CowleyStrain983

To pass the BSCI exam and earn your CCNP, you have got to know ISIS inside and out. There are a lot of similarities between ISIS and OSPF, but one particular main difference is that ISIS has three distinct varieties of routers - Level 1 (L1), Level two (L2), and L1/L2. L1 routers are contained in a single area, and are linked to other regions by an L1/L2 router. The L1 uses the L1/L2 router as a default gateway to reach destinations contained in other places, significantly like an OSPF stub router makes use of the ABR as a default gateway. L1 routers have no specific routing table entries regarding 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 identical area ought to synchronize their databases with each and every other. division Just as we have L1 routers, we also have L2 routers. Anytime we're routing in between places (inter-region routing), an L2 or L1/L2 router ought to be involved. All L2 routers will have synchronized databases as well. tumbshots Each L1 and L2 routers send out their personal hellos. As with OSPF, hello packets enable ISIS routers to type adjacencies. The essential difference 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 form 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 places. The L1/L2 router will have two separate databases, even though - 1 for L1 routes and yet another for L2 routes. L1/L2 is the default setting for Cisco routers operating ISIS. The L1/L2 router is the router that makes it feasible for an L1 router to send information to another place. In the subsequent part of my ISIS tutorial, we'll take a far more detailed look at these ISIS hellos!