1

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The problems asks if the first and fourth host are in the same subnet for the first picture. However, it seems quite different from pictures what I typically have seen (picture 2). So I conjectured that this is a combination of bus and star topology, so both hosts are in the same subnet.

But it seems strange a bit because I heard that bus toplogy is old-fashioned topology and star+switch topology replaced it so I can not understand why both bus and switches are used in the first picture.

Are two pictures are same? Is the first picture just ambiguous?

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I would have said they weren't so much ambiguous as badly drawn.

As you say, there are very few bus-topology wired ethernet networks these days. The main issue (with both diagrams) is that it looks like two connections go into one socket (eg the bottoms of the router and switches). I'm sure even these days you can get switches with 10base5 or 10base2 or AUI connectors, but I've never seen one. In the 1990s we used to use hubs with 16 port of 10baseT and one 10base2 BNC socket, and occasionally we used the BNC socket, such as during a transition to 10baseT.

On the assumption it's just a drawing issue ...

If you're drawing a diagram which needs to emphasise cabling, such as a patch diagram or physical layout, you might draw it more clearly like this:

More usually we hide the layer 2 detail of switches and draw something like this, where a given broadcast domain is conflated just into a fat line:

Hope that's helpful.

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