ThomasineManion114

To pass the BSCI exam and earn your CCNP, you've got to know ISIS inside and out. There are several similarities amongst ISIS and OSPF, but 1 significant distinction is that ISIS has three various sorts of routers - Level 1 (L1), Level 2 (L2), and L1/L2. enagic L1 routers are contained in a single region, and are linked to other areas by an L1/L2 router. The L1 makes use of the L1/L2 router as a default gateway to reach destinations contained in other locations, significantly like an OSPF stub router uses 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 very same location need to synchronize their databases with every single other. Just as we have L1 routers, we also have L2 routers. Anytime we're routing amongst regions (inter-area routing), an L2 or L1/L2 router need to be involved. All L2 routers will have synchronized databases as nicely. Each L1 and L2 routers send out their personal hellos. As with OSPF, hello packets let ISIS routers to type adjacencies. The crucial distinction 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 identical link, they will not form an adjacency. enagic 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 regions. The L1/L2 router will have two separate databases, though - one for L1 routes and one more for L2 routes. L1/L2 is the default setting for Cisco routers operating ISIS. The L1/L2 router is the router that makes it attainable for an L1 router to send information to yet another place. In the subsequent component of my ISIS tutorial, we'll take a far more comprehensive look at these ISIS hellos!