1

I am testing a setup with 2 Nexus 3524 and a 2960X in a VPC Topology : enter image description here

For this test lab, I miss some SFP so there's only one physical link between each switch (and those link are copper using 1000BASE-T Copper SFP).

All 3 switches have VLAN 17 up and configured with an IP address:

Nexus 1 (left) : 192.168.17.254
Nexus 2 (right) : 192.168.17.252
2960X : 192.168.17.2

Both ports channel are trunk with VLAN 17 allowed.

When all links are up I can ping all addresses from any switch.

If I shutdown the link between 2960X and Nexus1 I got this:

  • 2960X can ping Nexus2
  • Nexus2 can ping Nexus1
  • 29060X cannot ping Nexus1

Note that the purpose is to use the Nexus as gateway for a bunch of VLAN with HSRP (also there will be 8 switches 2960X used as TOR, each with a VPC to the Nexus). HSRP is not configured yet as I want to have a working VPC configuration first.

Here are the configurations:
(all 3 switches are factory default settings apart from the configuration bellow, all interfaces not shown have no config at all)

Nexus 1

version 6.0(2)A1(1b)
hostname STA-TST-NEXUS1

no feature telnet
cfs eth distribute
feature interface-vlan
feature hsrp
feature lacp
feature vpc

control-plane
  service-policy input copp-system-policy

vrf context management
  ip route 0.0.0.0/0 10.22.110.254
vlan 1
vlan 17
  name test-17
vlan 18
  name test-18

vpc domain 100
  role priority 2000
  system-priority 4000
  peer-keepalive destination 10.22.110.12
  auto-recovery

interface Vlan1

interface Vlan17
  no shutdown
  ip address 192.168.17.254/24

interface Vlan18
  no shutdown
  ip address 192.168.18.254/24

interface port-channel10
  switchport mode trunk
  switchport trunk allowed vlan 17-18
  vpc 100

interface port-channel100
  switchport mode trunk
  spanning-tree port type network
  vpc peer-link

interface Ethernet1/1
  switchport mode trunk
  speed 1000
  channel-group 100


interface Ethernet1/23
  switchport mode trunk
  switchport trunk allowed vlan 17-18
  speed 1000
  channel-group 10 mode active


interface mgmt0
  no ip redirects
  ip address 10.22.110.11/24

Nexus 2

version 6.0(2)A1(1b)
hostname STA-TST-NEXUS2

no feature telnet
cfs eth distribute
feature interface-vlan
feature lacp
feature vpc

control-plane
  service-policy input copp-system-policy

vrf context management
  ip route 0.0.0.0/0 10.22.110.254

vlan 1

vlan 17
  name test-17

vlan 18
  name test-18

vpc domain 100
  role priority 3000
  system-priority 4000
  peer-keepalive destination 10.22.110.11
  auto-recovery

interface Vlan1

interface Vlan17
  no shutdown
  ip address 192.168.17.252/24

interface Vlan18
  no shutdown
  ip address 192.168.18.252/24

interface port-channel10
  switchport mode trunk
  switchport trunk allowed vlan 17-18
  vpc 100

interface port-channel100
  switchport mode trunk
  spanning-tree port type network
  vpc peer-link

interface Ethernet1/1
  switchport mode trunk
  speed 1000
  channel-group 100

interface Ethernet1/24
  switchport mode trunk
  switchport trunk allowed vlan 17-18
  speed 1000
  channel-group 10 mode active

interface mgmt0
  no ip redirects
  ip address 10.22.110.12/24

2960X

version 15.2
hostname STA-TSTSW1
!
switch 1 provision ws-c2960x-48td-l
!
spanning-tree mode pvst
spanning-tree extend system-id
!
vlan internal allocation policy ascending
!
lldp run
!
interface Port-channel1
 switchport mode trunk
!
interface FastEthernet0
 ip address 10.22.110.13 255.255.255.0
!
interface GigabitEthernet1/0/1
 switchport access vlan 17
 switchport mode access
!
interface GigabitEthernet1/0/2
 switchport access vlan 17
 switchport mode access
!
interface GigabitEthernet1/0/23
 switchport mode trunk
 shutdown
 channel-group 1 mode active
!
interface GigabitEthernet1/0/24
 switchport mode trunk
 channel-group 1 mode active
!
interface Vlan1
 no ip address
 shutdown
!
interface Vlan17
 ip address 192.168.17.2 255.255.255.0
!
ip default-gateway 10.22.110.254

So the question is: Why can't I ping between 2960X and Nexus1 when I cut a link?

Bonus: How to configure HSRP in this configuration?

5

For your first question, enable 'peer-gateway' under the VPC domain settings. This allows for directed ping forwarding over the VPC peer-link.

With core Nexus VPC peers, it is also recommended to set 'peer-switch' under the VPC domain settings and set their STP priorities for VPC vlans to the same values.

For your second question, HSRP is configured under the SVI on both N9k's:

N9k-1:

interface vlan 17
  no shutdown
  ip address 192.168.17.254/24
  hsrp version 2
  hsrp 17
    priority 110
    ip 192.168.17.1
    preempt

N9k-2

interface Vlan17
  no shutdown
  ip address 192.168.17.252/24
  hsrp version 2
  hsrp 17
    ip 192.168.17.1
    preempt

HSRP version 2 is not required here, default HSRP priority of 100. Verify HSRP is working between peers with 'show hsrp brief' and make sure you can ping all the various IP's.

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