Tag Archive Rapid PVST Traffic Engineering details

Implementing Rapid PVST Traffic Engineering on Cisco Nexus Switches

NX-OS runs Rapid Per-VLAN Spanning-Tree Protocol by default. This means that for each VLAN that is created, a separate instance of STP is created, with each of these running the 802.1w RSTP algorithm. Beyond this, the default behavior of STP on NX-OS is essentially identical to that of Catalyst IOS.

Platform: https://racks.uninets.com

Lab Name: Nexus 9k NXOSv

Access full Cisco Nexus lab guide here:  https://bit.ly/2ZgF36G

Task

• Erase the previous configuration on switches NXOS01, NXOS02, NXOS03 and NXOS04 using command “write erase” and reload both switches, assign hostname the same hostname to both switches. Use provisioning documents if required
• Configure all links connecting NXOS01, NXOS02, NXOS03, and NXOS04 as 802.1Q trunk ports.
• Configure the links connecting NXOS03 and NXOS04 as a port channel 1.
• Create VLANs 10 and 20 on all switches, and assign them as follows:
  • Win Server’slink to NXOS03 should be in VLAN 10 and use the IP address 10.0.0.1/24.
  • Win Server’slink to NXOS04 should be in VLAN 20 and use the IP address 20.0.0.1/24.
  • SW’s link to NXOS03 should be in VLAN 20 and use the IP address 20.0.0.2/24.
  • SW’s link to NXOS04 should be in VLAN 10 and use the IP address 10.0.0.2/24.
• Configure Spanning-Tree Protocol between the switches as follows:
  • All switches should use 32 bits for spanning-tree port path costs.
  • NXOS01 should be the STP Root Bridge for VLAN 10, with NXOS02 being the backup Root Bridge.
  • NXOS04 should be the STP Root Bridge for VLAN 20, with NXOS03 being the backup Root Bridge.
  • Win Server’sVLAN 10 traffic to SW should follow the path of NXOS03 ->NXOS02 ->NXOS01 ->NXOS04 ->SW.
  • SW’s VLAN 20 traffic to Win Server should follow the path of NXOS03 ->NXOS01 ->NXOS02 ->NXOS04 -> Server 1.
• Keep saving your configuration using command “copy run start”

Configuration

NXOS03:

NXOS04:

NXOS01:

NXOS02:

SW:

Verification

 Assign IP addresses to WinServer on its both interfaces

Notice the Mac address of both the interfaces on WinServer interfaces. Marked in yellow.

Notice the Mac addresses on SW interfaces

Verification of this task can be performed by viewing the Root Bridge and Root Port election on a per-switch basis, or by viewing the MAC address table, as the STP topology ultimately controls which interfaces can participate in MAC address learning. Below we see that for VLAN 10, NXOS01 is elected the Root Bridge. This implies that all of its VLAN 10 links will be Designated ports in the Forwarding state.

Try to send PING traffic from SW to WinServer or vice versa. In case traffic dies out, use continuous ping to generate traffic.

MAC addresses for VLAN 10 are being learned in ports Eth2/5 and Eth1/1, which implies that NXOS04 and NXOS02 on the other end of these links, respectively, have chosen those ports as their Root Ports.

Use command “show mac address-table dynamic vlan 10” on physical switch which represents the same output.

Per the output below, NXOS02 chose E1/1 as the Root Port to reach NXOS01. Although all ports have the same cost of 2000, E1/1 has the lowest Port ID (port priority and port number) on the other end of the link.

Per the view of the CAM table below, we see that NXOS02 learns MAC addresses for VLAN 10 in Eth1/1, its root port, and Eth2/5, the downstream link connecting to NXOS03.

Look on for mac addresses in VLAN 10

Use command “show mac address-table dynamic vlan 10” on physical switch which represents the same output.

On the next downstream switch, NXOS03, we see that it has chosen Eth1/8, a link to NXOS02, as its Root Port. This is because other possible paths to the Root Bridge have had their cost raised to 99999. The end result is that traffic received from Win Serverin VLAN 10 going to SW is first forwarded to NXOS02, then to NXOS01, then to NXOS04, and finally to SW.

Note: Use command “show mac address-table dynamic vlan 10” on physical switch which represents the same output.

Likewise, traffic in VLAN 20 from SW can be verified to follow the path of NXOS03 ->NXOS01 ->NXOS02 ->NXOS04 ->Win Serverby the CAM tables below.

Look only for mac addresses in VLAN 20