BGP route selection principle and attribute detailed explanation: weight

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.

Weight attribute Detailed:

Weight only has local significance he cannot be routed by routers only on this route, and he is Cisco's private Property! He is the one who influences himself without affecting the attributes of others!! In Cisco, the weight attribute has the highest priority. In other vendors, start with the Local_pref property.

The BGP weight property is a local property. Weight This property is configured locally on the router and is not propagated to any other routers. If there are multiple routes to the same destination router, then the weighted Highland route will be selected first.

If the originating router generated by the route is set to 32768 by default for the weight property. The weight of other routes defaults to 0.