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IP Datagram Options and Option Format
(Page 3 of 3)
IP Options and Source Routing
Normally, IP datagrams are routed
without any specific instructions from devices regarding the path a
datagram should take from the source to the destination. It's
the job of routers, using routing protocols,
to figure out those details. In some cases, however, it may be advantageous
to have the source of a datagram specify the route a datagram takes
through the network. This is called source routing.
There are two IP options that support
source routing. In each, the option includes a list of IP addresses
specifying the routers that must be used, to reach the destination.
When strict source routing is used, this means that the path
specified in the option must be used exactly, in sequence, with no other
routers permitted to handle the datagram at all. In contrast, loose
source routing specifies a list of IP addresses that must be followed
in sequence, but having intervening hops in between the devices on the
list is allowed.
For full details on the exact structure
used by each option type, please refer to RFC 791.
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The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
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