QoS for VxLAN Layer 3 Gateways

A VxLAN Layer 3 gateway allows inter-subnet communication through the VxLAN configuration. In the following figure, the leaf nodes act as the VxLAN Layer 3 gateway. Spine-1 and Spine-2 act as IP routing nodes that route the VxLAN packet out between Leaf-A and Leaf-B. Hosts on different subnets cannot learn MAC addresses of each other in a VxLAN network.

The leaf nodes resolve ARP for a tenant VM. The leaf nodes advertise the host routes to each other and tenant VMs with the next hop configured as VTEP. In the following figure, VM1 on a VxLAN network is sending a packet to VM3 on a VxLAN network.

VxLAN QoS DSCP:

At Ingress-VTEP, incoming packet‘s IP DSCP derives Traffic-Class (TC). Derived TC is then used to derive the outer DSCP value for VxLAN Encapsulated packet which is sent out via Tunnel Interface.

At the Egress-VTEP, incoming VxLAN encapsulated packet‘s outer DSCP value is used to derive Traffic-Class(TC). Post-Decapsulation, packet‘s VLAN PCP is derived from the TC derived above and, packet‘s DSCP value is derived based on “QoS-DSCP-mode” config.

For information on how to use the qos-dscp-mode command, refer the Extreme SLX-OS Command Reference for this release.

For VxLAN tunnel, the qos-dscp-mode configuration has no effect at ingress-VTEP.

The MCT ICL Tunnels are Internal VxLAN Tunnel. Behaviour explained about TC selection, DSCP and VLAN-PCP calculation for overlay-gateway is applicable to MCT Internal Tunnel as well. The MCT ICL Tunnel QoS model is “Pipe mode” always. As these are Internal VxLAN Tunnel, “Uniform Mode” is not applicable.

VxLAN QoS TTL:

VxLAN being virtualization Tunnel, VxLAN TTL model is “Pipe Mode” always. “Pipe mode” function is set both at Ingress-VTEP and Egress -VTEP.
AT Ingress-VTEP, VxLAN Header Outer TTL is a constant value (255). Inside the encapsulated packet, the incoming packet TTL (Payload TTL) is retained same.
Egress -VTEP validates VxLAN Header Outer TTL for non-Zero value, then discards it. Post Decapsulation, Payload TTL value is retained same.
The Payload TTL value gets decremented the number of times packet is routed. For example, symmetric routing will do one decrement at Ingress-VTEP and one decrement at the Egress-VTEP.
The MCT ICL Tunnels are Internal VxLAN Tunnel. VxLAN TTL behavior explained for Overlay-GW is applicable to MCT ICL internal Tunnel. The MCT ICL internal Tunnel TTL model is always in “Pipe mode”.

Configuration example

A prerequisite for configuring QoS is to configure the TCAM profile that supports Layer 3 gateway. For more information, see Configure the TCAM Profile for Layer 3 Gateway.

The qos-dscp-mode pipe command sets the QoS type mode to pipe, which is the default. The following example configures QoS-DSCP-mode support on a VxLAN gateway.

device(config)# overlay-gateway gateway_L3
device(config-overlay-gw-gateway_L3)# type layer2-extension
device(config-overlay-gw-gateway_L3)# ip interface loopback 1
device(config-overlay-gw-gateway_L3)# qos-dscp-mode pipe
device(config-overlay-gw-gateway_L3)# map vni auto 
device(config-overlay-gw-gateway_L3)# activate