Avaya Configuring IP, ARP, RIP, and OSPF Services Uživatelský manuál stáhnout pdf (Strana 42)

Configuring IP, ARP, RIP, and OSPF Services

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Route Weights

Route-weight calculation is an internal tool that IP uses to facilitate the selection

of the best route among alternative routes to the same destination. Route-selection

criteria are encoded into the route weight in a way that allows IP to compare

routes simply by comparing their weight values, regardless of route sources.

Appendix D

contains a worksheet that you can use to calculate route weights in

your configuration.

Route-weight calculation increases the efficiency of the route-selection process. It

also reduces the size of the routing database because all route selection parameters

for each route are encoded in a single integer -- the weight value -- rather than

stored in separate variables.

Using selection criteria encoded in the route weight, IP chooses routes in the

following order:

1. The route with the highest preference value (see “Route Preferences” on page

1-19)

2. A direct route with the lowest metric

3. An OSPF intra-area route with the lowest metric

4. An OSPF interarea route with the lowest metric

5. An OSPF type 1 external route with the lowest metric

6. A BGP route with the highest LOCAL_PREF value

7. A RIP route with the lowest metric

8. An EGP route with the lowest metric

9. A static route with the lowest metric

Note:

If OSPF is configured to propagate external routes using the route

weight as the type 2 metric, routes that are received as OSPF ASE type 2

routes are evaluated according to their respective origins (for example, RIP or

BGP).

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Avaya Configuring IP, ARP, RIP, and OSPF Services Uživatelský manuál Strana 42