BGP Border Gateway Protocol - PowerPoint

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

   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

   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

   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

   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

   Verifying BGP Operation

   Configuring the ,….

   Verifying BGP Configuration
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)
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 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)
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.