vEdge Interface Queues – SD-WAN Design

By | 10/20/2021

Each vEdge interface has eight queues. Of these queues, queue 0 uses LLQ. By default, control and BFD traffic use queue 0. Control and BFD traffic is marked as DSCP 48 decimal. LLQ traffic is transmitted before packets in any of the other queues. The only congestion-avoidance algorithm used for this queue is tail drop, which treats all traffic equally and does not differentiate between classes of service. When the output queue 0 is full and tail drop is in effect, packets are dropped until the congestion is eliminated and the queue is no longer full.

Queues 1 through 7 use Weighted Round Robin (WRR) for scheduling. By default, user traffic uses queue 2.

When a packet passes from the service LAN to the transport, the following packet flow occurs on the vEdge router:

Local policy and configuration checks occur (including the policer, admission control, and classification marking).

Centralized application-aware routing policy is applied, with path selection based on the SLA.

Centralized data policy is enforced (including policer admission control, classification marking, and path selection).

Routing and forwarding occurs.

Packets are scheduled and queued (using LLQ, WRR, and RED).

Local policy shaping and ACLs are enforced (including shaping, a re-marking policer, and ACLs).

Multicast over SD-WAN

The Cisco SD-WAN solution supports PIM–Sparse Mode (PIM-SM) for multicast traffic over the overlay network. The Cisco SD-WAN solution optimizes multicast packet distribution by eliminating packet replication on the ingress router. The ingress router is the router that is connected to the multicast source. The ingress router forwards multicast streams to a vEdge router that is configured as a replicator.

As shown in Figure 11-15, the replicator vEdge forwards streams to multicast receivers. The PIM rendezvous point (RP) is not an SD-WAN device; vEdge routers do not support RP functionality. For distributing RP-to-group mapping information to local-site PIM routers, auto-RP is supported. vEdge routers support Internet Group Management Protocol (IGMP) version 2 to process a receiver membership report for hosts in a particular VPN to determine if traffic should be forwarded. PIM-SM, RP, and IGMPv2 are covered in Chapter 5, “IP Multicast and Network Management.”

Figure 11-15 Multicast Traffic Flow over SD-WAN

Cisco SD-WAN Cloud OnRamp

Cloud OnRamp provides connectivity between a customer’s on-premises infrastructure and a cloud service provider’s data center. This service is delivered through a virtual private connection, such as a VPN or a direct Internet connection. Cloud OnRamp provides improved application performance, optimized traffic routing, and reduced latency compared to public Internet connections.

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