What is the route selection criteria in BGP?

BGP Path Selection Criteria Choose the route with the highest weight. If weight is not set, choose the route with the highest local preference. Choose routes that this router originated. Choose the path with the shortest Autonomous System path.

How does BGP select the best routing path?

If there are no specific settings that can affect the outcome, BGP Best Path Selection Algorithm determines the best route by selecting the shortest path to the destination. An Autonomous System is a single network or a set of networks and routers, which are under the control of one administrative entity.

What is BGP local preference attribute?

Local preference is the second BGP attribute and is used to choose the exit path for an autonomous system. The BGP preference has to be set inbound on routes being received to influence the outbound routing behaviour. A higher local preference is preferred and the default is 100.

What is the most preferred attribute for BGP?

BGP Best Path Selection Algorithm

  • A path with the highest Weight attribute is preferred (other vendors ignore this attribute).
  • A path with the highest “local preference” is preferred (usually set to 100).

How do you prefer a route in BGP?

BGP Table path selection

  1. Prefer the highest local-preference value.
  2. Prefer the shortest AS-path length.
  3. Prefer the lowest origin value.
  4. Prefer the lowest MED value.
  5. Prefer routes learned from an EBGP peer over an IBGP peer.
  6. Prefer best exit from AS.
  7. For EBGP-received routes, prefer the current active route.

What is locally originated in BGP?

Locally Originated: The BGP attribute Locally Originated just as the name implies, prefer the path that the local router originated. A BGP router will prefer routes that it installed into BGP itself, over a route that another router installed in BGP.

What is the difference between local preference and Med?

Unlike with the local preference and weight, where higher is more preferred, with the MULTI_EXIT_DISC, also known as “metric”, the lowest value is preferred. As an “optional non-transitive” attribute, the MED is only present if a router in the local AS or the neighboring AS sets it.

What is the default local preference in BGP?

100
The default value for the local preference is 100. This also means that a route that has no local preference value is treated as if it had a local preference of 100.

Is local preference inbound or outbound?

inbound direction
Local Preference is applied to the inbound direction of the interface. It is the exit point of your AS towards another AS. Different routers have different Local Preference values for that destination and this values is shared within the AS (Autonomous System).

What is the difference between weight and local preference in BGP?

You can use weight instead of local preference to influence the selected path to external BGP peers. The difference is that weight is configured locally and is not exchanged in BGP updates. On the other hand, the local preference attribute is exchanged between iBGP peers and is configured at the gateway router.

How does BGP prevent routing loops?

In BGP there are two loop prevention mechanism:

  1. For EBGP there is AS-Path attribute which states that router will drop BGP advertisement when it sees it own AS number in AS path attribute.
  2. For IBGP there is split horizon rule which states that update sent by one IBGP neighbor should be not send to another IBGP neighbor.

What does next hop 0.0 0.0 mean in BGP?

The next hop of 0.0. 0.0 means that this network originated on this router, that makes sense since I used the network command on R4 to advertise this network into BGP. Further to the right you see metric, local preference and weight. These are the BGP attributes that are used to select the best path.