CCNP Network Route BGP Part -I
BGP : Border Gateway Protocol. It is a distance vector
protocol
It is an External Gateway Protocol and basically used for
Internet.
BGP basically help communication possible between
routers on the internet.
BGP is mostly used by different organizations to make
sure their servers are highly available for internet users.
Their public addresses or routers can be advertised to
various ISP’s to make sure redundant and highly available
connections.
BGP can also decide which best path to use between
ISPs. This is called Multihoming.
CCNP Network Route BGP Part -I
BGP runs on TCP and uses port 179. BGP uses TCP because its
reliable. BGP only sends an update when a change occurs.
BGP is very slow but has the biggest metric & routing table of
all protocols. Tuning BGP with attributes is important other
wise it will use hop counts for best path irrespective of the
bandwidth or speed.
There are four kind of packets in BGP.
1. Open: It starts the BGP session
2. Keepalive: Its make sure neighbor is available.
3. Update: It make sure Network is reachable.
4. Notification: If an error occurs it notifies and closes the
session.
CCNP Network Route BGP Part -I
Tables:
Three kind of tables:
BGP Table: It consist of all BGP routes.
Routing Table: It consist of best routes.
Neighbor Table: It consist of configured neighbors, because
BGP does not configures neighbors automatically so we have to
do it manually, however BGP dynamic neighbor is an
exception.
Please visit www.cisco.com for more info about BGP Dynamic
Neighbors.
BGP supports two kind of subprotocols.
1. IGBP [ Internal]
2. EBGP [External]
CCNP Network Route BGP Part -I
Autonomous system: In BGP AS is very important. It basically
represents all networks in a specific group.
IBGP: is when a neighbor relationship is established between
two routers in the same AS or Autonomous System.
EBGP: is when a neighbor relationship is established between
two routers in different AS.
Note: For IBGP its not necessary to form neighbors only if the
routers are directly connected. It can form neighbors through
routers as well.
Transit AS: is when an ISP exchange route through our router
running BGP.
CCNP Network Route BGP Part -I
R1 with IP 192.168.10.1
R2 with IP 192.168.10.2
AS 1000 fro IGBP
CCNP Network Route BGP Part -I
Basic BGP Configuration:
R1(config)#router bgp 1000 
Now we have another router R2 and we wish to establish a neighbor
relationship with it for that we will use the following command on R1.
Note R1 has ip address of 192.168.10.1 and R2 has ip address of
192.168.10.2
R1(config-router)#neighbor 192.168.10.2 remote-as 1000 
But at the moment R2 is not configured so if type command:
R1(config-router)#do show ip bgp summary 
It will show the below:
BGP router identifier 192.168.10.1, local AS number 1000
BGP table version is 1, main routing table version 1
Neighbor
V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down
State/PfxRcd
192.168.10.2 4 1000
0
0
0 0 0 never Active
Note: Active is not good as it is finding routes and not working
CCNP Network Route BGP Part -I
Now on R2 we issue the below commands
R2(config-router)#neighbor 192.168.10.1 remote-as 1000
R2(config-router)#
*Mar 1 00:41:04.675: %BGP-5-ADJCHANGE: neighbor
192.168.10.1 Up
Now if we issue the same command on R1
R1(config-router)#do show ip bgp summary
BGP router identifier 192.168.10.1, local AS number 1000
BGP table version is 1, main routing table version 1
Neigh V AS MsgRcvd MsgSent
192.168.10.2 4 1000
7
TblVer InQ OutQ Up/Down State/p
7
1 0 0 00:03:06
0
Note: State has changed from Active to a number which is
good.
CCNP Network Route BGP Part -I
To create Neighbors with EGBP we only change AS which will
not be the same.