Administrator Guide

24 Dell Campus Networking Interoperability with Cisco Catalyst 1.1 | version 1.1
2.6 Spanning Tree Protocol (RSTP-PV and RPVST+)
In traditional STP and Rapid STP (802.1d and 802.1w respectively), layer 2 loops are prevented by placing
certain ports in blocking (STP) or discarding (RSTP) states. The overall effect of this is half of the available
Ethernet links leading back to the core of a network are not in use most of the time. By using a STP instance
per VLAN, a manual load balancing method can be achieved allowing overall better utilization of available
bandwidth in a network.
Rapid Per-VLAN Spanning Tree Plus (RPVST+) is a Cisco proprietary STP protocol available on the Cisco
6504. Dell Networking N-Series switches can work with RPVST+ through the use of Rapid Spanning Tree
Protocol per VLAN (RSTP-PV). RPVST+ and RSTP-PV allow a direct one-to-one mapping of STP instances
to VLANs. In Figure 9 below, VLANs 30 through 35 are configured on the three switches from the previous
configuration sections. Using RPVST+ and RSTP-PV, six STP instances are created to allow the VLANs to
be split evenly between the trunk ports connecting the Dell N-3024 switches to the Cisco 6504-E.
VLANS 30-35
VLANS 30-32
VLANS 33-35
1
2
3
FAN
STATUS
3
FAN-MOD-4HS
WS-C6504-E
STATUS
WS-X6748-GE-TX
47
48
37
38
35
36
25
26
23
24
13
14
11
12
1
2
4 8 P O R T
12
11
9
10
7 8 5 6 3 4 1 2
24
23
21 22 19 20 17 18 15 16 13 14 36
35
33 34 31 32 29 30 27 28 25 26 48
47
45 46 43 44 41 42 39 40 37 38
10/100/1000
GE MOD
FABRIC ENABLED
RJ45
SUPERVISOR 720 WITH INTEGRATED SWITCH FABRIC/PFC3
VS-S720-10G
STATUS SYSTEM ACTIVE PWR MGMT
RESET
DISK 0
1
LINK LINK
2
3
UPLINK
CONSOLE
LINK
10GE UPLINK
4 5
USB
LINK
EJECT
SFP
10/100/1000
STATUS
8 PORT 10 GIGABIT ETHERNET MODULE
WS-X6708-10GB
PORT
3
PORT
2
PORT
4
PORT
1
LINK LINK LINK LINK LINK LINK LINK LINK
PORT
5
PORT
6
PORT
7
PORT
8
Cisco 6504
Dell N3024-1
Dell N3024-2
27 29 31 33 35
28 30 32 34 36
37 39 41 43 45 47
38 40 42 44 46 48
LNK ACT
7 9 11
2 4 6 8 10 12
13 15 17 19 21 23
14 16 18 20 22 24
25
26
Stack No.
1
2
1 2SFP+
COMBO P
LNK ACT
5
27 29 31 33 35
28 30 32 34 36
37 39 41 43 45 47
38 40 42 44 46 48
LNK ACT
7 9 11
2 4 6 8 10 12
13 15 17 19 21 23
14 16 18 20 22 24
25
26
Stack No.
1
2
1 2SFP+
COMBO P
LNK ACT
5
Per-VLAN STP Diagram
2.6.1 Configuring Spanning Tree Protocol — Dell N-Series
The command spanning-tree mode rapid-pvst enables RSTP-PV and the command spanning-
tree vlan n-n priority 1 where n-n represents a VLAN ID range and a priority of 1 sets a priority
value to the VLAN range. This priority value is used to calculate the root bridge. Setting the priority to 1
guarantees the switch will be the root bridge for the respective VLAN STP topologies. The command show
spanning-tree summary confirms that RSTP-PV has been enabled. Finally, the command show