When a router is going to forward a packet, it must determine whether
it can send it directly to its destination, or whether it needs to
pass it through another router. If the latter, it needs to determine
which router to use. This section explains how these determinations
are made.
This section makes use of the following definitions:
LSRR - IP Loose Source and Record Route option
SSRR - IP Strict Source and Record Route option
Source Route Option - an LSRR or an SSRR
Ultimate Destination Address - where the packet is being sent to:
the last address in the source route of a source-routed packet, or
the destination address in the IP header of a non-source-routed
packet
Adjacent - reachable without going through any IP routers
Next Hop Address - the IP address of the adjacent host or router to
which the packet should be sent next
IP Destination Address - the ultimate destination address, except
in source routed packets, where it is the next address specified
in the source route
Immediate Destination - the node, System, router, end-system, or
whatever that is addressed by the IP Destination Address.