Month: August 2011

Cisco Nexus 5596’s with Redundant Uplinks to Catalyst 6509 Core’s Using vPC

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I recently had the opportunity to deploy a Cisco Nexus solution 5596UP switches for a healthcare customer. The Nexus switches represent Cisco’s presence in the Converged Fabric segment, which is gaining momentum recently as more IT shops seek to streamline datacenter infrastructure towards a “private cloud” approach. The Nexus 5000 series is primarily aimed at the edge, with Layer 3 capabilities available as an add-on.

The Nexus switches support vPC (Virtual Port Channels), which “allows links that are physically connected to two different Cisco Nexus 5000 Series switches or Cisco Nexus 2000 Series Fabric Extenders to appear as a single port channel by a third device.” (Cisco)

Here is a diagram of the planned configuration of vPC uplinks between the Nexus 5596UP and Catalyst 6509 (core) switches:


To setup vPC on the Nexus switches, first you need to create a vPC peer-link between the pair of Nexus switches. The peer-link must include at least 2 interfaces.

feature vpc
vpc domain 1
  role priority 4096
  system-priority 2000
  peer-keepalive destination 192.168.100.20
  auto-recovery

interface port-channel20
  switchport mode trunk
  vpc peer-link
  switchport trunk allowed vlan 100,103-104,901
  spanning-tree port type network

interface Ethernet1/23
  description Link 1 to 5596-sw2
  switchport mode trunk
  switchport trunk allowed vlan 100,103-104,901
  channel-group 20 mode active

interface Ethernet1/24
  description Link 2 to 5596-sw2
  switchport mode trunk
  switchport trunk allowed vlan 100,103-104,901
  channel-group 20 mode active

Repeat on the 2nd Nexus switch.

Next you need to create the virtual port-channels on the Nexus side. We will create one port-channel per uplink interface.

interface port-channel1
  switchport mode trunk
  vpc 1
  switchport trunk allowed vlan 100,103-104,901

interface port-channel2
  switchport mode trunk
  vpc 2
  switchport trunk allowed vlan 100,103-104,901

interface Ethernet1/1
  description uplink to Core1-7/8
  switchport mode trunk
  switchport trunk allowed vlan 100,103-104,901
  spanning-tree guard loop
  channel-group 1 mode active

interface Ethernet1/2
  description uplink to Core2-6/7
  switchport mode trunk
  switchport trunk allowed vlan 100,103-104,901
  spanning-tree guard loop
  channel-group 2 mode active

Again, repeat for the 2nd Nexus switch.

Notice that spanning-tree Loop Guard has been enabled on the uplinks to prevent STP looping issues. Also, the Allowed VLAN’s should match the VLAN ID’s allowed in the peer-link.

Finally, create the port channels on the Catalyst side. Here we will create ONE port channel per Catalyst, consisting of the uplinks from each Nexus switch, so that the Catalyst will see the Nexus pair as a single switch. Until this step is complete, the vPC status will show as down.

interface Port-channel200
 description “Connection to Nexus”
 switchport
 switchport trunk encapsulation dot1q
 switchport mode trunk
 no ip address
 spanning-tree guard root

interface TenGigabitEthernet7/6
 description NEXUS SW2 PORT1
 switchport
 switchport trunk encapsulation dot1q
 switchport mode trunk
 no ip address
 spanning-tree guard root
 channel-group 200 mode active

interface TenGigabitEthernet7/8
 description NEXUS SW1 PORT1
 switchport
 switchport trunk encapsulation dot1q
 switchport mode trunk
 no ip address
 spanning-tree guard root
 channel-group 200 mode active

Repeat this process for the 2nd Catalyst switch.

Now the vPC status should show as up-

5596-sw1(config-if)# sh vpc
Legend:
                (*) – local vPC is down, forwarding via vPC peer-link

vPC domain id                   : 1   
Peer status                     : peer adjacency formed ok      
vPC keep-alive status           : peer is alive                 
Configuration consistency status: success
Per-vlan consistency status     : success                       
Type-2 consistency status       : success
vPC role                        : primary                       
Number of vPCs configured       : 2   
Peer Gateway                    : Disabled
Dual-active excluded VLANs      : –
Graceful Consistency Check      : Enabled

vPC Peer-link status
———————————————————————
id   Port   Status Active vlans    
—   —-   —— ————————————————–
1    Po20   up     1,100,103-104                                            

vPC status
—————————————————————————-
id     Port        Status Consistency Reason           Active vlans
—— ———– —— ———– ————————– ———–
1      Po1         up     success     success                   1,100,103-104         
2      Po2         up     success     success                  1,100,103-104    

Here
is a useful Cisco reference document on vPC for the Nexus 5000 series.

Notes:

  • This configuration only applies if there is NOT VSS established between the Catalyst 6509 core’s.
  • You can rely on Spanning Tree for establishing redundant links from a Nexus pair to dual Core’s, with only one uplink marked as active by STP. This customer insisted on getting the aggregated bandwidth from both 10Gb uplinks, as they planned to converge additional applications onto the Nexus in the future.
  •  If at all possible, you should test this configuration in a lab before production deployment. At a minimum, deploy these changes during a maintenance window as there is a risk of network outage mainly due to looping behavior – spanning-tree root guard, loop guard are strongly recommended!

Happy vPC’ing!