ECMS Practice Question - Nov/2nd

[RafaelM]

ECMS question

In a topology consisting of 2 MX hubs with 2 uplinks each and 20 MX spokes with 1 uplink each, how many AutoVPN tunnels are created in total in this organization? Assume all spokes are connected to both hubs.

1. 22
2. 40
3. 80
4. 84

    

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[KarstenI]

Spoiler

Number of Hubs * (Number of Hubs -1)/2  * (Uplinks per Hub)^2 + Number of Hubs * Number of Spokes * Number of Uplinks on Hub * Number of Uplinks on Spoke

[RomanMD]

The question is quite interesting, but there is still at least one unknown variable...

So, this is why I don't like Cisco way of building questions.. 😞

[KarstenI]

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@RomanMD wrote:

The question is quite interesting, but there is still at least one unknown variable...

So, this is why I don't like Cisco way of building questions.. 😞

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Actually, there is no unknown variable in this question. Only one of the two options gives one of the offered answers.

[PhilipDAth]

Spoiler

Each spoke would have two tunnels to each hub, so 20 spokes*2 tunnels*2 hubs=80 tunnels.

The hubs would then have two tunnels between them for each Internet circuit.  So 2x2=4 tunnels.


So I'm going with 84 tunnels.

[UCcert]

D:84

[cmr]

E: 🐕

[Kamome]

Spoiler

Every spoke MX will establish 4 AutoVPN tunnels with Hub MXs. (Spoke MX have only 1 uplink, but every hub have 2 uplinks. So each hub will have 2 tunnels with each spoke. And there are 2 hubs, so every spoke will get 4 tunnels.)

There are 20 spoke MXs, so there will be total 80 tunnels, (4 tunnels per spoke x 20 spokes = 80 tunnels)

Plus, every hubs in same organization will create tunnels with every other hubs via all available uplinks. There are 2 hubs in this organization and every hub have 2 tunnels, so there will be 4 tunnels between hubs.

Therefore, total 84 tunnels will be created in this organization. (80 for Hub-Spoke, 4 for mesh between Hubs)

Ans) d. 84

[UCcert]

@cmr  😂 - Woof

[rbnielsen]

Honestly I'm more interested in the question regarding failover times. 😉

The Meraki Documentation is unclear on the point, and I have yet to meet someone with a convincing argument.

[GIdenJoe]

Thank god AutoVPN is not like regular IPsec VPN or you would need to count 1 phase 1 SA and 2 phase 2 SA's per individual tunnel, and even worse if you used policy based VPN with multiple traffic selectors...

But in this case before I looked at the spoilers I went for 84 too 😉

I know the questions omits the active active VPN option, but you need to select the "best" answer.

[RafaelM · Accepted solution]

Answer: d. 84

Explanation:

Every branch MX will form 2 tunnels to each hub (80 tunnels in total), and then the hubs will form 4 tunnels between each other (4 more tunnels), giving us a total of 84 tunnels!

I hope you have all enjoyed this practice question!

[wilanddar]

Are practice exams offered any where to test knowledge before the real thing