Uplinkfast and backbone fast for SWITCH

Cat5

I've been watching the CBT Nuggets for SWITCH, and as I've been going through them I thought I would see some on uplinkfast and backbonefast, but no. I thought they were concepts covered under the heading of STP? It covers this, as well as RSPT, but I also don't see him talking much about PVST, either. I'm curious why.

lrb

When they talk about STP with respect to IOS/NX-OS, they will be implicitly referring to PVST unless they specifically mention CST (one STP instance for all VLANs). Other vendors can and do use different terms when referring to single-instance, multi-instance, and per-VLAN spanning tree (Junos refers to PVST as VSTP for example)

Unfortunately until the CCNP gets refreshed, the topics on the blueprint for the three exams will remain vague and broad. If you look at the newer versions of the CCNA and CCIE you will see that the topics on the blueprint are very specific. UplinkFast and BackboneFast is covered under SWITCH blueprint sections 1.4 and 1.5 probably. If the CBT nuggets videos don't explain the concepts, just google the theory and configuration of them as they aren't too difficult.

fredrikjj

Cat5 wrote: »

I'm curious why.

Because a CBT Nuggets video series doesn't cover all protocol features? Alternatively, because in the grand scheme of things, legacy Cisco enhancements to a STP version that no one should be using anymore aren't super important.

Cat5

fredrikjj wrote: »

Alternatively, because in the grand scheme of things, legacy Cisco enhancements to a STP version that no one should be using anymore aren't super important.

I would agree with the uplinkfast and backbonefast, but not the portfast. It seems to be in use quite a bit.

I understand that uplinkfast and backbonefast aren't used in RSTP, but they are used with classic STP. Is PVST+ only used in classic STP and not in RSTP, in both, or what?

fredrikjj

I didn't see portfast in your post, but yeah, that's an important feature. Technically, I think that portfast is an "edge port" in 802.1w but Cisco maintains the terminology from the old version. Don't quote me on that though.

Rapid Spanning Tree Protocol is a standard called 802.1w. Cisco doesn't support plain 802.1w, only Rapid-PVST and MST which are based on 802.1w but has additional functionality. You could run MST with 1 instance for all vlans to essentially get the same functionality as 802.1w.

fredrikjj

PS.
I would recommend that you simply start out with learning plain old PVST+, ignoring the enhancements. Once you have that down, gradually add the enhancements one by one. Then learn Rapid-PVST and MST. Despite being ancient, PVST+ is the focus of the exam if you look at the official textbooks. Presumably, the idea is that it will be easier to understand the newer versions if you have a solid base in 802.1d

instant000

802.1w I remember the good ol' "w" for "wapid spanning tree".

I guess it was an effective learning aid, because I still remember it.

ande0255

I like that wapid spanning tree idea, thank you for that!

Cat5

It's the goofy mnemonic tricks that stick the best. That's a good one.

roberthock

In Jeremy's 3rd video on spanning-tree, the RSPT PVST+ video, he does go over portfast in depth. He actually demonstrates unplugging the link from the pc multiple times to show how fast it is. He also briefly mentions uplink fast and backbone fast, but only to mention they are legacy. If you want more information on those and MST, CST, ect. the official cert guide covers them in the spanning-tree chapters.

Hope this helps!

P.S. - I am also studying for switch too.

tomtom1

fredrikjj wrote: »

I didn't see portfast in your post, but yeah, that's an important feature. Technically, I think that portfast is an "edge port" in 802.1w but Cisco maintains the terminology from the old version. Don't quote me on that though.

Yes, you are correct as far as I understand. In RSTP (802.1w) an edge port is considered a port where portfast is enabled. See this example

SW02#sh spanning | i rstp
  Spanning tree enabled protocol rstp


SW02#sh run int fa0/20
Building configuration...


Current configuration : 85 bytes
!
interface FastEthernet0/20
 switchport access vlan 50
 switchport mode access
end


SW02#sh spanning vlan 50 | i Fa0/20
Fa0/20              Desg FWD 3019      128.22   P2p 

As you can see we have a simple access port in VLAN 50 on a switch running RSTP. Portfast is currently not enabled on this switch. When we enable portfast on the switchport (spanning portfast) the port type changes from P2p (Point to Point) to P2p Edge:

SW02#sh spanning vlan 50 | i Fa0/20
Fa0/20              Desg FWD 3019      128.22   P2p Edge 

SW02#sh run int fa0/20 | i portfast
 spanning-tree portfast

Danielh22185

Correct me if I am wrong but when using RPVST an edge port already behaves as if it was configured with port fast from traditional spanning tree. So long as the port is configured as switchport mode access within RPVST mode.

tomtom1

Danielh22185 wrote: »

Correct me if I am wrong but when using RPVST an edge port already behaves as if it was configured with port fast from traditional spanning tree. So long as the port is configured as switchport mode access within RPVST mode.

Yes, that is correct, but Cisco's implementation still requires the use of the portfast command.

Edge Ports


The edge port concept is already well known to Cisco spanning tree users, as it basically corresponds to the PortFast feature. All ports directly connected to end stations cannot create bridging loops in the network. Therefore, the edge port directly transitions to the forwarding state, and skips the listening and learning stages. Neither edge ports or PortFast enabled ports generate topology changes when the link toggles. An edge port that receives a BPDU immediately loses edge port status and becomes a normal spanning tree port. At this point, there is a user-configured value and an operational value for the edge port state. The Cisco implementation maintains that the PortFast keyword be used for edge port configuration. This makes the transition to RSTP simpler.

Source: Understanding Rapid Spanning Tree Protocol (802.1w) - Cisco

SW02#sh run | i spanning-tree mode
spanning-tree mode rapid-pvst


SW02#sh run int fa0/12
Building configuration...


Current configuration : 58 bytes
!
interface FastEthernet0/12
 switchport mode access
end

SW02(config)#int fa0/12
SW02(config-if)#spanning portfast

When I enable portfast and do the test the link is able to go from BLK to FWD without the forward delay.

SW02#sh spanning int fa0/12


Vlan                Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
VLAN0001            Desg FWD 19        128.14   P2p Edge 

Also notice the edge statement here.