Cisco Nexus 9000 Series Configuration Manual page 28

Guidelines and Limitations for VXLAN
• VPC peers must have identical configurations.
• For multicast, the VPC node that receives the (S, G) join from the RP (rendezvous point) becomes the
DF (designated forwarder). On the DF node, encap routes are installed for multicast.
Decap routes are installed based on the election of a decapper from between the VPC primary node and
the VPC secondary node. The winner of the decap election is the node with the least cost to the RP.
However, if the cost to the RP is the same for both nodes, the VPC primary node is elected.
The winner of the decap election has the decap mroute installed. The other node does not have a decap
route installed.
• On a VPC device, BUM traffic (broadcast, unknown-unicast, and multicast traffic) from hosts is replicated
on the peer-link. A copy is made of every native packet and each native packet is sent across the peer-link
to service orphan-ports connected to the peer VPC switch.
To prevent traffic loops in VXLAN networks, native packets ingressing the peer-link cannot be sent to
an uplink. However, if the peer switch is the encapper, the copied packet traverses the peer-link and is
sent to the uplink.
Note
• When peer-link is shut, the loopback interface used by NVE on the VPC secondary is brought down
and the status is Admin Shut. This is done so that the route to the loopback is withdrawn on the upstream
and that the upstream can divert all traffic to the VPC primary.
Note
• When peer-link is no-shut, the NVE loopback address is brought up again and the route is advertised
upstream, attracting traffic.
• For VPC, the loopback interface has 2 IP addresses: the primary IP address and the secondary IP address.
The primary IP address is unique and is used by Layer 3 protocols.
The secondary IP address on loopback is necessary because the interface NVE uses it for the VTEP IP
address. The secondary IP address must be same on both vPC peers.
• The VPC peer-gateway feature must be enabled on both peers.
As a best practice, use peer-switch, peer gateway, ip arp sync, ipv6 nd sync configurations for improved
convergence in VPC topologies.
Cisco Nexus 9000 Series NX-OS VXLAN Configuration Guide, Release 7.x
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◦ Consistent VLAN to VN-segment mapping.
◦ Consistent NVE1 binding to the same loopback interface
◦ Using the same secondary IP address.
◦ Using different primary IP addresses.
◦ Consistent VNI to group mapping.
Each copied packet is sent on a special internal VLAN (VLAN 4041).
Orphans connected to the VPC secondary will experience loss of traffic for the period
that the peer-link is shut. This is similar to Layer 2 orphans in a VPC secondary of a
traditional VPC setup.
Configuring VXLAN