BGP Border Gateway Protocol By Amir and David

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BGP Border Gateway Protocol By Amir
and David
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What Is BGP ?

• Exterior gateway protocols are designed to route
  between autonomous systems.
• ASs 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 ASs
• Routers that belong to different ASs 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.

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BGP Operations

• BGP neighbors communicating between ASs must
  reside on the same physical network.
• Before it exchanges information with an external
  AS,BGP ensures that networks within the ASs 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.

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BGP Operations

• 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.

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BGP Operations

• 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

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BGP Operations

• 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..

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Basic BGP Configuration

• Verifying BGP Operation
• Configuring the ,.
• Verifying BGP Configuration

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BGP Configuration Steps

• activates the BGP protocol and identifies the
  local autonomous system
• LABA(config)router 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)

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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.

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The second step LABA(config-router)network
192.168.5.0 (network network-number) 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)
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Third step Define BGP neighbors LABA(config-route
r)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.
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LABA(config)router bgp 100 LABA(config-router)ne
twork 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

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Verifying BGP Configuration

• LABAshow ip bgp
• This command shows the BGP routing table.
• LABAshow 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
• LABAshow ip bgp neighbors
• The BGP Established field indicates a
  connection was made between router LABA and LABB.