BGP Path Attributes

Table of Contents

BGP uses BGP Path Attributes to determine the Best Path to a destination. According to BGP Best Path Algorithm, BGP Path Attributes are used to determine the BGP Best Path selection.

With these Path Attributes, network administrators can manage the BGP Traffic and determine way of the BGP traffic flow.

You can also test yourself on BGP Quizes Section for your BGP Path Attribute knowledge.

BGP Path Attributes divide into two groups. These classes are Well-Known and Optional path attributes. These two groups divide also into two subgroups again. These four BGP Path Attribute sub groups are:

* Well-Known Mandatory
* Well-Known Discretionary
* Optional Transtive
* Optional Non-Transitive

Well-Known BGP Path Attributes are supported on all BGP software implementations. And, Well-Known Mandatory Attributes are must be included in every BGP Update Message. But, Well-Known Discretionary Path Attributes may or may not appear in BGP Update Message, it is optional. The attributes name that are well-known are below:

* Well-Known Mandatory :AS Path, Origin, Next_Hop

* Well-Known Discretionary :Local Preference, Atomic_AggregateOptional BGP Path Attributes, may or may not be supported by all BGP implementations. Here, Optional Transtive Attributes are sent in an update message, but not recognized by the receiver, it should be passed on to the next AS. The Optional Non-transtive BGP Path Attributes may or may not be supported too, but if it received, it is not required that the router pass it on. It may safely and quietly ignore the optional attribute. The attributes name that are optional are below:

* Optional Transtive : Aggregator, Community

* Optional Non-transtive :Multi-Exit-Discriminator (MED) , Originator ID, Cluster List

There is also one extra important BGP Path Attribute. This attribute is,

Cisco Proprietary, BGP Weight Attribute.BGP Weight Attribute is only used on Cisco router and it is the first step of BGP Path Selection algorithm for Cisco devices.

You can also test yourself on BGP Quizes Section for your BGP Path Attribute knowledge.