Cisco CCNP / BSCI Exam Tutorial: ISIS Router Types
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 particular key distinction is that ISIS has three different sorts of routers – Level 1 (L1), Level two (L2), and L1/L2.
L1 routers are contained in a single region, and are linked to other locations by an L1/L2 router. The L1 makes use of the L1/L2 router as a default gateway to reach destinations contained in other places, much like an OSPF stub router utilizes the ABR as a default gateway.
L1 routers have no particular routing table entries relating to any destination outdoors their personal region they will use an L1/L2 router as a default gateway to reach any external networks. ISIS L1 routers in the identical place should synchronize their databases with each and every other.
Just as we have L1 routers, we also have L2 routers. Anytime we’re routing among locations (inter-area 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 let ISIS routers to type adjacencies. The crucial 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 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 – a single 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 possible for an L1 router to send data to an additional area.
In the next component of my ISIS tutorial, we’ll take an a lot more comprehensive look at those ISIS hellos!
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