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To pass the BSCI exam and earn your CCNP, you've got to know ISIS inside and out. There are numerous similarities among ISIS and OSPF, but one main distinction is that ISIS has three various types of routers - Level 1 (L1), Level 2 (L2), and L1/L2.

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

L1 routers have no particular routing table entries relating to any destination outside their own place they will use an L1/L2 router as a default gateway to reach any external networks. ISIS L1 routers in the exact same area ought to synchronize their databases with every single other.

Just as we have L1 routers, we also have L2 routers. Anytime we're routing amongst areas (inter-location routing), an L2 or L1/L2 router must be involved. All L2 routers will have synchronized databases as well.

Both L1 and L2 routers send out their own hellos. As with OSPF, hello packets allow ISIS routers to form adjacencies. The essential distinction right 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 very same link, they will not type an adjacency.

An ISIS router can act as an L1 and an L2 router at the identical time these routers are L1/L2 routers. An L1/L2 router can have neighbors in separate ISIS locations. The L1/L2 router will have two separate databases, although - 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 feasible for an L1 router to send information to an additional area.

In the subsequent component of my ISIS tutorial, we'll take a much more detailed look at these ISIS hellos! web address h2go article official link