How to view root path cost (STP)

tomset

Anyone know how to see the "root path cost" of a switchport?

The "show spanning-tree vlan x" command only shows the path cost to the switch directly connected to it.

For instance, if a switch has 2 links to the root bridge each taking different routes to the root bridge, how can I see the difference in the root path cost between those 2 links?

MACattack

Okay for your question, I created 2 switch with 2 connection on both side

SW1 have to conenction to SW2

What I did is I created a trunk ports on both side and assigne SW1 as VTP server with domain CISCO and VTP client as SW2 with same domain.


SW1 with sh span root
SW1#show spanning-tree root
VLAN1
Root ID Priority 32768
Address cc01.0b54.0000
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
VLAN2
Root ID Priority 8192
Address cc01.0b54.0001
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
VLAN3
Root ID Priority 32768
Address cc01.0b54.0002
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

For client
SW2#show spanning-tree root
VLAN1
Root ID Priority 32768
Address cc01.0b54.0000
Cost 19
Port 2 (FastEthernet0/1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
VLAN2
Root ID Priority 8192
Address cc01.0b54.0001
Cost 19
Port 2 (FastEthernet0/1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
VLAN3
Root ID Priority 32768
Address cc01.0b54.0002
Cost 19
Port 2 (FastEthernet0/1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

As you can see VLAN 2 root bridge is SW1.

Then I assign SW2 as root for vlan 3


SW2#show spanning-tree root
VLAN1
Root ID Priority 32768
Address cc01.0b54.0000
Cost 19
Port 2 (FastEthernet0/1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
VLAN2
Root ID Priority 8192
Address cc01.0b54.0001
Cost 19
Port 2 (FastEthernet0/1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
VLAN3
Root ID Priority 8192
Address cc02.0b54.0002
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec


Now to get the path cost you need to manually check each switch trunks and run the command sw spa root. You need to DIG to be able to get the root path cost going to the root bridge.

marlon23

shutdown one of the links and see the new root path cost

MACattack

Or you can use
SW1#SHOW SPanning-tree BRIEF

VLAN1
Spanning tree enabled protocol ieee
Root ID Priority 32768
Address cc01.0b54.0000
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32768
Address cc01.0b54.0000
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 0

Interface Designated
Name Port ID Prio Cost Sts Cost Bridge ID Port ID

---

---

----

---

---

---

---

---

FastEthernet0/1 128.2 128 19 FWD 0 32768 cc01.0b54.0000 128.2
FastEthernet0/10 128.11 128 19 FWD 0 32768 cc01.0b54.0000 128.11

tomset

MACattack wrote:

Or you can use
SW1#SHOW SPanning-tree BRIEF

VLAN1
Spanning tree enabled protocol ieee
Root ID Priority 32768
Address cc01.0b54.0000
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32768
Address cc01.0b54.0000
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 0

Interface Designated
Name Port ID Prio Cost Sts Cost Bridge ID Port ID

---

---

----

---

---

---

---

---

FastEthernet0/1 128.2 128 19 FWD 0 32768 cc01.0b54.0000 128.2
FastEthernet0/10 128.11 128 19 FWD 0 32768 cc01.0b54.0000 128.11

I'll try this command out on my lab. From what you posted, it's only showing a cost of 19 which could just be the port cost and not the root path cost.