CCNP Certification / BSCI Exam Tutorial: The BGP Neighbor Process
Computer and Technology - Like TCP, BGP is connection-oriented. An underlying connection between two BGP speakers is established before any routing details are exchanged. This connection happens on TCP port 179. Just like EIGRP and OSPF, keepalive messages are sent out from the BGP speakers to keep this relationship alive.
When the connection is established, the BGP speakers exchange routes and synchronize their tables. After this initial exchange, a BGP speaker will only send further updates upon a change inside the network topology.
The IGP protocols which use Autonomous Systems, IGRP, and EIGRP, require prospective neighbors to become inside the same AS. This Isn‘t true with BGP. Routers could be in several Autonomous Systems but still exchange routes. The BGP neighbors don‘t have to be directly connected, and sometimes aren‘t, but do need to reach the IP addresses they use with their neighbor statements.
A BGP peer that‘s inside the same AS is mentioned being an Internal BGP (eBGP) Peer, where a BGP peer in another AS is an External BGP (eBGP) Peer.
A sample iBGP configuration :
Router bgp 100
Neighbor 10. 1. 1. 2 remote-as 100
A sample eBGP configuration :
Router bgp 100
Neighbor 10. 1. 1. 2 remote-as 200
Cisco recommends that eBGP peers be directly connected, where eBGP peers generally won‘t be.
Before we calculate an excessive amount farther into BGP theory, let’s obtain a configuration started. You’ll utilize the router bgp command to configure a router like a BGP speaker. Right after that, the neighbor command will certainly be designed to identify this BGP speaker’s potential neighbors. (The terms "peer" and "neighbor" are interchangeable in BGP, but it is the neighbor statement that is designed to statically define neighbors. BGP Isn‘t proficient at discovering neighbors dynamically. )
R1 (config-router ) #neighbor 172. 12. 123. 3 remote-as 200
While almost all the neighbor options are just that -- optional -- you are doing need to specify the BGP AS from the remote router. BGP has no mechanism to dynamically discover neighbors. Remember, BGP speakers don‘t have to be inside the same AS to get peers. To verify the remote BGP speaker has turned into a peer, run show ip BGP neighbor.
R1#show ip BGP neighbor
BGP neighbor is 172. 12. 123. 3, remote AS 200, external link
BGP version 4, remote router ID 0. 0. 0. 0
BGP state = Active
Last read 00: 01: 39, hold time is 180, keepalive interval is 60 seconds
Received 0 messages, 0 notifications, 0 in queue
Sent 0 messages, 0 notifications, 0 in queue
Route refresh request: received 0, sent 0
Default minimum time between advertisement runs is 30 seconds
The output here may be a little misleading the very first time you read through it. The very first highlighted line shows 172. 12. 123. Three is a BGP neighbor, is located in AS 200, and it is an external link, indicating the neighbor is in another AS entirely. The next highlighted line shows the BGP state as Active. This sounds great. However, it means that the BGP peer connection doesn‘t yet exist using the prospective neighbor.
So although show ip BGP neighbor output indicated that this is an Active neighbor relationship, that’s not as good because it sounds. In fact, the rationale the peer relationship hasn’t been established is that many of us haven’t configured R3 yet!
R3 (config ) #router bgp 200
R3 (config-router ) #neighbor 172. 12. 123. 1 remote-as 100
Verify the peer establishment with show ip BGP neighbor :
R3#show ip BGP neighbor
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 : 01 : 18
Last read 00: 00: 17, hold time is 180, keepalive interval is 60 seconds
Local host: 172. 12. 123. 3, Local port: 179 (BGP uses TCP Port 179 )
Foreign host: 172. 12. 123. 1, Foreign port: 11007
The peer relationship between R1 and R3 is established.
Once you are aware how the neighbor relationship is built, you have to start learning the many options from the neighbor command. You’ll need to master these to turn into a CCNP and CCIE!
I think it's enough all about CCNP Certification / BSCI Exam Tutorial: The BGP Neighbor Process. Thanks so much :)
CCNP Certification / BSCI Exam Tutorial: The BGP Neighbor Process
The IGP protocols which use Autonomous Systems, IGRP, and EIGRP, require prospective neighbors to become inside the same AS. This Isn‘t true with BGP. Routers could be in several Autonomous Systems but still exchange routes. The BGP neighbors don‘t have to be directly connected, and sometimes aren‘t, but do need to reach the IP addresses they use with their neighbor statements.
A BGP peer that‘s inside the same AS is mentioned being an Internal BGP (eBGP) Peer, where a BGP peer in another AS is an External BGP (eBGP) Peer.
A sample iBGP configuration :
Router bgp 100
Neighbor 10. 1. 1. 2 remote-as 100
A sample eBGP configuration :
Router bgp 100
Neighbor 10. 1. 1. 2 remote-as 200
Cisco recommends that eBGP peers be directly connected, where eBGP peers generally won‘t be.
Before we calculate an excessive amount farther into BGP theory, let’s obtain a configuration started. You’ll utilize the router bgp command to configure a router like a BGP speaker. Right after that, the neighbor command will certainly be designed to identify this BGP speaker’s potential neighbors. (The terms "peer" and "neighbor" are interchangeable in BGP, but it is the neighbor statement that is designed to statically define neighbors. BGP Isn‘t proficient at discovering neighbors dynamically. )
R1 (config-router ) #neighbor 172. 12. 123. 3 remote-as 200
While almost all the neighbor options are just that -- optional -- you are doing need to specify the BGP AS from the remote router. BGP has no mechanism to dynamically discover neighbors. Remember, BGP speakers don‘t have to be inside the same AS to get peers. To verify the remote BGP speaker has turned into a peer, run show ip BGP neighbor.
R1#show ip BGP neighbor
BGP neighbor is 172. 12. 123. 3, remote AS 200, external link
BGP version 4, remote router ID 0. 0. 0. 0
BGP state = Active
Last read 00: 01: 39, hold time is 180, keepalive interval is 60 seconds
Received 0 messages, 0 notifications, 0 in queue
Sent 0 messages, 0 notifications, 0 in queue
Route refresh request: received 0, sent 0
Default minimum time between advertisement runs is 30 seconds
The output here may be a little misleading the very first time you read through it. The very first highlighted line shows 172. 12. 123. Three is a BGP neighbor, is located in AS 200, and it is an external link, indicating the neighbor is in another AS entirely. The next highlighted line shows the BGP state as Active. This sounds great. However, it means that the BGP peer connection doesn‘t yet exist using the prospective neighbor.
So although show ip BGP neighbor output indicated that this is an Active neighbor relationship, that’s not as good because it sounds. In fact, the rationale the peer relationship hasn’t been established is that many of us haven’t configured R3 yet!
R3 (config ) #router bgp 200
R3 (config-router ) #neighbor 172. 12. 123. 1 remote-as 100
Verify the peer establishment with show ip BGP neighbor :
R3#show ip BGP neighbor
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 : 01 : 18
Last read 00: 00: 17, hold time is 180, keepalive interval is 60 seconds
Local host: 172. 12. 123. 3, Local port: 179 (BGP uses TCP Port 179 )
Foreign host: 172. 12. 123. 1, Foreign port: 11007
The peer relationship between R1 and R3 is established.
Once you are aware how the neighbor relationship is built, you have to start learning the many options from the neighbor command. You’ll need to master these to turn into a CCNP and CCIE!
I think it's enough all about CCNP Certification / BSCI Exam Tutorial: The BGP Neighbor Process. Thanks so much :)
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