Cisco CCNP / BSCI Exam Tutorial: ISIS Router Types
To pass the BSCI exam and earn your CCNP, you’ve got to know ISIS inside and out. There are many similarities between ISIS and OSPF, but one major difference is that ISIS has three different types of routers – Level 1 (L1), Level 2 (L2), and L1/L2.
L1 routers are contained in a single area, and are connected to other areas 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 uses the ABR as a default gateway.
L1 routers have no specific routing table entries regarding any destination outside their own area; they will use an L1/L2 router as a default gateway to reach any external networks. ISIS L1 routers in the same area must synchronize their databases with each other.
Just as we have L1 routers, we also have L2 routers. Anytime we’re routing between areas (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 allow ISIS routers to...
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