BGP Flashcards
What type of routing protocol is BGP
Path Vector
eBGP AD
20
IBGP AD
200
BGP protocol
IP
BGP transport
TCP 179
BGP authentication
md5
What is an BGP AS
Autonomous System
What is an Autonoumous System
A logical domain under the control of a single entity
What is External BGP
BGP adjacencies that span AS boundries
What is Internal BGP
BGP adjacendies formed within a single AS
What is the “BGP Synchronization” requirement
A route must be known by an IGP before it will be advertised to BGP peers
Four BGP packet types (O,U,K,N)
Open, Update, Keepalive, Notification
BGP Neighbor states (I,A,C,OS,OC,E)
Idle, Active, Connect, Open Sent, Open Confirm, Established
BGP neighbor state: Idle
Neighbor is not responding
BGP neighbor state: Active
Attempting to connect
BGP neighbor state: Connect
TCP session established
BGP neighbor state: Open Sent
Open message sent
BGP neighbor state: Open Confirm
Open message received
BGP neighbor state: Established
Adjacency established
BGP attribute types
Well-known mandatory, well-known discrationary, optional transitive, optional non-transitive
Well-known mandatory attributes (O,A,N)
Origin, AS path, Next Hop
Well-known discretionary attributes (LP, AA)
Local preference, Atomic Aggregate
Optional Transitive attributes (A,C)
Aggregator, Community
Optional non-transitive attributes (M,O,CL,CI)
MED, Originator ID, Cluster List, Cluster ID
Well-known mandatory description
Must be supported and propagated
Well-known discretionary description
Must be supported, propagation optional
Optional Transitive description
Marked as partial if not understood by neighbor but will be passed on to it’s next neighbor
Optional non-transitive description
Deleted by neighbor if unsupported by neighbor and not passed on to it’s peer/neighbor
Attribute description: Origin
IGP, EGP or unkown
Attribute description: AS Path
List of AS which the advertisement has traversed
Attribute description: Next Hop
External peer in neighboring AS
Attribute description: Local Preference
Metric for internal neighbors to reach external destinations. (default 100)
Attribute description: Atomic Aggregate
Includes AS’s that were dropped due to route aggregation
Attribute description: Multiple Exit Descriminator
MED, Metric for external neighbors to reach local AS (default 0)
Attribute description: Weight
The BGP’s Weight Path attribute is the first path attribute BGP checks in the election of the best path in the BGP table on Cisco IOS Routers. BGP prefers the path for the entry with the highest Weight. Weight is a Cisco-specific parameter and it is only locally significant in the Router where it is configured.
3 commands needed for eBGP
neighbor x.x.x.x remote-as xxxxx
neighbor x.x.x.x update-source loopback0
neighbor x.x.x.x ebgp-multihop 2
