Transcript Border Gateway Protocol (BGP)

Border Gateway Protocol (BGP)
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BGP
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What
Why
Who
When
Where
BGP Version 4
• RFC 1771
• Intelligent route selection
based on most specific prefix
and shortest Autonomous
System (AS) path
• Classless Inter Domain
Routing (CIDR)
• Current Internet standard for
inter-domain (AS) exterior
routing
Border Gateway Protocol (BGP)
• Used for carrying routing
information between AS’s
• Path vector protocol
• Incremental
• Runs over TCP (port 179)
• Conveys information about AS
path topology
General Operation
• Learns multiple paths via
internal and external BGP
speakers
• Picks the best path and installs
in the IP forwarding table
• Policies applied by influencing
the best path selection
When should I use BGP?
• Dual- or multi-homed
• Providing partial or full internet
routing to a downstream
customer
• Anytime the AS path
information is required
BGP is not needed…
• … if singularly homed
• … if not providing downstream
routing
• Use a default route!
Load Balancing
• BGP itself does not loadbalance traffic; it chooses &
installs a “best” route.
BGP Load Balancing Problem
• “Since BGP picks a ‘best’ route
based upon most specific
prefix and shortest AS_PATH, it
becomes non-trivial to figure
out how to manually direct
specific portions of internal
traffic (prefixes) in a distributed
fashion across multiple
external gateways.”
Asymmetric Routing Paradigm
• In the Internet, it is impossible
to control end-to-end routing
and paths traversed
• Packets may not always
traverse the same downstream
path as they do when
forwarded upstream
Summary
• Use BGP only when needed!
• IGP and conventional BGP
network problems
• BGP gives flexibility and
control