IS-IS Packets
As discussed earlier, link-state protocols maintain information received from neighbors. Any information received from a neighbor is maintained in a database. Because link-state protocols require the information to be constant among neighbors, IS-IS has different protocol packets. Essentially, IS-IS has four packet types:
Hello packets
LSPs
CSNP data units
PSNP data units
Each of these is discussed in more detail in the following sections.
Hello Packets
Hello packets are sent to multicast MAC-layer addresses to determine whether other systems are running IS-IS. There are three types of hello packets in IS-IS: one for point-to-point interfaces, one for level 1 routers, and one for level 2 routers. The hellos sent to level 1 and ...
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