Cisco IOS default management lines: By default, how many simultaneous Telnet (VTY) sessions does a Cisco router support?

Introduction / Context:
Remote CLI access to Cisco routers and switches is provided via virtual terminal (VTY) lines. Knowing the default number of VTY lines helps plan concurrent administrative access and configure AAA, access-class filters, and transport settings.

Given Data / Assumptions:

• Default IOS configurations typically create VTY lines 0 through 4.
• Each VTY line can service one active remote session (Telnet or SSH).
• Platforms may allow adding more VTYs, but defaults matter for exams and baselines.

Concept / Approach:
If VTY lines are numbered 0,1,2,3,4, that yields five concurrent sessions. Administrators can view this with show running-config which lists a line vty 0 4 stanza by default.

Step-by-Step Solution:

Verification / Alternative check:
Issue show line or show users to verify active lines and sessions. Config guides show the default block as 0 4.

Why Other Options Are Wrong:

• 2, 3, 4: underestimate default capacity.
• 16: corresponds to a common custom configuration (0 15) but is not the default.

Common Pitfalls:
Confusing console/aux lines with VTY lines; forgetting to secure all VTYs with passwords or AAA, leaving some lines open.

Final Answer:
5