In this topology if PC 1 sends a broadcast way will it go?Assume that switch 1 and switch 2 or
with any VLANs except the default VLANs and draw that router 2 is configured with subnet 10 110 on
gigabit 00 and subnet 10 120 on gigabit 01.
In other words, the router has an IP address such as the following configured on gigabit 00 and an
IP address of the following configured on gigabit 01.
Where will traffic go if PC 1 sends a broadcast? What do you think? Ostinato order is a great little
application that allows us to generate network traffic.
So before I configure the PC to forward traffic what I'll do is configure the router with an IP address
on each interface. No configuration has been done on the switches,
so where will traffic go?
If PC 1 sends a broadcast so show IP interface brief on the router shows us that both interfaces are
up,
apart from that I've done no configuration. Here's the console for PC 1 so I'll startup Ostinato and
on the Ethernet interface I'm going to generate traffic.
Now I need to use Ethernet 1 rather than Ethernet 0 on these Ostinato devices.
So I'll re-cable the network
the principle however is the same.
All I'm doing is flipping the interface number on the Ostinato devices
but where will traffic go?
So I'll start a new stream generation
and I'll configure the PC to generate IP version 4 traffic that UDP traffic.
I'll configure the MAC address as all ones in other words it's a broadcast frame for the IP version 4
destination I'll set it to a broadcast as well.
So destination MAC address is all ones
In other words a broadcast, so IP version 4 destination is a broadcast.
So what I'll firstly do is start a capture between the switch and the router and I'll also do it on this side
and then I'll capture traffic between the switch on the left and Ostinato PC 2 as well as 3
and 4.
What I'll do in this case is send a thousand frames at one frame per second.
Click Apply and start sending frames on the Ethernet 1 interface the frames being sent have increased.
We've had about 10 frames sent now.
So on the link between the switch and the router.
So this is between IOS V layer 2 switch gigabit 00 and the router on gigabit 00.
We are seeing that broadcast traffic, what about on this link here?
So this is traffic between the router and switch 2 notice we don't see any UDP traffic.
The broadcast traffic is not being received on this link.
What about this link?
So this is the link between IOS V layer 1 gigabit port 02 to Ostinato device 2 filter for UDP traffic.
You can see the broadcast traffic being sent on that port so IP address and layer 2 address. So broadcast
traffic is being sent here.
What about on this link?
So this is the link between IOS switch 2 gigabit 01 and Ostinato 3.
No broadcast traffic is received there.
And what about switch 2 Gigabit 02 to Ostinato device 4 no UDP traffic is received there but
we are receiving it between the switch and the router and we are receiving it between the switch and
the second ostinato device.
So in other words a broadcast sent by this device is going to be flooded out of all ports on Alade to
switch except the port in which it arrived
but a router will block broadcast frames.
Modern routers by default do not forward broadcast frames.
So in this topology, we have what is called two broadcast domains.
The router is blocking broadcasts on this link so broadcasts are not forwarded.
Now, what happens if we put the PC into separate VLAN. I hope you enjoyed this video if it's been of benefit
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