See [BGPNotes]%%% 

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 !!BGP Terms 

  

 |Aggregation|The BGP term for summarization. 

 |Attribute|Similar to metric, these are variables that describe characteristics of the path to the destination. Once difined, the characteristics can be used to make decision as to which path should be taken, based on the characteristic or attribute of the paths available. 

 |Autonomous System|Definition for the organizational boundary. Routers share the same routing protocol within the organization. The autonomous system defines all the router within an administrative domain, where each router has full knowledge of the subnets within the domain. If you are connecting directly to the Internet using BGP, the autonomous system number must be unique from the Internet addressing committees. 

 |Exterior Gateway Protocol (EGP)|The generic term for a protocol that runs between autonomous systems. There is also a specific protocol with this name, which was the precursor to BGP. 

 |Route reflector client|A client is a router that has a TCP session with its iBGP peer that is acting as a route reflector. It forwards routes to the route reflector, which propagates these on to other routers. The client does not have peer connections with other clients. 

 |Route reflector cluster|A cluster is a group consisting of a route reflector and clients. There can be more than one route reflector in a cluster. 

 |Synchronization rule|This rule states that a router cannot forward a route to an eBGP peer unless the route is in its local IP routing table. This requires that the IGP and BGP routing tables are synchronized. This is to prevent BGP from advertising routes that the autonomous system cannot cirect to the destination.%%%If BGP is fully meshed, it does not have to rely on the IGP routing tables and you can disable synchronization.%%%Use the ''Router(config-router)#__no synchronization__'' command to turn off synchronization. 

 |Transit autonomous system|An autonomous system that is used to carry BGP traffic across to another autonomous system. None of the traffic is destined for any router within the transit autonomous system; it is simply being routed through it. 

  

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 !!BGP Attributes 

  

 |__Category__|__Description__ 

 |__Well-known:__ 

 |Mandatory|These attributes are required and are therefore recognized by all BGP implementations. 

 |Discretionary|It is not required that these attributes be present in the update messages, but if they are present, all routers running BGP will recognize and act on the information contained. 

 |__Optional:__ 

 |Transitive|The router might not recognize these attributes, but if this is the case, it marks the update as partial and sends the update, complete with attributes, to the next router. The attributes traverse the router unchanged, if they are not recognised. 

 |Nontransitive|Nontransitive attributes are dropped if they fall onto a router that does not understand or recognize the attribute. 

 %%% 

 |__Attribute Name__|__Category__|__Code__|__Preference__ 

 |Origin|Well-known, mandatory|1|Lowest origin code.%%% %%%IGP < EGP < Incomplete 

 |AS_Path|Well-known, mandatory|2|Shortest path 

 |Next Hop|Well-know, mandatory|3|Shortest part or IGP metric 

 |Community|Optional, transitive|8|Information not used in path slection 

 |Originator ID|Optional, nontransitive|9|Information not used in path selection 

 |Cluster ID|Optional, nontransitive|10|Information not used in path selection 

 |Weight|Cisco-defined| |Highest value 

  

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 CategoryProtocols