BGP attributes is a metric used to describe the
characteristics of a BGP paths. Attributes are conatained in
update messages passed between BGP peers for advertise routers.

BGP attributes are broadly divided into two types - 

a) Well Known          
b) Optional.


Well Known attributes are divided into two types - 

a) Mandatory            
b) Descretionary 

** Mandatory attributes are divided into three types - 

a) AS Path      
b) Next Hop       
c) Origin

** Origin attributes divided into three types - 

a) Internal(i)     
b) External(e)   
c) Incomplete(?)

** Descretionary attributes are divided into two types - 

a) Local Preference         
b) Atomic Aggregate



Optional attributes are divided into two types - 

a) Transitive                
b) Non Transitive


** Transitive attributes are divided into two types - 

a) Aggregator                
b) Community


** Community attributes are divided into for types - 

a) No-export
b) No advertise
c) Internet
d) Local AS.

&& Non transitive attributes are divided into three types - 

a) MED (Multi Exit Discriminator).
b) Originator
d) Cluster ID.




I'll explain all attributes on next post..!!!

Lets start from first... I m gonna explain each attributes
one by one - 

Well Known: 
           Well known attributes are must be recognized by
each compliant of BGP implementations. Well known attributes
are propagated to other neighbors also.

Optional:
         Optional attributes are recognized by some
implementation of BGP & expected that not recognized by
everyone. Optional attributes are propagated to their
neighbors based on the meanings.


Mandatory:
          Mandatory is BGP well known attributes. Mandatory
attributes are must be present in all update message passed
between BGP peers. It is present in route description.

Discretionary:
              Discretionary is BGP well known attributes.
Discretionary attributes are may be present on update message.

AS Path: 
        AS path is BGP well known mandatory attributes. AS
path defines the list of Autonomous System that a route has
passed through. AS path attributes are used in path
selection process & lowest path attributes will be preferred
over highest one.

Next-Hop:
         Next hop is BGP well known mandatory attributes. In
BGP, next hop is the IP address which is used to reach the
advertising BGP router. 

For EBGP, next hop is the ip address of the connection
between the peers. 

For IBGP, EBGP next hop address is carried into local
autonomous system.

Origin:
       Origin is BGP well known mandatory attributes.
Origion attributes define how BGP router learned about the
particular route. Origin attribute have three possible
values i.e. internal (i), External (e) & Incomplete (?).

Internal(i):
            BGP learned about the route from Interior
routing protocol.

External(e):
             BGP learned about the router from External BGP.

Incomplete(?):
            The origin of the route is unknown or learned by
some other way. The origin of incomplete occurs when routes
are redistributed into BGP.



NB: 
1. Due to lack of time, rest of attributes I'll discuss on
next post. 
2. Its little bit difficult to draw diagram here & explain
each & every attributes.
3. If anyone need more about this, mail me on
mr.shahin07@gmail.com

Thanks & enjoys the weekend party tonight.... hehehe

BGP attributes are path manipulation features of BGP.There are 
many attributes : AS-path, MED, Local preference, Weight, and 
Origin code