DFS

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 form adjacencies.  The key difference 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 – one for L1 routes and another for L2 routes.  L1/L2 is the default setting for Cisco routers running ISIS.  The L1/L2 router is the router that makes it possible for an L1 router to send data to another area.

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In studying for your CCNA exam and preparing to earn this valuable certification, you may be tempted to spend little time studying static routing and head right for the more exciting dynamic routing protocols like RIP, EIGRP, and OSPF. This is an understandable mistake, but still a mistake. Static routing is not complicated, but it’s an important topic on the CCNA exam and a valuable skill for real-world networking.

To create static routes on a Cisco router, you use the ip route command followed by the destination network, network mask, and either the next-hop IP address or the local exit interface. It’s vital to keep that last part in mind – you’re either configuring the IP address of the downstream router, or the interface on the local router that will serve as the exit interface.

Let’s say your local router has a serial0 interface with an IP address of 200.1.1.1/30, and the downstream router that will be the next hop will receive packets on its serial1 interface with an IP address of 200.1.1.2/30. The static route will be for packets destined for the 172.10.1.0 network. Either of the following ip route statements would be correct. R1(config)#ip route 172.10.1.0 255.255.255.0 200.1.1.2 (next-hop IP address)

OR

R1(config)#ip route 172.10.1.0 255.255.255.0 serial0 ( local exit interface)

You can also write a static route that matches only one destination. This is a host route, and has 255.255.255.255 for a mask. If the above static routes should only be used to send packets to 172.10.1.1., the following commands would do the job.

R1(config)#ip route 172.10.1.1 255.255.255.255 200.1.1.2 (next-hop IP address)

OR

R1(config)#ip route 172.10.1.1 255.255.255.255 serial0 ( local exit interface)

Finally, a default static route serves as a gateway of last resort. If there are no matches for a destination in the routing table, the default route will be used. Default routes use all zeroes for both the destination and mask, and again a next-hop IP address or local exit interface can be used.

R1(config)#ip route 0.0.0.0 0.0.0.0 200.1.1.2 (next-hop IP address)

OR

R1(config)#ip route 0.0.0.0 0.0.0.0 serial0 ( local exit interface)

IP route statements seem simple enough, but the details regarding the next-hop IP address, the local exit interface, default static routes, and the syntax of the command are vital for success on CCNA exam day and in the real world.

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If you are a beginner in learning about Cisco Router, remember that working on the router is not really difficult. Like anything else in life, you need to learn how to use work it. Learn how to use the commands is the essential things you need to learn about Cisco router. I suggest for learning purpose to check this Tomax 7 website for commands. Other site that might help PK Networking.

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