Download BGP

BGP
Border Gateway Protocol
By Amir and David
What Is BGP ?
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Exterior gateway protocols are designed to route
between autonomous systems.
AS’s : A set of routers that operate under the same
administration and share a common routing strategy.
Bgp can be used for routing packets both within and
between AS’s
Routers that belong to different AS’s and exchange BGP
updates are running External BGP.These routers are
usually adjacent to each other and share the same
physical media and subnet.
Routers that belong to the same AS and exchange BGP
updates are running Internal BGP.
BGP Operations
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BGP neighbors communicating between AS’s
must reside on the same physical network.
Before it exchanges information with an external
AS,BGP ensures that networks within the AS’s
are reachable.
It does this by a combination of internal peering
among routers within the same As.
It redistributes BGP routing information to
interior gateway protocols such as RIP and
OSPF.
BGP Operations
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BGP uses TCP
When 2 routers running BGP form a TCP
connection they exchange messages to open
and confirm the connection parameters
Initial dat exchange between 2 bgp routers is
the entire BGP routing table.This is known as
an open message.
An open message must be confirmed before
updates notifications and keepalives can be
exchanged.
BGP Operations
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BGP does not require a periodic refresh of the
entire routing table.
Routers instead receive incremental updates
that contain the latest version of each peers
routing table.
Incremental updates are sent out as the routing
tables change.
BGP update messages contain network
numbers and path pairs
BGP Operations
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Bgp maintains a routing table with all feasible
paths to a particular network.
It advertises only the optimal path in its update
messages based on metrics assigned by the
network admin through the use of config files.
BGP metrics may be based on any number of
criteria including AS hop count,type of
link,bandwidth,and path cost..
Basic BGP Configuration
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Verifying BGP Operation
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Configuring the ,….
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Verifying BGP Configuration
BGP Configuration Steps
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activates the BGP protocol and identifies the
local autonomous system
 LABA(config)#router
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bgp 100 .
permits BGP to advertise a network
 LABA(config-router)#network
192.168.5.0
(network network-number)
The network command creates the route in the
BGP table only if the routes are already
present in the IP routing table)
BGP Configuration Steps
The first step to activate BGP
Start in config mode.
LABA(config)#router bgp 100 (router bgp autonomous-system)
This activates the BGP protocol and identifiesthe local autonomous
system the router belongs to.
The second step
LABA(config-router)#network 192.168.5.0 (network networknumber)
This command permits BGP to advertise a network if the
network is listed in the IP routing table.
The network command creates the route in the BGP table only
if the routes are already present in the IP routing table)
Third step
Define BGP neighbors
LABA(config-router)#neighbor 172.16.66.1 remote-as 200
(neighbor ip-address remote-as autonomous system)
The neighbor part of the command indicates the routers to which we
are trying to connect to using BGP.The IP address is the next hop
directly connected address.(This is usually the IP address of the
interface at the other end of the connection) .
The remote-as autonomous system identifies the AS numberof the
router to which we are trying to connect using BGP.
The value placed in the autonomous-system part of the command
determines whether the communication between the neighbor is an
EBGP or an IBGP session.
LABA(config)#router bgp 100
LABA(config-router)#network 192.168.5.0
LABA(config-router)#neighbor 172.16.66.1 remote-as 200
LABA(config-router)#exit
LABB (config)#router bgp 200
LABB(config-router)#network 172.16.0.0
LABB(config-router)#neighbor 172.16.66.2 remote-as 200
LABB(config-router)#exit
Verifying BGP Configuration
LABA#show ip bgp
This command shows the BGP routing table.
LABA#show ip route
This command will show the ip routing table and should show the route
that was learned through BGP.
To check that a neighbor connection is up use the show ip bgp neighbors
command
LABA#show ip bgp neighbors
The BGP = Established field indicates a connection was made between
router LABA and LABB.