BGP attribute Detailed: Local_pref

In the IGP era, we all know, for example, OSPF, link state protocol, in the routing of the time, than the cost of the link, which link consumption will be more priority, if two of the same link consumption, then do load balancing.

In fact, the 2 principles to achieve the OSPF---shortest path first work principle.

What if, in BGP, there are multiple routes to achieve the goal, how should the choice be made? Which path is the preferred one?

Take a look at the priority of these 11 attributes, and deepen the memory, preferably with a skilled back:

1 Highest Weight--cisco private properties

2 Highest Local Prerence-----recognized well-known mandatory

3 ROUTE originated by the ROUTER NEXT hop=0.0.0.0 *-----Recognized must be respected well-known mandatory

4 Shortest as PATH *-----recognized well-known mandatory

5 LOWEST originated igp> Egp>incomplete *-----Recognized well-known mandatory

6 LOWEST MED

7 EBGP path over IBGP path

8 prefer the PATH throgh the closest IGP neighbor

9 Rrefer oldest ROUTER for EBGP PATH

Prefer the PATH with the LOWEST neighbor BGP ROUTER ID

One BGP LOWEST ROUTER ID

MINIMUM Claster LIST LENGTH

In BGP, in addition to a large set of principles to be understood, the principle of route selection is the most important. Must be mastered (to understand and troubleshoot BGP, here must be to grasp rather than understand) the route principle.

Each property is validated by the document one at a time. To be able to reach myself in the mind of these concepts.

Local_pref attribute Detailed:

Local_pref is used to advertise the priority of a route, only to be exchanged between IBGP peers and not to other as. That is, it only takes effect within this as. When a BGP router obtains the same address as the destination through a different IBGP counterpart but the next hop on a different number of routes ( In other words, different IBGP neighbors notice the same destination routing, there is multi-hop case, in Cisco in addition to the weight attribute, is the Local_pref attribute the highest priority. Local_pref property values are the same as weight, the higher the precedence.

From the application of the online to see the difference between weight and local_pref:

Local_pref and weight are also different, weight use is a ASBR to connect two different as ASBR respectively. Local routers as the only export, when there are multiple paths in the local set priority weight weight, the weight of a large priority. Weight is only valid on the local router.

and Local_pref only when a IBGP router obtains a route with the same destination segment from another two IBGP neighbors, if weight is not set (the default is 32768 for the initial router and 0 for any other router), Then this time to see the two routes sent over the local_pref of the attribute value, which is large, then which route priority, thus writing to the routing table as the best route, there is a suboptimal route in the database, and other main use of the problem, the suboptimal route effective.

Local_pref Summary:

Only for IBGP neighbors, just as inside.

Default 100. The optional range is: 0-4294967295.

Show ip BGP. can see LOCPRF.

Announcements are made only between IBGP peer. Tell how to leave the local as. is to go a to leave good, or go b leave?

The higher the value, the higher the priority. BGP is not based on bandwidth, but on strategy.

This is an outbound policy.