified path name of the selected boot file. If the field is non-null and no match was found, then the client is asking for a file we dont have; discard the packet, perhaps some other BOOTP server will have it.

The 'vend' vendor-specific data field should now be checked and if a recognized type of data is provided, client-specific actions should be taken, and a response placed in the 'vend' data field of the reply packet. For example, a workstation client could provide

an authentication key and receive from the server a capability for remote file access, or a set of configuration options, which can be passed to the operating system that will shortly be booted in.

Place my (server) IP address in the 'siaddr' field. Set the 'op' field to BOOTREPLY. The UDP destination port is set to 'BOOTP client'. If the client address 'ciaddr' is nonzero, send the packet there; else if the gateway address 'giaddr' is nonzero, set the UDP destination port to 'BOOTP server' and send the packet to 'giaddr'; else the client is on one of our cables but it doesnt know its own IP address yet --use a method described in the 'Egg' section above to send it to the client. If 'Egg' is used and we have multiple interfaces on this host, use the 'yiaddr' (your IP address) field to figure out which net (cable/interface) to send the packet to. [UDP checksum.]

Next: 7.4. Server/Gateway Receives BOOTREPLY

Connected: An Internet Encyclopedia
7.3. Server Receives BOOTREQUEST


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