Link-state packets

General:

The second category of IS-IS packets are the link-state packets (LSPs). Opposing to hello packets, which are mainly used for subnetwork-dependent functions, LSPs are related with the operation of the subnetwork-independent functions. LSPs are generated by IS-IS routers to describe their immediate surrounding. LSPs contain area information, adjacent routers, IP subnets, metric information and authentication information. These are important parameters which are used for routing. Each LSP contains information which represents a partial view of the whole topology of the area. Within an area routers distribute LSPs. This process is called flooding. Each router within an area takes the link-state information of a packet and stores it in the local link-state database. Every area has its own, unique level-1 (L1) link-state database. Backbone routers can handle level 1 and level 2 (L1L2) routing and have a level 2 (L2) link-state database. This is also a unique link-state database but within a domain.

The structure of a link-state packet:

As aforementioned we distinguish between level 1 and level 2 link-state packets. But the structure is absolutely similar. They only differ in the level 1 or level 2 information they carry. In the structure of a link-state packet the first eight header fields in IS-IS are always the same. The other header fields are:

pdu_link_state_packet.jpg

Table 7: link-state packet format


Meaning of the link-state packet fields

pdu_link_state_packet_description.jpg

Table 8: Description of the link-state packet fields


Sources:

Abe Martey, IS-IS Network Design Solution, Kap. 3

CCNP 1 Ver. 3.1 Kap.8

 
link-state_pakete.txt · Last modified: 2009/09/13 14:37 (external edit)
 
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