In a previous video we made switch one the spanning tree root for veal and ten and a veal and one as
well as making switch to the spending tree root for veal and 20 we can see that as an example by going
on to such one and topping shows spanning tree veal and 10 notice of this switch or this bridge is the
spanning tree root for Valentin as well as the spanning tree root for villain 1 yes which 2 so shows
spanning tree v land 20 the switch or bridge is the root for veal and 20.
Once again the reason why we use terms bridge rather than switch in spanning tree is that spanning tree
has been around for a long time.
So we talk about bridges rather than such as in some of the spanning tree terminology spanning tree
was developed when bridges were used instead of switches.
So we've got the roots configured in spanning tree.
We have enabled in previous videos redundancy between the switches.
So as an example switch three has to uplinks to the core.
And so to switch for so we have redundancy at layer 1 and layer 2.
But now we need to implement redundancy at layer three.
Here's the problem rudder one which is acting as P.S. One and this topology is in VLAN 10.
It needs to be configured with a default gateway so which switch will become its default gateway switch
one will switch to both switches have IP addresses in VLAN 10 switch one is tendered once attended one
and switch to is tendered Wanda tended to switch switch will be configured as the default gateway and
what will happen when that switch goes down as an example you probably want to make a switch one the
default gateway for router one because switch one is the spending tree route which should mean that
traffic at both layer 2 and layer 3 would traverse this link and get to switch one.
The problem is if you make switch one the default gateway for pieces in VLAN 10 and switch one goes
down where will those pieces send their traffic they won't be able to reach their default gateway which
means that they won't be able to send traffic off VLAN 10.
In other words they won't be able to access the Internet or other servers and devices in a separate
VLAN the same is true for devices in VLAN 20 if you lend twenty devices have switched to as the default
gateway in other words we configure the default gateways tendered one to twenty to two and switch two
goes down what happens then the default gateway is down which means that they won't be able to for example
ping devices in VLAN 10 or access devices on the Internet.
So this is where first hop redundancy protocols such as hot standby writing protocol or H.S. IP are
used it just IP is a Cisco proprietary protocol that allows you to implement first top redundancy the
industry standard version of the protocol is VR IP or virtual rudder redundancy protocol.
The idea here is that you configure your two switches with a virtual IP address these two switches will
have an election and choose who is in charge of forwarding traffic on behalf of a virtual router in
this topology will have two physical switches configured with IP addresses in say VLAN 10 but a virtual
switch or a virtual rudder is created through the configuration and that of virtual Rada or virtual
switch becomes the default gateway for your devices.
I'll talk about virtual Rodders rather than virtual switches or layer three switches for most of this
discussion because that's how HSR appears written and described but essentially what you do on your
P.C. is you configure a default gateway of a virtual switch
logically a Rada is created through H.S. or P..
Now this Rada is not a physical Rada or a real Rada that's going to exist in our topology.
It's simply created through the H.S. or P commands configured on the switches pieces such as the piece
in VLAN 10 will be configured with a default gateway.
In our example of ten dot 0 2 5 4 so rather than the PCI being configured with a default gateway of
switch one or switch to the default gateway.
Is this a virtual HS or piranha.
This I just hope he rather will have its own IP address as shown here for VLAN 10 will also configure
a another virtual router for VLAN 20.
In addition this Rada has its own Mac address based on a group number configured in HS or P.
The pieces are unaware that they are talking to a virtual device.
They think they are talking to a physical Rada but in actual fact they are talking to the switches which
are pretending to be this virtual Rada we can manipulate which physical switch is going to be forwarding
traffic on behalf of the virtual Rada by changing a priority the default priority in HS IP is 100 and
the highest priority ones so we'll influence H.S. IP so that switch 1 becomes what is called the active
router for VLAN 10 and switch to will be the standby router for VLAN 20 switch 2 will be the active
router and switch one will be the stand by Rada.
And that's because which one is the route in spanning tree for VLAN 10 and switch to is the route in
spanning tree for VLAN 20.
We want to ensure that traffic from this host and VLAN 20 is forwarded to its default gateway here which
is the same device that suspending tree root.
In other words traffic will take this path rather than the traffic having to go across multiple links
to get to the default gateway by the same token the switch will be the active router or active forward.
For VLAN 10 so that VLAN 10 traffic uses this uplink to get to the spending tree route as well as the
default gateway.