OSPF computing route

1. OSPF computing route

Although o s p f is complex, it uses one of the following two simple methods to calculate route consumption:
· The default value of Non-bandwidth sensitivity can be used for every o s p f interface.
· OSPF can automatically calculate the consumption of each routing interface.

Regardless of the method used, the consumption of any route can be calculated by adding the consumption of each router interface on the route. In the Shortest Path Tree of o s p f, the sum of consumption of each known destination is recorded.

Ii. Use automatic OSPF computing

O s p f can automatically calculate the consumption of an interface. This algorithm is based on the bandwidth supported by each interface type. The sum (s u m) calculated by all interfaces on a route forms the basis for determining the o s p f route. Based on the bandwidth available on the redundant link, these values allow o s p f to calculate the minimum consumed route. The Network shown in Figure 9 shows this.

Figure 9 route consumption calculated automatically

In Figure 9, network 1 9 3. 1. 3. host and host in network 1 9 3. 1. 4. the Wan routing cost between 0 mid-range systems is 1 3 8. The cost is the cost of two T 1 links between the two networks (each 6 4), and the cost of connecting the Ethernet interface to the network 1 9 3. 1. 4. 0. The cost of Ethernet interfaces between the start and end points is not included in the o s p f cost calculation, because o s p f only consumes the outbound router interfaces. Table 1 summarizes the consumption values automatically calculated by each interface in Figure 9.

 

Iii. Use of default routes in OSPF

Perhaps the reader is most interested in making o s p f automatically calculate the route cost, although this is a bit impossible. For example, the old vro may not support Automatic computing. In this case, all interfaces have the same o s p f cost. Therefore, T 3 will have the same cost as the lease line of 5 6 K B p s. Obviously, these two lines provide different performance levels, which should be the basis for Route decision.
However, some environments accept the cost of using the default route. For example, if a user's network is composed of similar transmission lines, the default value is acceptable. In addition, the administrator can manually modify the consumption measurement for a specific interface. This will enable the network administrator to reasonably plan the network traffic mode while still using the default route.
1. homogeneous network
In homogeneous networks, all transmission lines are the same. For example, all the interfaces of l a n are 1 0 M B p s Ethernet, and all WA N interfaces are T 1. In this case, the use of the default value will not cause Routing Problems. This is correct when there is almost no or few routing redundancy. To display this, consider the network diagram in figure 10.

Figure 10 Use OSPF default Interface values in an acceptable manner

In figure 10, the default value 1 768 is allocated to each interface. However, all the wa n links are T 1. Considering that all values are the same, it does not matter if the allocation value is 1 128, 1 768, or 1 000! The routes in homogeneous networks are determined by simple calculation and comparison of hops. This is correct no matter how many routes are redundant in the network. Obviously, in a network with a lot of redundant routes and different transmission technologies, the default value will not select the optimal route to any destination.
2. manually set the value

In some networks, you want to accept the o s p f default route, and then manually set the special link values different from the default link values. For example, the default consumption value of the user network may be the calculated value of the 1 768-5 6 K B p s serial link.
If only one or two links in the network do not provide the same bandwidth, you can accept the default value and set other values for those special links.
It is not important for o s p f nodes to use automatically calculated route consumption, default consumption, or manual configuration consumption. They accept all such consumption values and calculate the Shortest Path Tree of the network.