Border Gateway Protocol (BGP)

hardsweetlipsNetworking and Communications

Oct 28, 2013 (3 years and 10 months ago)

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Border Gateway Protocol (BGP)

Moving

Data…
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BGP


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

load
-
balance 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