In this topology, if PC 1 sends a broadcast where will it go? So what will happen if we put this PC into
a separate VLAN will broadcast be forwarded out of this port and this port?
Switch 1 has no configuration at the moment.
So show MAC address table we can see that a source MAC address was learnt on gigabit 01 and
this MAC address was learnt on gigabit 00.
In other words the switch to back to the router as well as the ostinato device sending synthetic or
generated frames. Show VLAN brief at the moment we only have the default VLANs gigabit 01 belongs
to VLAN 1.
So I'll create VLAN 2 and then go on to gigabit 01 and type switch port access VLAN 2 to put
that port into VLAN 2, so show interface gigabit 01 switch port
this port is now in the VLAN 2.
We have moved the PC into a separate VLAN.
So what I'll do is stop Ostinato and then start it again.
So we're still generating frames
these are broadcast frames that are being generated.
Do we see any traffic on that interface? No broadcasts are being received on this interface.
What about this interface?
Again no broadcasts from the PC are being received even though the PC is sending the broadcasts
because the switch has been configured with VLANs broadcasts received on this interface are not forwarded
out of gigabit 02 or 00 because they are in separate VLANs.
But if we configured gigabit 00 as a trunk so we use the command switch port trunk encapsulation dot
1q switch port mode trunk.
What would happen now? Would broadcast be forwarded on that port?
So show interface gigabit 00 switch port it's configured for trunking.
It's operating as a trunk.
We can see that by typing show interface trunk.
So gigabit 00 has been manually configured as a trunk, will broadcast before it across that port?
So this is the Wireshark capture on gigabit 00 from the switch to gigabit 00 on the router
and as you can see broadcast frames are being sent they are being put in to VALN 2.
In other words they are tagged with 82 dot1q tag 2 because the traffic was sent on a port
in VLAN 2.
So this port is an access port in VLAN 2 and this is a trunk port.
So on the trunk port they are tagged with VLAN 2 but broadcasts are being forwarded to the router.
The router however will not forward those broadcasts on.
So even if we configured the router as a router on the stick it would still not forward the frames.
So at the moment gigabit 00 is configured with an IP address but even if we did the following and
type encapsulation dot1q and specify VLAN 2
broadcast would not be received by the router but the router would not forward them on even if we configured
an IP address of let's say 10 120 254 on that interface because routers don't forward broadcasts
by default.
So I've got this IP address configured on gigabit 00.2 but if we do a capture on this interface
what you'll notice is no broadcasts are being forwarded on because routers block broadcasts by default.
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