Trying to get my head wrapped around a packet loss issue we're experiencing on a pair of Nexus Switches.
2x Nexus 3548's in VPC cluster
The Nexus switches are acting as the routing core for our network. The Nexus share OSPF routes to/from our firewall cluster on a stick for MPLS and internet.
We have a variety of edge switches + switch stacks connected to our Nexus core. Each switch has 2x 10GB fiber uplinks back to the nexus, split 50/50 between the two Nexus switches for redundancy. All uplinks are layer 2 LACP trunks.
Aside from this weird packet loss issue when routing between VLANs everything else seems to be working fine.
Packet loss issue is not reported when routing from internal VLANs outbound to the MPLS or internet. Issue only occurs between VLANs terminated to the Nexus.
Scenario: New server is connected directly to the Nexus switches, 1x 10gb cable to each switch in a VPC LACP etherchannel. Windows Server is set in LACP mode for load balancing. LACP comes online and traffic gets through. Uplink ports to the server are untagged on VLAN 40.
From a layer 2 perspective everything seems ok. The server can communicate with anything on the same VLAN without issue.
But when it tries to route to any of other other VLANs terminated on the Nexus we get about 50% packet loss. Instinct tells me that when packets are sent to Nexus A they get routed fine, but when the hit Nexus B the packets are being dropped or aren't getting routed.
Relevant config:
feature vrrp feature ospf feature interface-vlan feature hsrp feature lacp feature vpc feature lldp vrf context vpc_keepalive
vpc domain 5
peer-switch peer-keepalive destination 123.1.1.2 source 123.1.1.1 vrf vpc_keepalive peer-gateway auto-recovery spanning-tree vlan 1-3,10,40,50,80,101,200-205,2011,2020,2030 priority 0
interface Vlan10
no shutdown no ip redirects ip address 10.20.1.2/24 ip ospf passive-interface ip router ospf 100 area 0.0.0.0 hsrp 201 preempt delay minimum 300 priority 110 ip 10.20.1.1 interface Vlan40
no shutdown no ip redirects ip address 10.1.40.1/24 ip ospf passive-interface ip router ospf 100 area 0.0.0.0 hsrp 40 preempt delay minimum 300 priority 110 ip 10.1.40.5 interface Vlan101
no shutdown no ip redirects ip address 10.0.101.4/24 no ip ospf passive-interface ip router ospf 100 area 0.0.0.0 interface port-channel30
speed 10000 switchport switchport mode access switchport access vlan 40 vpc 30 interface Ethernet1/45
switchport switchport mode access switch access vlan 40 channel-group 30 mode active no shutdown 
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