Fortinet
FCSS_NST_SE-7.4 · Question #80
Refer to the exhibit, which shows the output of a BGP debug command. Why has the local router at 172.16.23.58 been unable to establish adjacency with its only neighbor?
The correct answer is C. The local router has not received a SYN/ACK packet from the neighbor. In BGP's Connect state the router has sent the initial TCP SYN but hasn't received the SYN/ACK from its peer, so the TCP handshake never completes and adjacency can't form.
Routing and Policy Troubleshooting
Question
Refer to the exhibit, which shows the output of a BGP debug command. Why has the local router at 172.16.23.58 been unable to establish adjacency with its only neighbor?
Exhibit
Options
- AThe local router has not received a keepalive message from the neighbor.
- BThere is no active route to the BGP neighbor.
- CThe local router has not received a SYN/ACK packet from the neighbor.
- DThe local router has not received an OPEN message from the neighbor.
How the community answered
(29 responses)- A3% (1)
- B10% (3)
- C83% (24)
- D3% (1)
Explanation
In BGP's Connect state the router has sent the initial TCP SYN but hasn't received the SYN/ACK from its peer, so the TCP handshake never completes and adjacency can't form.
Topics
#BGP adjacency#TCP three-way handshake#BGP debug#SYN/ACK
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