Border Gateway Protocol Attributes

BGP Attributes

Fig 1: BGP Attributes

Following are the attributes of the BGP:

1. Weight
2. Local Preference
3. Self Originated
4. AS Path
5. Origin
6. MED
7. Externals
8. IGP Cost
9. EBGP Peering
10. Router ID

Weight

Weight attribute is the BGP attribute which is used when one router is the multihomed and determines best path to leave autonomous system. Higher weight routes are the favored/preferred and only local router is influenced. Weight is the configurable parameter and Weight attribute can be configured as to change the weight of routes use the routes maps and other way to configured the weight attribute is to change the weight for all updates from the neighbor use the neighbor weight router configuration command. BGP route selection process prefers the highest weight. The default value of the weight attribute is 32768 and the range of the weight value is 0 to 65535.

Local Preference

Local preference is the second attribute of the border gateway protocol and this attribute is used only within the autonomous system to determine the best and valid path to leave the Autonomous system. So, the highest value of the local preference is preferable and the default value of the local preference is 100. This attribute is the attribute that is exchange between the IBGP neighbors. The local preference range is 0 to 4.29 billion and It can be configured with the help of the route map and the other way to change the default local preference for all the routes advertised by the router use command that below.

Self Originated

Self originated is the attribute that prefer locally originated paths.

AS Path

AS path is the other attribute that is most usable attribute of the border gateway protocol and this attribute preferred if it has the shortest AS path regardless of the available bandwidth. This attribute is the attribute that is used for the loop avoidance purpose.

Origin

Origin is the other attribute of the border gateway protocol and this attribute is preferring the IGP learned routes over EBGP and the EBGP over unknown.

MED

MED is used to for the deciding how to enter an autonomous system when multiple paths exist and when comparing the MED values for the same destination network in border gateway protocol path selection process in that case the lowest MED value is preferable. The default value of the MED attribute is 0. This attribute is evaluated late in the border gateway path selection process.

Externals

Prefer the EBGP routes over the IBGP.

IGP Cost

This attribute considered IGP metric that should be lowest.

EBGP Peering

This attribute favors the more stable routes and oldest routes are most preferable.

Router ID

This is the last attribute of the border gateway protocol which is known as the tie breaker and the lowest router ID is the preferable.