This is required blogging…and reading for that matter.  A good chunk of this is taken from my CCNP posts from last year.  Corrections, please.

How does a BGP router decide which BGP route is the best?

Next-hop : Does the router have a route to the next-hop?

Weight : This is a numeric value where bigger is better.  Weight is not passed onto other peers and is a Cisco proprietary feature.

Make my corrections!  Please!

Well-known mandatory : These PAs must be recognized by all BGP routers and passed along to other peers.

Well-known discretionary : These PAs do not need to be in every update, but they must be recognized by all BGP routers.

Optional transitive : These PAs don’t have to be recognized but they must be passed along to other BGP peers if they are present in an update.

Corrigeme, por favor.

Open : When a neighbor is configured, the router sends an open to that neighbor to get the ball rolling.

Destination:  The neighbor's configured IP
Important fields:
  My AS

Update : The routing  information

Destination:  The neighbor's configured IP
Important fields:
  Advertised network Klonopin Online
  Path attributes

Keepalive : Sent every 60 seconds by default

Destination:  The neighbor's configured IP
Important fields:
  Nothing, really

Notification : When something is amiss, the router sends a notification message.  The receiver then closes the connection.

Corrections appreciated.

Idle : There is no relationship, but the router sends out a TCP SYN to the neighbor to get the ball rolling.

Idle (admin) : The neighbor is admined down.

Connect : The router is waiting for the TCP connection to finish.  If the TCP connection finishes, the router sends an open and transitions to OpenSent.  If it times out, it transitions to Active.

Active : The router tries Cialis to initiate a TCP connection.  If the TCP connection finishes, the router sends an open and transitions to OpenSent.

Per the standard rules, please correct anything that’s wrong.

One of EIGRP’s big features is the ability to use unequal cost paths for load balancing.  This is done with the variance command.

variance : A multiplier used to calculate which feasible successors can be used as active routes.  The router takes integer and multiplies it by the successor’s feasible distance, and any FS with a an FD less than this new number gets submitted to the routing table manager.

Please correct if I’m being stupid…which is a lot of the time.

Hello : Discovers and maintains neighbors

Destination:  224.0.0.10
Important fields:
  K values

Update : An update to the topology such as a route withdrawal or a metric change

Destination:  224.0.0.10 -or- unicast during neighbor discovery
Important fields:
  Message sequence number
  Route being updated including k values to compute metric

Query : Used to ask a neighbor if it has a route to a certain network; see casino online for free stuck-in-active

Corrections are always welcome.

Broadcast : Think an Ethernet segement

DR/BDR? : Yes Default hello interval : 10 sec Neighbor config required? : No

Point-to-point : Physical point-to-point links, frame-relay point-to-point subifs

DR/BDR? : No Default hello interval : 10 sec Neighbor config required? : No

Nonbroadcast Multiaccess : Frame-relay multipoint or physical

DR/BDR? : Yes Default hello interval : 30 sec Neighbor config required? : Yes

Point-to-multipoint : Partial mesh networks like a frame-relay hub-and-spoke configuration