YetterMraz119

To pass the BSCI exam and earn your CCNP, you have got to know ISIS inside and out. There are many similarities amongst ISIS and OSPF, but 1 key distinction is that ISIS has three distinct varieties of routers - Level 1 (L1), Level 2 (L2), and L1/L2.

L1 routers are contained in a single region, and are connected to other places by an L1/L2 router. The L1 makes use of the L1/L2 router as a default gateway to reach destinations contained in other regions, significantly like an OSPF stub router utilizes the ABR as a default gateway.

L1 routers have no precise routing table entries regarding any destination outdoors their personal area they will use an L1/L2 router as a default gateway to reach any external networks. ISIS L1 routers in the very same region ought to synchronize their databases with each and every other.

Just as we have L1 routers, we also have L2 routers. Anytime we're routing amongst places (inter-region routing), an L2 or L1/L2 router should be involved. All L2 routers will have synchronized databases as properly.

Both L1 and L2 routers send out their own hellos. As with OSPF, hello packets allow ISIS routers to type adjacencies. The important difference here is that L1 routers send out L1 hellos, and L2 routers send out L2 hellos. If you have an L1 router and an L2 router on the exact same link, they will not form an adjacency.

An ISIS router can act as an L1 and an L2 router at the exact same time these routers are L1/L2 routers. An L1/L2 router can have neighbors in separate ISIS areas. The L1/L2 router will have two separate databases, though - 1 for L1 routes and one more for L2 routes. L1/L2 is the default setting for Cisco routers running ISIS. The L1/L2 router is the router that tends to make it attainable for an L1 router to send information to one more place.

In the next element of my ISIS tutorial, we'll take a much more detailed look at those ISIS hellos! per your request tumbshots nitrate pre-filter