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doublesided vPC set STP blocking portchannel and uses peerlink instead

moelka
Level 1
Level 1

Hi all,

I have the following doublesided vPC topology

 vPC-Example.jpgwfw

Say, vlan 10 traffic passes through NX9K3, instead of using the port channel, it goes through the vPC peerlink, and through NX9K4. STP is blocking the port channel, and designating the peerlink, which is an indication of a loop detection. Is it normal behavior, or did I just make a bad design or wrong configuration?

EDIT: Just to make it clear, NX9k1&2 are spines, and 3&4 are leaf switches, each pair have their own vpc domains. So, the spines provide vpc to the leafs, and leafs provide vpc to the clients. I'm thinking that if a client connected on NX9K3 with vlan 10, the traffick should go NX9K3 -> Spines, and not through NX9K3 -> NX9K4 -> Spines.  

Heres is the config for the 4 switches:

 

 

NX9K1# sh run vpc && sh run int po1 membership
feature vpc
vpc domain 10
role priority 20
peer-keepalive destination 10.0.0.2 source 10.0.0.1

interface port-channel1
  description vPC link - NX9K3
  switchport mode trunk
  mtu 9216
  vpc 1

interface Ethernet1/3
  description vPC link - NX9K3
  switchport mode trunk
  mtu 9216
  channel-group 1 mode active
  no shutdown

interface port-channel2
  description vPC link - NX9K4
  switchport mode trunk
  mtu 9216
  vpc 2

interface Ethernet1/4

  description vPC link - NX9K4
  switchport mode trunk
  mtu 9216
  channel-group 2 mode active
  no shutdown

 

 

 

 

NX9K2# sh run vpc && sh run int po1 membership
feature vpc
vpc domain 10
role priority 30
peer-keepalive destination 10.0.0.1 source 10.0.0.2

interface port-channel1
  description vPC link - NX9K3
  switchport mode trunk
  mtu 9216
  vpc 1

interface Ethernet1/3
  description vPC link - NX9K3
  switchport mode trunk
  mtu 9216
  channel-group 1 mode active
  no shutdown

interface port-channel2
  description vPC link - NX9K4
  switchport mode trunk
  mtu 9216
  vpc 2

interface Ethernet1/4

  description vPC link - NX9K4
  switchport mode trunk
  mtu 9216
  channel-group 2 mode active
  no shutdown
NX9K3# sh run vpc && sh run int po1 membership
feature vpc
vpc domain 20
role priority 20
peer-keepalive destination 10.0.1.2 source 10.0.1.1

interface port-channel53
  description Link - Spines
  switchport mode trunk
  mtu 9216

interface Ethernet1/53
  description Link - NX9K1
  switchport mode trunk
  mtu 9216
  channel-group 53 mode active
  no shutdown

interface Ethernet1/54
  description Link - NX9K2
  switchport mode trunk
  mtu 9216
  channel-group 53 mode active
  no shutdown
NX9K4# sh run vpc && sh run int po1 membership
feature vpc
vpc domain 20
role priority 300
peer-keepalive destination 10.0.1.1 source 10.0.1.2

interface port-channel53
  description Link - Spines
  switchport mode trunk
  mtu 9216

interface Ethernet1/53
  description Link - NX9K1
  switchport mode trunk
  mtu 9216
  channel-group 53 mode active
  no shutdown

interface Ethernet1/54
  description Link - NX9K2
  switchport mode trunk
  mtu 9216
  channel-group 53 mode active
  no shutdown

 

 

1 Accepted Solution

Accepted Solutions

Christopher Hart
Cisco Employee
Cisco Employee

Hello!

Typically in a double-sided vPC, both vPC domains have a single vPC running between them. In your scenario, you have two separate vPCs on each vPC peer, which is forcing Spanning Tree Protocol to block one of them.

An example might work best here. In your topology, NX9K1 has Ethernet1/3 in vPC Po1 towards NX9K3 and Ethernet1/4 in vPC Po2 towards NX9K4. NX9K2 has identical configuration. Typically, we could expect both Ethernet1/3 and Ethernet1/4 of both NX9K1 and NX9K2 to be placed in the same vPC (let's call it Po10, just to differentiate it from your existing vPC Po1 and vPC Po2). Similarly, Ethernet1/53 and Ethernet1/54 of NX9K3 and NX9K4 would be placed in the same vPC as well (we'll call this Po20, just to differentiate it from the new vPC Po10).

A rough, untested example of this configuration is below.

NX9K1# show running-config
<snip>
feature vpc vpc domain 10 role priority 20 peer-keepalive destination 10.0.0.2 source 10.0.0.1 interface port-channel10 description vPC link - NX9K3 and NX9K4 switchport mode trunk mtu 9216 vpc 10 interface Ethernet1/3 description vPC link - NX9K3 switchport mode trunk mtu 9216 channel-group 10 mode active no shutdown interface Ethernet1/4 description vPC link - NX9K4 switchport mode trunk mtu 9216 channel-group 10 mode active no shutdown NX9K2# show running-config <snip> feature vpc vpc domain 10 role priority 30 peer-keepalive destination 10.0.0.1 source 10.0.0.2 interface port-channel10 description vPC link - NX9K3 and NX9K4 switchport mode trunk mtu 9216 vpc 10 interface Ethernet1/3 description vPC link - NX9K3 switchport mode trunk mtu 9216 channel-group 10 mode active no shutdown interface Ethernet1/4 description vPC link - NX9K4 switchport mode trunk mtu 9216 channel-group 10 mode active no shutdown NX9K3# show running-config <snip> feature vpc vpc domain 20 role priority 20 peer-keepalive destination 10.0.1.2 source 10.0.1.1 interface port-channel20 description Link - Spines switchport mode trunk mtu 9216<