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350-501 Networking Practice Question

Exhibit

Refer to the exhibit.

R1# show ip bgp neighbors 10.0.0.1
BGP neighbor is 10.0.0.1, remote AS 65000, external link
  BGP version 4, remote router ID 10.0.0.1
  BGP state = IDLE
  Last read 00:00:00, last write 00:00:00
  Hold time is 180, keepalive interval is 60 seconds
  Message statistics:
    InQ depth is 0
    OutQ depth is 0
    Sent: total 0, updates 0
    Received: total 0, updates 0
  Connections established 0; dropped 0
  Last reset never
  External BGP neighbor may be up to 255 hops away.
  Connection is not permitted by TTL security check (TTL=1)

Based on the exhibit, what is preventing the BGP session from establishing?

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

The TTL security check is blocking the connection

The error message indicates the TTL security check is rejecting the connection because the incoming TTL is not 255 (as expected for an eBGP multihop session). The remote AS is shown as 65000, so it is eBGP. The neighbor is reached via a single-hop but the TTL check expects TTL=255, but the router sees a TTL less than that. Option A is wrong because no MD5 password mismatch is indicated; the error explicitly mentions TTL security. Option B is wrong because the update-source is not the issue; the TTL check is the direct cause. Option C is wrong because the error message does not mention prefix limits; it clearly states TTL security.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
The BGP MD5 password is mismatched
Why it's wrong here
There is no indication of an MD5 authentication error.
✗
The BGP update-source is misconfigured
Why it's wrong here
No evidence of update-source issue; the error is specific to TTL.
✗
The neighbor has reached its maximum prefix limit
Why it's wrong here
No prefix limit error is shown; the state is IDLE due to TTL security.
✓
The TTL security check is blocking the connection
Why this is correct
The error 'Connection is not permitted by TTL security check (TTL=1)' clearly indicates the TTL security mechanism is rejecting the packet.

Go deeper

350-501 Networking Practice Question

Exhibit

Why each option matters

Option-by-option breakdown

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