Comments on: Host to Host Communication

By: Ed Harmoush

Ed Harmoush — Wed, 10 May 2023 18:20:26 +0000

In reply to smiley. > is it just a case of both ip addresses being within the same subnet defined by the netmask associated with the sending interface Yes, 100% =) The sending device is using their own IP/Subnet Mask to determine which target hosts are "within the network" and which are on "external networks".

By: smiley

smiley — Wed, 10 May 2023 08:42:27 +0000

Since there are no Routers in this illustration, we know all the communication is happening within the same network. Yes we do, but how is that known by the elements involved - is it just a case of both ip addresses being within the same subnet defined by the netmask associated with the sending interface? Though presumably that can get more complicated when two networks are bridged? I'm puzzled how this is resolved in general; ie given a destination ip, what determines if we query ARP for its mac address, or do a lookup in the routing table?

By: Ed Harmoush

Ed Harmoush — Fri, 04 Nov 2022 20:32:59 +0000

In reply to Bone. You're welcome =)

By: Bone

Bone — Sat, 29 Oct 2022 20:40:23 +0000

Great work sir.
Thank you very much.

By: Ed Harmoush

Ed Harmoush — Tue, 29 Mar 2022 17:20:43 +0000

In reply to Raveen. Glad you enjoyed it!

By: Raveen

Raveen — Sun, 27 Feb 2022 08:46:49 +0000

Explanation is really great

By: Daivid

Daivid — Wed, 21 Apr 2021 15:13:02 +0000

In reply to Ed Harmoush. Thank you very much for responding. I learn a lot from your articles. Amazing didactics.

By: Ed Harmoush

Ed Harmoush — Tue, 20 Apr 2021 19:57:25 +0000

In reply to Daivid. Yes, mostly. Home Routers are just simple L3 devices. But more and more the home routers come with additional features. Things like a UI you can log into and change settings or see who is connected, etc. Those elements would be considered "applications", meaning that particular home Router operates at layer 7. Remember, "Routing" is simply the function of moving packets between networks -- this is a purely Layer 3 task. A "Router" as we know it is a device who's primary purpose is Routing, but not it's only purpose. Some of those other purposes might require the Router to operate "above" Layer 3. Hope this helps.

By: Daivid

Daivid — Tue, 20 Apr 2021 19:50:34 +0000

In reply to Ed Harmoush.

Yes, I forgot to mention in the question that it is a Windows Server computer as a Gateway. In the case of a “Standard Gateway – Home Router” does it operate only at the network layer as you said correct?

By: Ed Harmoush

Ed Harmoush — Thu, 15 Apr 2021 17:37:03 +0000

In reply to Daivid.

You could say that, yes. But keep in mind the computer also can use TCP or UDP, and various network applications. So typically it’s considered that PC’s operate at all layers of the OSI model.

As for Gateways, it depends what you mean by it. If you mean application layer gateways, then yes, they operate on all layers. If you simply mean “gateway” as in “default gateway” i.e., nearest Router, then no, Routers operate up to Layer 3.

But keep in mind, these aren’t strict rules. See the end of this video for more details:

https://www.youtube.com/watch?v=0aGqGKrRE0g