One of the big issues when you're setting up VLANs is that you have literally taken one big network
and separated it into two separate broadcast domains.
Now that's good because from security reasons and such we like that.
But the downside is is there sometimes you want these two separate networks to be able to talk to each
other. And you can but it can be a little bit messy.
So let's take a look over here.
So just to keep things simple what I'm going to say is I've said that this entire switch to be on
VLAN 2 and this switch underneath it to be on VLAN 3.
Of course we don't have to do it that way we could have ports on two and three all over the place.
But just for simplicity's sake we're going to say it's that way.
Now what I've done is I've thrown an old router on top of the two switches and I'm going to show you
how we used to do things in the old days.
If I've got two separate VLANs I'm going to have to use a router to interconnect them.
So I'm going to go something like this on on this particular router it has two ethernet ports. The other
ports are just used for management.
So I'm going to plug this puppy up
and it's going to look something like this.
So what I've done is I've taken one arbitrary port from VLAN 2 and plugged that into one side of my
router and then I took another arbitrary port from VLAN 3 and plugged it into the other side.
Now that I've got this all plugged in I can go into my router configuration and I can set it all up
and put in firewalls and Access Control list whatever I want to do to keep one VLAN from getting too far
into the other VLANs. So whatever I want to do there I can do.
The downside to this is that unless we come up with something different every time I come up with another
VLAN, that's going to be a separate broadcast domain.
And I'm going to have to keep adding more and more routers or at least adding more and more ports to
a single router to allow everybody to interconnect.
It's a mess.
So what we do instead is we use something called InterVLAN Routing.
Now InterVLAN Routing is in essence a virtualization of the functions of a router that's put into
higher end switches. With interVLAN routing turned on
I can say: OK I've got two VLANs: VLAN 2 and VLAN 3. And you literally go into your switch
configuration to do this.
So I go in I have VLAN two and VLAN three and I allow interVLAN routing and I turn it on and on a really good switch
I can even add things like access control and stuff like that.
So interVLAN routing is simply the tool that we use that if you make a bunch of VLANs and you're
going to have to reconnect them via routers instead of having a bunch of big ugly routers like this
laying around with the right type of switch and a little bit of patience, because sometimes interVLAN routing
can be challenging,
you can do it all within one or two boxes.