Considerations for Router Setup cost

OSPF routing protocol is a typical link state routing protocol, which is generally used in the same routing domain, where the routing domain refers to an autonomous system, i.e. as, which is a set of networks that Exchange routing information with each other through a unified routing policy or routing protocol.

In this as, all OSPF routers maintain an identical database that describes the as structure, which holds the status information of the corresponding link in the routing domain, which is the way the OSPF router computes its OSPF routing table.

First, we configure the interface of the IP and OSPF protocol, routers configured to Frame Relay switch, so more conducive to our better understanding of Frame Relay, note: In the interface of the router, you can define the interface type IP OSPF network broadcast or a neighbor who can manually specify two interfaces , or they will not be neighbors.

Second, then we can go into the interface of each route to manually specify the cost value, the command is in the interface: IP OSPF cost Note: The default value of the Ethernet port is 1. WAN Port defaults to 64,OSPF default value of 100 divided by the interface bandwidth 1.544=64 can go to show interface query, router source interface to other networks, is to take the cost value of the interface as the path orientation. For example: R3 s1/0 and S1/1 if s1/0 does not manually specify the cost value. The default is 64. Then R3 to the other route does not take s1/0 this interface.

Third, through the common sense analysis router's cost is smallest, should take 2 this road to go, but the fact is not, found that after walking R2 directly to R1, and do not go according to 172.16.255.0 network section this side cost value is 10. And go R4, this path is SPF calculated.

When R3 the packet to R2, R2 found that the packet was to reach other networks.

Therefore, R2 does not transfer packets to other routers in the same area. Since R2 is an ABR, he believes that the data packets arriving in other areas need to be forwarded directly to the backbone area. And I also happen to be connected with the backbone area. Therefore, R2 directly forwards packets to the R1 router in the backbone area.

It is for this reason that the route we are looking at is inconsistent with the path that actually forwards the packet.

Five, let's take a look at R3-R2-R4, the original cost is: 4, because I defined the R2 f0/0 cost is 2, note: This section of the cost is not 1, because Ethernet it will be out of the interface to calculate, not to select the minimum value of the network segment to carry out the stack of the path, R3-R4, We change the f0/0 cost of R2 to 3. This is two is 5, after the change.

We show the IP route look, found that the 192.168.1.0 this section of the two path of the load balance.

As a link state routing protocol, OSPF transmits the link state broadcast data LSA to all routers in a zone, unlike the distance vector routing protocol, where the router running the distance vector routing protocol passes some or all of the routing tables to its neighboring routers.