BGP Flashcards
Neighbor establishment port
TCP port 179
BGP message types
Open: Initiates connection and sends AS number, router ID, capabilities
Keepalive: Default interval is 60 seconds
Update: New or withdrawn routing info
Notification: Sent if error occurs
BGP session states
Idle
Connect
Active
OpenSent
OpenConfirm
Established
Idle state
Initial state, no connection made
Connect state
Attempts to establish TCP connection
Active state
Retries connection if unsuccessful
Opensent state
Open message sent, waiting for response
Openconfirm state
Open response received, keepalives exchanged
Established
Peers are fully connected and routes are exchanged
Stuck in idle
misconfigured peer IP or AS
TCP 179 blocked
No connectivity
CPU limitations
Stuck in connect
Peer not responding to TCP connection request
Peer IP address or port not reachable
Passive mode enabled on both peer where neither peer initiates the connection
Stuck in active
Connectivity issues
No matching BGP config
TCP session timing out due to firewall or slow network
Stuck in opensent
Mismatched AS number, BGP version, authentication
Peer not responding
Router drops open message due to corruption or incorrect settings
Stuck in openconfirm
Peer not sending keepalive, maybe misconfigured timers
Network instability
Router software or hardware issues
Attributes in order
Weight
Local Preference
Locally Originated
AS Path Length
Origin Type
Multi-Exit Discriminator (MED)
eBGP over iBGP
IGP Metric
Router ID
Neighbor Address
Communities
No-export - Don’t advertise outside local AS
No-advertise - Don’t advertise to peers
Local-as - Don’t advertise to eBGP peers, only iBGP
Set communities on routes using route maps or policies
Route-reflector
Solves full-mesh iBGP problem by creating a central route-sharing point
Confederations
Solves full-mesh iBGP problem by splitting the AS into sub-ASes, where the members in the confederation use iBGP within their sub-AS and eBGP outside their sub-AS. The outside views the confederation as one AS
