Cisco CCNP BSCI Exam Tutorial BGP Adjacency States
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Cisco CCNP / BSCI Exam Tutorial: Understanding BGP Adjacency States
To excel in the BSCI exam and achieve your CCNP certification, mastering Border Gateway Protocol (BGP) is essential. One fundamental aspect you need to understand is the BGP adjacency states. Let's dive into these states with insights from Chris Bryant, CCIE
12933.
BGP Adjacency Process
Understanding BGP adjacency states is crucial for analyzing and troubleshooting peer relationships. Let's illustrate this with an example of creating a BGP peer between R1 and R3:
```plaintext
R1(config-router)
neighbor 172.12.123.3 remote-as 200
```It's important to note that BGP peers do not have to be in the same Autonomous System (AS). To verify the peer status, use the command:
```plaintext
R1
show ip bgp neighbor
```Example Output
```plaintext
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
```
Initially, this might seem promising, but the "Active" state indicates that no peer connection has been established yet. Let's explore the different BGP states:
BGP States Explained
1. Idle: The initial state where BGP waits for a connection event. Once a TCP connection is established, the process moves forward.
2. Connect: If the TCP handshake is successful, BGP transitions to the OpenSent state. If not, it shifts to Active.
3. Active: Here, BGP attempts to form a peer relationship. Successful completion transitions BGP to OpenSent. Frequent flapping between Active and Connect may indicate issues with the physical connection or configurations.
4. OpenSent: The BGP speaker has received an Open message. It checks whether the peer is within the same AS (iBGP) or a different one (eBGP).
5. OpenConfirm: BGP awaits a keepalive message. Upon receipt, the state changes to Established, finalizing the neighbor relationship.
6. Established: Now, update packets can be exchanged.
Even though the "Active" state seems positive, it means we need further configurations. In our example, R3 hasn't been configured yet:
```plaintext
R3(config)
router bgp 200
R3(config-router)neighbor 172.12.123.1 remote-as 100
```Verify the successful establishment with:
```plaintext
R3
show ip bgp neighbor
```Confirmed Output
```plaintext
BGP neighbor is 172.12.123.1, remote AS 100, external link
BGP state = Established, up for 00:01:18
```
Now, the peer relationship between R1 and R3 is successfully established!
By understanding these states, you can effectively analyze and troubleshoot BGP connections, aiding your success in the BSCI exam and your journey to becoming an expert networker.
You can find the original non-AI version of this article here: Cisco CCNP BSCI Exam Tutorial BGP Adjacency States.
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