PT LAB: Bringing up Nours small network – STP portfast & RSTP

This is how my small network looks so far:  https://me2learn.wordpress.com/2014/09/28/pt-lab-bringing-up-nours-small-network/

Spanning tree protocol has some cool feature for fast convergence, in this post I wish to configure and test them.

1- Port fast (Edge of the network)

access_1(config)#int range fa 0/1 – 2

access_1(config-if-range)#spanning-tree portfast

%Warning: portfast should only be enabled on ports connected to a single

host. Connecting hubs, concentrators, switches, bridges, etc… to this

interface when portfast is enabled, can cause temporary bridging loops.

Use with CAUTION

%Portfast will be configured in 3 interfaces due to the range command

but will only have effect when the interfaces are in a non-trunking mode.

I have configured the port fast feature in 2 hosts for one of my access layer switches, I will shut the PC’s off and see the difference in spanning tree ,,, and its working amazingly 🙂

access_1#show vlan

VLAN Name Status Ports

20 sales active Fa0/2, Fa0/3

Part of the output from (show spanning tree)

VLAN0020

————————-

Fa0/2 Desg FWD 19 128.2 P2p

Fa0/3 Desg FWD 19 128.3 P2p

Fa0/20 Root FWD 19 128.20 P2p

Now shut off both PCs – and bring them up immediately

%LINK-5-CHANGED: Interface FastEthernet0/2, changed state to down

%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/2, changed state to down

%LINK-5-CHANGED: Interface FastEthernet0/3, changed state to down

%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/3, changed state to down

Interface Role Sts Cost Prio.Nbr Type

—————- —- — ——— ——– ——————————–

Fa0/2 Desg FWD 19 128.2 P2p

Fa0/3 Desg LRN 19 128.3 P2p

Fa0/20 Root FWD 19 128.20 P2p

 

Interface Role Sts Cost Prio.Nbr Type

—————- —- — ——— ——– ——————————–

Fa0/2 Desg FWD 19 128.2 P2p

Fa0/3 Desg FWD 19 128.3 P2p

Fa0/20 Root FWD 19 128.20 P2p

 

-> Uplink and backbone fast aren’t supported in PT

 2- Rapid Spanning Tree (RSTP):

I want to check how fast the network is recovering using STP and then using RSTP. I will start a ping from PC in VLAN 20 to the GW and check distribution layer switch (dist_2)  then I am going to shut fa 0/23 the direct link to the core switch near my router (the root port)

dist_2#show spanning-tree vlan 20

Interface Role Sts Cost Prio.Nbr Type

—————- —- — ——— ——– ——————————–

Fa0/19 Altn BLK 19 128.19 P2p

Fa0/20 Desg FWD 19 128.20 P2p

Fa0/21 Desg FWD 19 128.21 P2p

Fa0/22 Desg FWD 19 128.22 P2p

Fa0/23 Root FWD 19 128.23 P2p

Fa0/24 Altn BLK 19 128.24 P2p

STP-shut-port

The same drop happened when I enabled fa 0/23 back

STP-enable-port

 

Now, let me move to the RSTP and see how it goes repeating the same steps

dist_2(config)#spanning-tree mode rapid-pvst

Interface Role Sts Cost Prio.Nbr Type

—————- —- — ——— ——– ——————————–

Fa0/19 Altn BLK 19 128.19 P2p

Fa0/20 Desg FWD 19 128.20 P2p

Fa0/21 Desg FWD 19 128.21 P2p

Fa0/22 Desg FWD 19 128.22 P2p

Fa0/23 Root FWD 19 128.23 P2p

Fa0/24 Altn BLK 19 128.24 P2p

 

dist_2#config t

dist_2(config)#int fa 0/23

dist_2(config-if)#shut

RSTP-shut-port

 

The ping didn’t drop when I enabled the port back – after having RSTP enabled for the whole network

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