Single vs dual-homed - so confused...

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Hey ITPro! I just finished the "Describe WAN Topology Options" show from the CCNA Route/switch 2018 track. I have to say, that piece on Single vs dual homed topologies confused the heck out of me. could you take a peek at this screenshot from the class, I added a question. Any chance there is a typo somewhere in the snip from the show notes or the example?

@Adam-Tyler,

The idea here is that on "our" side, there is a single device (single-homed), R1 in this instance. The "dual" connection (2 links). So the key here is the single-homed is answered in a question regarding the marked diagram above: Where is your SINGLE point of Failure in either scenario.

This single home can use dual links to a single ISP. This single point of failure would still be R1.

or

It can be the single router to 2 ISP with 2 links each. The single point of failure would still be R1.

Compare this to the other diagrams. Note multi-points of failures (multi-homed) must happen to take it down.

Hope this helps.

Thanks Ronnie, So "dual homed" means more than one customer router?

If that is true, from my screenshot of the course you'll notice the text"
dual-homed: dual connection to ISP
----dual-multihomed: single router with 2 connections to each different ISP.

Why is this example of a single router listed under dual-homed?

Regards,
Adam Tyler

@Adam-Tyler,

I think I didn't set the proper context in the diagram.

So this is probably has something to do with my poor explanation in the videos.

The diagram on the left is still considered dual-homed as a example because there are two possibilities of single points of failure: Either a link failure or a router failure in my example.

Though the router in this instance is a single point of failure. Here I was supposed to have elaborated on the fact that we eliminate every other single point of failure by adding multiple links and multiple ISPs.

So My first response was just looking at the router situation...not comparing to the upper right hand diagram where if you note-- we have multiple routers and multiple links but it is the router that will be the single point of failure on either ISP side or Enterprise side.

So I found a good article online that was able to dumb this down to my level pretty well. The notes I took are as follows...

Single homed, one connection to one ISP.
Dual homed, two connections to one ISP. ISP can have multiple routers and enterprise can have multiple routers. Or not.. Still considered dual homed

Single Multihomed, one connection each to two ISPs.
Dual Multihomed, two connections each to two ISPs.

Multihomed means two ISPs.

-Adam