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Physical segment
If you are making a link to the "physical layer" you may be logic, but Cisco
uses the term "physical segment" here in a pretty misleading way.
As a
matter of fact you can very well have two different IP-networks on the same
switch/hub. So physically (and -if you want- data-link-wise) they
might theoretically communicate with each other.
But not logically (IP-wise),
since IP does not allow hosts of different IP-networks to communicate directly
with each other without the help of a router. But if they are on different
IP-networks but on the same switch, they definitely could see each others
broadcast.
So here a description of what Cisco has defined as "physical segment"
(for whatever reasons ...):
- A Broadcast Domain
The portion of the network that you can reach by
using a broadcast packet
- Ignore repeaters, bridges, or switches, they do forward broadcasts
- Everything (including all devices) between router ports, because routers
don’t forward broadcasts
- IP Addressing Rules:
All devices on the same physical segment share a
common network ID
A physical segment has a unique network IDs
Internetwork
a collection of individual networks, connected by intermediate networking
devices (bridge, hub, switch, router), that functions as a single large
network.
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