IGP calculates the interface cost automatically
Created: Oct 31, 2019 09:34:22Latest reply: Oct 31, 2019 09:47:39
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Hello,
IGP protocols include RIP, IS-IS, and OSPF. Calculating the Cost of a RIP Route RIP measures the distance from the local end to the destination by hop count. The hop count is also called the metric. RIP defines that the hop count from a router to a directly connected network is 0, and the hop count from a router to a network that can be reached through another router is 1. The hop count increases with the number of routers between the local router and the destination network. To limit the convergence time, RIP defines that the hop count must be an integer ranging from 0 to 15. A hop count of 16 or greater is defined as infinite. That is, the destination network or host is unreachable. An interface does not add the cost to RIP routes to be sent, but increases the cost by 1 for the received RIP routes. You can run the following commands to change the cost of routes:
You can run one of the following commands to set the metric of the imported routes. The following commands are listed in descending order of priority:
On an IS-IS network, the default cost of an IS-IS interface is 10. The cost of an IS-IS route is the sum of costs of all links between the source device and the destination device. The link cost of an IS-IS interface can be calculated in the following modes in descending order of priority:
Table 1 Relationship between the IS-IS interface cost and interface bandwidth  NOTE: A Level-1 router in the Level-1 area must communicate with a router outside the Level-1 area through the default route generated on the Level-1-2 router. Therefore, the cost of the route from the Level-1 router to the router outside the Level-1 area is the cost of the route from the Level-1 router to the closest Level-1-2 router. IS-IS can be configured to specify the cost for the imported route or retain the original cost of the imported route. Calculating the Cost of the OSPF Route Similar to the cost of an IS-IS route, the cost of an OSPF route is the sum of costs of all links along the route. By default, the link cost of an OSPF interface is 1. You can run the ospf cost command to set the cost for a specified OSPF interface. If no interface cost is configured, the system calculates the interface cost using the following formula:
NOTE: Packets between the stub router or total stub router and a router outside the AS are forwarded through the default route generated on the ABR. Therefore, the cost of the route from the stub router or total stub router to the router outside the AS is the cost of the route from the outside the stub router or total stub router to the closest ABR. Similarly, the cost of the route from the NSSA router to a router in another area or AS is the cost of the route from the NSSA router to the closest ABR or ASBR. Thanks |
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