Bootstrap Protocol (BOOTP) is based on IP / UDP protocol of the agreement, which allows a diskless station from a central server to obtain IP addresses for the diskless workstation LAN IP address assigned dynamically, does not require each user to set a static IP address. When using the BOOTP protocol, generally include Bootstrap Protocol Server (bootstrap protocol server) and the Bootstrap Protocol Client (Bootstrap Protocol Client) in two parts.
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RARP control and semantic meaning of the Chinese interpretation of the English original application of a general description of the main points of RFC Detailed protocol: packet format chicken and egg problem if the client knows its own IP address if the client has do not know your IP address using ARP packet processing at the client 1, client to send 2, 3 client retransmission strategy, the server receives BOOTREQUEST (boot request) 4, the server / gateway receives BOOTREPLY (boot reply) 5, the client RARP receiving guidance and control through the gateway in English the original meaning of the semantic interpretation of Bootstrap Protocol Bootstrap Protocol Chinese general description of the application of the protocol is mainly used in a diskless workstation LAN, get IP address of the client as follows: First, the boot code from the BOOTP start the client, this time the client has no IP address, use the IP address 255.255.255.255 broadcasts to send to the network IP address lookup request. Then, run the BOOTP protocol server receives this request, will be provided upon request to find the client MAC address, IP address and sends a contains the server IP address, gateway and other information of the FOUND frame. Finally, the client will be according to the FOUND frame to start a dedicated TFTP server to download image files, simulate disk. Detailed description of the RFC RFC a IP / UDP bootstrap protocol (BOOTP), allows a diskless client find their IP address, server host address, and name into a specified file into memory and run. Guide the operation of two stages. This RFC describes the first phase: 'assigned address and select the boot file'. Address and file name in access to information, to entering the second stage boot: file transfer. General use TFTP file transfer protocol [9], because the two phases resides in the client's PROM. However BOOTP can with other protocols such as SFTP or FTP to work together. We recommend that the client's PROM software without user interaction to provide a complete guide way. This is an unattended power-up mode. Must provide a mechanism to allow users to manually provide the address and file name information directly into the bypass BOOTP protocol file transfer stage. If you provide non-volatile storage, where we propose to save the settings to bypass the BOOTP protocol settings cause the file until the transfer phase to fail. If the cached information fails, boot back to the first stage and use BOOTP. The main points of agreement: 1. Using a single packet exchange (information). Use time-out mechanism until you receive the response. Two-way package field with the same structure. Use (the maximum possible length) fixed length fields to simplify structure definition and analysis. 2. An 'opcode' field contains two values. Client broadcasts a 'boot request (bootrequest)' package. Server response a 'boot response (bootreply)' package. 'Bootrequest' contains the client's hardware address, if known, also contains its IP address. 3. Request may contain the client's response to the specified server name. The client can force the boot from a specified host. (If there is a variety of the same boot file version or a remote server in the network / domain.) Clients do not have to deal with name / domain services, this feature pushed to the BOOTP server. 4. Request may contain 'common (generic)' boot file name. For example 'unix' or 'ethertip'. However, the server sends the boot reply, it uses the exact boot file corresponding to the path name to replace the field. Server queries the client's address and the related database file name request to use a custom client-specific boot files to determine the file name. If the boot request file name is the empty string, the server returns a client load with the default file name field. 5. The client does not know their IP address, the server must have a hardware address and IP address of the corresponding database. The client IP address is placed in the boot response (corresponding) field. 6. Some of the network topology (such as Stanford's network) may not have a line in a physical access to the TFTP server directly (for example, some Internet gateway and the host of all is likely to be diskless). BOOTP allows a client to the gateway by using the adjacent jumps from several servers outside the boot. Consider the following 'guide through the gateway' section. This part of the agreement does not require the client to do a specific part of the action. Implementation is optional, gateway and server needs some additional code. Packet format unless otherwise noted, all figures are shown in decimal. For simplicity, assume that BOOTP packets are not fragmented. All figures in the field using the standard network byte order. That is, the first to send high bits. IP header in the boot request, the client to fill out if you know their IP source address, or fill in 0. When the server does not know when the address, IP destination address is broadcast address 255.255.255.255. This address means 'broadcast on the local line, I do not know my network number' [4]. UDP header contains source and destination port number. BOOTP protocol uses two reserved port numbers, 'BOOTP client' (68) and 'BOOTP server' (67). Customers 'BOOTP server' as the destination port to send the request; This is usually the broadcast. Server using 'BOOTP client' as the destination port to send response; depends on the server core or drives, which may or may not be broadcast (in the following 'chicken and egg problem' in-depth explanation of the title of the chapter). Uses two reserved port due to be broadcast the boot reply to the client to avoid the 'wake up' and scheduling BOOTP server process. Because the server and other hosts will not listen 'BOOTP client' port, all incoming broadcast packets will be filtered out in the core level. We can not simply allow the client to find a random UDP source port as the port number field; because the server response may be broadcast, a randomly chosen port number could confuse other happens to be listening on that port of the host. UDP length field set to UDP plus BOOTP part of the package length. UDP checksum to the client (or server) in accordance with the need to set to 0 to avoid additional costs PROM implementation. In the following 'package deal' section '[UDP checksum]' phrase may be used to indicate the checksum verification / calculation. The number of bytes field description ----- ----- ----------- op 1 packet op code / message type. Packet opcode / message type 1 = BOOTREQUEST (boot request), 2 = BOOTREPLY (boot reply) htype 1 hardware address type, hardware address type see ARP section in 1 hardware address length of hardware address length (eg '6 'for 10mb ethernet). for example, '6' is a 10M Ethernet hops 1 client sets to zero, the client is set to 0 optionally used by gateways in the gateway boot across the gateway choose to use in cross-gateway booting. xid 4 transaction ID, a random number, used to match this boot request with the responses it generates. transaction ID, a random number used to match the reference request and response secs 2 filled in by client , seconds elapsed since client started trying to boot. completed by the client, the client guide the number of seconds after the start of the last - 2 unused unused ciaddr 4 client IP address; client IP address,
nike air force one high, filled in by client in bootrequest if known . If the client knows the request to fill in the boot yiaddr 4 'your' (client) IP address; 'your' (client) IP address filled by server if client doesn't know its own address (ciaddr was 0) . If the client does not know its address (ciaddr 0), the server fill siaddr 4 server IP address; server IP address returned in bootreply by server. response returned by the server at boot giaddr 4 gateway IP address, gateway IP address used in optional cross-gateway booting. boot across the gateway can choose to use chaddr 16 client hardware address, client hardware address filled in by client. by the client fill out sname 64 optional server host name, an optional server host name null terminated string. null terminated string file 128 boot file name, null terminated string; boot file name, null terminated string 'generic' name or null in bootrequest, in the boot request to use the 'generic' name or the fully qualified directory-empty path is to guide the response in the name of the directory path to use the exact name in bootreply. vend 64 optional vendor-specific area, the optional vendor specific area, eg could be hardware type / serial on request, for example, can be requested hardware type / serial , or 'capability' / remote file system handle or the response of the performance / remote file system handle. on reply. This info may be set aside for use of this information to guide left to third parties or core (program) to use. by a third phase bootstrap or kernel. chicken and egg problem if the client does not know their own IP address, the server how to send IP packets to the client. Whenever a lead response is sent, the sending device do the following: If the client knows its own IP address ('ciaddr' field non-zero), because the client can respond to ARPs [5], then the IP can be properly sent. If the client does not know your IP address (ciaddr is zero), the client can not send a response to guide the response process back ARPs. Then there are two options: a. If the sending program has the necessary core or driver hooks to manually create ARP address cache entry, you can use 'chaddr' and 'yiaddr' fill in an entry field. Of course, this ARP entry, as normal as other items created a life time,
air force one low nike, to guide the response to be able to simply send the program guide the response sent to the client's IP address. UNIX (4.2 BSD) has this capability. b. If the sending program is missing the core hooks to send only a simple interface to guide the appropriate response to the broadcast address. This is just in front of circumstances additional broadcasts. ARP client using the client PROM must contain a simple implementation of ARP, for example, address buffer can hold an entry. This allows the client to know the IP address and boot file name after the implementation of the second phase of the boot (TFTP). Any time the client should be prepared to respond to its own IP to hardware address mapping of the ARP request (if known) to receive a TFTP or BOOTP response. Because the answer will contain the boot server / gateway hardware source address (in hardware package), the client can avoid sending an ARP request to apply for subsequent stages of use TFTP server / gateway IP address. But this should only be a special case, as described above, only the second phase of the boot is still allowed. RARP Duizhao with an earlier proposal to use the client protocol,
air force 1 shoes, Reverse Address Resolution Protocol (RARP) [1] to determine the hardware address through its own IP address. However RARP disadvantage is that it is a hardware link layer protocol (not based on IP / UDP). This means that RARP could only contain a special message for the access to the original core and the drive to modify the host implementation. Because there are now many different organizations to maintain the network core, the core of a guide does not require modification agreement is a definite advantage. BOOTP useful addition to the above sections describe the features, but also provide the hardware to the IP address of the query. 1 packet processing, the client established the first packet sent before, it is best to clear the entire packet buffer; This will set all the default fields. Any client to establish the following fields in the package. IP destination address is set to 255.255.255.255 (broadcast address) or the server's IP address (if known). IP source address and 'ciaddr' set the client IP address (if known), or 0. Use the appropriate length of the UDP header set; source port = 'BOOTP client' port destination port = 'BOOTP server' port. 'Op' is set to '1 ', BOOTREQUEST (boot request). 'Htype' set in the 'Hlen' is set to the length of hardware address, for example, 10M Ethernet is '6 '. 'Xid' is set to a 'random' transaction ID. 'Secs' is set to boot the client over the past number of seconds after the start. This let the server know the client has tried more than a long time. When the numbers become larger, some servers may be more attention to the client to provide different services. If the client is the lack of a suitable clock, it can use the cycle timer to establish a rough estimate of value. Or it may choose to simply send a fixed value of the field, such as 100 seconds. If the client know the IP address, 'ciaddr' (and the IP source address) set to this value. 'Chaddr' completed using the client hardware address. If the client wishes to restrict a specific server name from the boot to be in the 'sname' in the end put an empty string. Using the corresponding host name should be the proper name or alias. The client in completing the 'file' file name field for a number of options. If set to null, which means 'I use the default file to boot my machine'. An empty file name also means 'I am only to find client / server / gateway IP address of interest, I do not care about the file name'. This field can also be a 'generic' name into the 'unix' or 'gateway'; which means 'to use the naming process configuration to boot my machine'. Finally, this field may be the exact directory path name. 'Vend' field can be filled by the client vendor string or structure. For example, you can fill out the machine hardware type or serial number. However, the operation of BOOTP server should not rely on these existing information. If you are using the 'vend', recommended for 'vend' the first project is a 4 byte 'magic word (magicnumber)'. This allows the server to determine it in this field to see what type of information. Values can be normally the 'magic word' process allocation, you pick one, it becomes magic word. And guidance to guide the response is a magic word request to allow different client response information in accordance with the special action. [UDP checksum] 2, the client retransmission strategy in a long period of time does not receive response, the client should retransmit the request. Time interval must be carefully selected not to cause network storms. Consider a network containing 100 machines after a power failure situation. Every four seconds a simple retransmission request will flood the network. One possible strategy, you might consider the exponential compensation, such as Ethernet, as in the collision. For example, the first packet in 0:00, the second at: 04, then: 08, then: 16,: 32,: 64. You should be randomized each time; It is like a mask as the Ethernet specification 'and' a random number to enter for the first time compensation. In each subsequent compensation, the mask up a bit. This average delay in each double compensation. In the 'average' Compensation arrived 60 seconds, you no longer growing, but still randomized. Before each retransmission, the client should be revised 'secs' field. [UDP checksum] 3, the server receives BOOTREQUEST (boot request) [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 alias, to continue the package deal. If the sname field is specified, but does not match 'us', then there are several options: 1. You can choose to simply discard the packet. 2. If the query sname the name of the display it on a network, discard the packet. 3. If the sname in a different network,
nike air force one, you can choose to forward the packet to that address. If so, check 'giaddr' (gateway address) field. If the 'giaddr' is 0, fill in my address or can be used to reach the network gateway address. Then forwards the packet. If the client IP address (ciaddr) is 0, then the client does not know their IP address. Try to find in our database client hardware address (chaddr, hlen, htype). If no match, discard the packet. Otherwise, the client that we now have an IP address; fill 'yiaddr' (your IP address) field. We now check the boot file name field (file). If the client does not care about the default file name or you want to boot file, this field is empty. If the field is not empty, it can be the IP address and the client as the database query keywords. If the default file or generic file (possibly by the client address as the index) or a name that matches the specified path, and then 'file' field, enter the selected boot file specified path name. If the field is non-empty and there is no match, then we do not want a client file, discard the packet, and perhaps other BOOTP server has the file. Vendor specific data field 'vend' should now be examined. If you provide a recognizable type of data, the client should be specified in the action, and to fill in the reply packet in response to the 'vend' data field. For example, a workstation client could provide a verification word, and from the server receives a remote file access permissions, or set of boot configuration options will soon pass into the operating system. My (server) IP address to the box 'siaddr' field. Set 'op' field BOOTREPLY (boot reply). UDP destination port set to 'BOOTP client'. If the client address 'ciaddr' non-0, the packet there; Otherwise, if the gateway address 'giaddr' non-0, set the UDP destination port to 'BOOTP server' and the packet sent to the 'giaddr'. Otherwise, the client in one of our network, but it does not know your IP address, use the above 'egg' method described in the chapter to send it to the client. If you use the 'egg' and we have many interfaces on the host, use the 'yiaddr' (your IP address) field indicates which network to send packets to the (network / interfaces.) [UDP checksum] 4,
nike air force one low, the server / gateway receives BOOTREPLY (boot reply) [UDP checksum] If 'yiaddr' (your [client's] IP address) points to one of our network, use the 'Egg' methods to forward it to the client. Sure to send it to the 'BOOTP client' UDP destination port. 5, do not forget the client receives the IP address for my own (if I know) deal with ARP requests. [UDP checksum] the client should be dropped into the package the following: It is not targeted to guide the port's IP / UDP; not BOOTREPLY (boot reply); does not match my IP address (if I know) or my hardware address; not match my business ID. Otherwise, we received a successful response. If I did not know the words, 'yiaddr' contain my IP address. 'File' is the TFTP 'read request' in the file name. Server address in the 'siaddr' in. If the 'giaddr' (gateway address) non-0, then the packet should be forwarded to there, and then to the server. Guide this part of the agreement through the gateway is optional and requires a lot of gateways and servers with the extra code, but it allows the boot across the gateway. This is mainly useful when gateways are diskless machines. Reel gateway (for example, a UNIX machine as a gateway) may run their own BOOTP / TFTP server. Listening BOOTREQUEST (boot request) may be determined by the gateway to forward broadcast or rebroadcast these requests properly. For example, as part of the table configuration, the gateway can have a receiver any BOOTREQUEST (boot request) broadcast a list of other networks or hosts. Even consider a 'hops' field, the simple request of all the re-broadcast is still a poor method, because broadcast cycle will almost certainly occur. Forwarding can begin immediately, or wait 'secs' (seconds client attempts) field exceeds a certain threshold. Forwards the request to determine if a gateway, it should see 'giaddr' (gateway IP address) field. If it is 0, it in the field add their own IP address (in the receiving network.) Can also use the 'hops' field to optionally control how far can forward packets. Should increase the number of hops per transponder. For example, if you jump more than '3 ', the package should be discarded. [UDP checksum] Here we recommend an increase in the gateway to forward this particular function. But not always like that. There are some online 'BOOTP forwarding agent' to guide the client, these agents can be properly forwarded. So that these services can and gateway together, can not together. When the forwarding agent does not and gateway together,
air force one high, the agent can be guided by the request received 'giaddr' field is the broadcast address with the interface to save some work. This response can use the gateway to forward common and does not include forwarding agent. Disadvantage is that you lose of course, use the 'Egg' non-broadcast mode to send the response capacity, resulting in the client host for each additional line costs. More Atlas Atlas entry Open Category: Network, network protocols to improve my
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