So what is a PvP plus or rapid pvp plus?
Extended bridge id now spanning tree requires that every switch have a unique bridge ID.
In the past there's simply consisted of the bridge priority and Mac address.
So bridge ID consists of eight bytes with two bytes being the bridge priority and six points being the
MAC address.
However, when configuring multiple VLANs and running per VLAN spanning tree, a different Mac address
would have to be allocated for every VLAN PVS.
RT creates an instance on a per VLAN basis.
So to ensure that the bridge ID is unique on a per VLAN basis, a different MAC address would have to
be allocated.
Now that works fine if you only have a few VLANs, but if you configuring hundreds or thousands of VLANs,
it's not scalable.
If a vendor was supporting PVS, DT, the vendor would need to assign a unique Mac address on a per
VLAN basis.
So in theory, if 4094 VLANs were supported on a switch, 4094 unique Mac addresses would need to be
assigned to every switch.
That's simply not scalable.
So to conserve Mac addresses, the system was changed and an extended system ID is also known as MAC
address reduction.
So with extended bridge IDs, the bridge ID is still eight bytes in size, but the priority is now split
into two parts.
So the two byte priority portion consists of a four bit bridge priority and a 12 but extended system
ID.
The MAC address is still six bytes in size.
So please note bridge priority is for bits.
Extended system ID is 12 bits, which equates to two bytes.
The extended system ID is populated with the VLAN number and the bridge priority is a value that you
can set.
Default is 32768 in decimal.
In the past the bridge priority consisted of two bytes and you could set the priority to a value such
as one.
However, that's no longer supported on a switch.
As an example, if I type spanning tree VLAN one priority and try and set it to one, I'm told that
I need to set it in increments of 4096 so the values allowed are one of these.
The reason for that is that the bridge property has been split into two portions with only the most
significant four bits being available for the priority.
So if you set the bridge priority portion the four bits to binary one and you take the full two bytes
into account, that would equate to 4096 in decimal.
So if the priority bit is set to one, the extended bridge ID priority works out to 4096.
If you take into account the full two bytes, if you set the bridge priority portion to two, so 0010
in binary and look at the full 16 bits or two bytes, it equates to 8192 in decimal.
On some vendor's equipment, you can set the priority to one and it will automatically be converted
to 8192.
But on Cisco switches, you need to set the bridge priority in multiples of 4096.
So once again, if I try and set the priority to one, it's not allowed.
Set it to 4000 and.
96.
That's allowed to show spanning tree.
Notice the property of the switch because it's running PV plus it's 4097.
So the priority plus the VLAN number, if you were looking at VLAN ten as an example, the priority
would be 4096 plus ten.
If you're looking at VLAN 20, it would be 4096 plus 20.
I'll demonstrate that in a separate video.
Now over the years, various enhancements have been made to spanning tree to reduce convergence time.
So in a switched environment, various enhancements have been made to the protocol to make sure that
things happen quicker.
A standard port on a switch could take 30 seconds to converge, and that's not acceptable in modern
day networks.
As an example, if the PC was booting up and needed to connect to a DHCP server, the PC would boot
up and send out a DHCP request before the switch port is converged.
So the PC would have already booted up and requested an IP address before 30 seconds have expired and
hence the PC wouldn't receive an IP address from the DHCP server because the DHCP request from the PC
would be dropped by this port which is blocking while it's converging.
So to improve performance in switched environments.
Edge ports, in other words, ports connected to edge devices such as PCs, some servers and routers
would be configured as Port First ports in a Cisco environment or as edge ports on other vendor equipment.
Cisco used the term port first.
Other vendors use the term edge ports.
In some terminology, Cisco will use the term port first, and in other terminology it will be referred
to as an edge port.
Now it's important that you only enable port first ports on access ports and not on trunk ports.
In other words, you shouldn't enable port first on links between switches because that will introduce
loops in your topology.
An edge port or a port first port immediately transitions to the forwarding state, so it bypasses the
listening and learning states.
It goes directly from blocking to forwarding, once again skipping both listening and learning states.
That allows for much quicker convergence because rather than waiting for spelling tree to go through
various stages such as blocking, listening, learning, forwarding the port just starts immediately
forwarding traffic and hence convergence is a lot quicker.
Spending trees still running on that port, but transitions immediately to forwarding.
So if for some reason a BPD view was received on the port, the port can go back to the blocking state.
It's good practice to do this because you don't want to inadvertently introduce loops because someone
plugged in a switch as an example by mistake on a port first port.