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To pass the BSCI exam and earn your CCNP, you have got to know ISIS inside and out. There are several similarities between ISIS and OSPF, but one significant difference is that ISIS has 3 different sorts of routers - Level 1 (L1), Level 2 (L2), and L1/L2.

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

L1 routers have no certain routing table entries regarding any destination outside their own region they will use an L1/L2 router as a default gateway to reach any external networks. ISIS L1 routers in the 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 between areas (inter-place routing), an L2 or L1/L2 router need to be involved. All L2 routers will have synchronized databases as well.

Both L1 and L2 routers send out their personal hellos. As with OSPF, hello packets let ISIS routers to type adjacencies. The key 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 same link, they will not form an adjacency.

An ISIS router can act as an L1 and an L2 router at the 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 an additional for L2 routes. L1/L2 is the default setting for Cisco routers running ISIS. The L1/L2 router is the router that makes it attainable for an L1 router to send data to yet another location.

In the subsequent portion of my ISIS tutorial, we'll take a a lot more detailed look at those ISIS hellos! internet baking soda alkaline water internet baking soda alkaline water look into alkaline diet