The detailed meaning of each field will be explained

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Unformatted text preview: ld will be explained in the following slides. 9 BootP - Message Fields Operation Code (OP) Message Type Hardware Address Type (HTYPE) Hardware Address Length (HLEN) Hops Broadcast loop/storm avoidance Increased/checked by routers (C) Herbert Haas 2005/03/11 10 The Hops field is important to avoid broadcast loops in a network. Every time a BOOTP packet is checked by a router, the router increase the hops field per 1. Operation Code (OP) 1… Boot request 2… Boot reply Hardware Address Type (HTYPE) Network Type (1… Ethernet 10MBit) Hardware Address Length (HLEN) 6… Ethernet 10 BootP - Message Fields Transaction ID Used for identification (random number) Seconds Seconds elapsed since client started trying to boot Client IP-address Filled in by client in boot request if known Your IP-address Filled by server if client doesn't know its own address (C) Herbert Haas 2005/03/11 11 The Transaction ID consists of a random number and ensures that a client identifies the correct reply packet among others, associated to its request. That is, both the request and the assoicuated reply have the same Transaction ID. Seconds is set to the number of seconds that have elapsed since the client has started booting. According to RFC 951: "This will let the servers know how long a client has been trying. As the number gets larger, certain servers may feel more 'sympathetic' towards a client they don't normally service. If a client lacks a suitable clock, it could construct a rough estimate using a loop timer. Or it could choose to simply send this field as always a fixed value, say 100 seconds." If a router is configured to forward BOOTP requests (broadcasts) then it might also wait until a certain value for "Seconds" has been exceeded. This measure would mitigate broadcast storms. The Client might fill in its own IP address if already known and other parameters are requested. Mostly "Your IP address" is used, which contains the IP address assigned to the client. 11 Boo...
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This document was uploaded on 02/12/2014.

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