Nexus 5000 + HSRP + VPC

[Ferenc Kuris]

Hello,

I have noticed an interesting output on our N5Ks. Topology

N5K-1 -------- N5K-2

    |                  |

    |                  |

          VPC

    |                 |

       C3750X

N5K-1 is our primary HSRP node, the other N5K is the secondary. I have configured Port-Channel on the 3750X towards the N5Ks and VPC on the N5Ks toward the 3750X. simple topology.

When I do a traceroute, based on SRC-DST IP (even or odd destination), active and standby nodes answers the UDP requests. On N7Ks and other Cisco devices, only the primary node answers the request - this should be the normal behavior.

On the 3750X, I see only the VIP address in the ARP table.

Internet  192.168.237.33          35   0000.0c9f.f001

Tracing the route to 1.1.1.5
VRF info: (vrf in name/id, vrf out name/id)
  1 192.168.237.34 0 msec 0 msec 0 msec

Tracing the route to 1.1.1.2
VRF info: (vrf in name/id, vrf out name/id)
  1 192.168.237.35 0 msec 0 msec 0 msec

Why is the packet answered by the secondary node? Any ideas?

NX-OS version  5.2(1)N1(1)

[Manoj Papisetty · Accepted solution]

On the Nexus platform, peers configured with HSRP with vPC work in "Active-Active" mode rather than "Active-Standby". Both the Nexus devices will respond to the VIP and this is what you are seeing in your setup too. This is an expected behaviour. 

You can look into the vPC and HSRP section (Page 79) in this guide here - http://www.cisco.com/c/dam/en/us/td/docs/switches/datacenter/sw/design/vpc_design/vpc_best_practices_design_guide.pdf