BGP basic documentation ( from christ bryan udemy )

bgp?


" an internet protocol that allows group of routers (AS) to share routing information so that efficient, loop-free routes can be established.  "

^ biasanya digunakan di routing antar ISP.
^ masuk dalam kategori EGP / exterior gateway protocol





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BGP :
- support VLSM and summarization
- will send full updates when router first become neighbor, then partial upgrade reflecting latest network change
- create neighbor adjacencies alive. -> no keepalive = adjacencies gone.


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BGP should be used:
- company connecting more than one AS / ISP.
  ^ decision on best link / path is by BGP path attributes.
- routing policy of your organization and your ISP differ.
- when ur company is an ISP. when traffic from other AS use your AS as transit domain. (BGP needed! ).


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BGP should not be used:
- when there is a single connection to internet / another AS and no redundant link exist
- when u dont care which path is used to reach a route in another AS
- when router resources are limited  ( memory / cpu )


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BGP Peering Process
- connection oriented ( reliable )
- TCP port 179   !! dont block on acl !!
- exchanges full routes and sync tables, afterward bgp speaker will send further updates only upon change in network


- dont have to be in same AS in order become neighbor / exchange routes.
- BGP adjacencies called " peerings ", BGP peer in same AS  = iBGP peer.


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BGP AS100
R1-------------------R2


^ iBGP


-------------------------------------
cisco recommended eBGP peers = directly connected
iBGP peer are not required to be so connected.





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eBGP

AS100 AS300
R1----------------R3



R1
#conf t
#router bgp 100
#neighbor 172.12.123.3 remote-AS 300

#show ip bgp neigh
!! bgp neighor is 172.12.123.3, remote AS 300, external link  !!    -> info plg penting
!! bgp state = Active !!


** bgp state
- active = indicates bgp peer connection that does not yet fully exists  / does not complete / attempt to peering
- idle  = initial state of bgp peering
- Connect follows idle    = tcp connection request has been sent but response has not yet been received.

- Idle = if short = normal if stay idle, check remote router's neighbor statement and make sure AS number correct!

- OpenSent  = tcp connection complete  ( bgp will determines iBGP / eBGP  =  same as/different AS )


R3
#conf t
#router bgp 300
#neighbor 172.12.123.1 remote-AS 100

# show ip bgp neighbor 172.12.123.1

^

!! bgp neighbor is 172.12.123.1, remote AS 100, external link       
!! BGP version 4, remote router ID 172.12.123.1
!! BGP state = Established, up for 00:00:21
!! connection establised 1; dropped 0
!! last reset never

!! local host : 172.12.123.3, local port: 179
!! Foreign host: 172.12.123.1, Foreign port: 28861


^ informasi yg penting ^







R2
#conf t
#router bgp 300

R3
#conf t
#router bgp 100





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