Difference between revisions of "BGP"
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Revision as of 04:26, 21 May 2020
Contents
BGP Basics
https://academy.apnic.net/en/virtual-labs/ https://www.juniper.net/documentation/software/erx/erx41x/swconfig-routing-vol2/html/bgp-config.html
RFC 4271
- IBGP - Carry summarised network routes across an AS
- EBGP - Exchange summarised network routes between different AS
IBGP does not need to be directly connected - generally uses the loopback address.
IBGP doesnt advertise routes learned from other IBGP nodes (only ebgp) - thus all nodes need to learn - thus where a route reflector comes into play
4 Messages
- OPEN - Hello - must have router id, AS #
- KEEPALIVE - Heartbeat
- UPDATE - Carries routes and deletes
- NOTIFICATION - Error - Connection is closed immedately
States
- Idle (trying to initiate a TCP connection with the BGP Peer)
- Connect (3way TCP handshake)
- Open Sent (connect sent but not confirmed)
- Active
- Open Confirm (BGP waits for a Keepalive or Notification message)
- Established (BGP session is established. BGP neighbors exchange routes via Update messages)
Path Attributes
Well-known Mandatory
Requried in every update message
- ORIGIN
- AS_PATH
- NEXT_HOP
Well-known discretionary
- LOCAL_PREF
- ATOMIC_AGGREGATE
Optional transitive
- AGGREGATOR
- COMMUNITY
Optional non-transitive
- MULTI_EXIT_DISC
- ORIGINATOR_ID
- CLUSTER_LIST