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VeloCloud SD-WAN 7.0 - Administration Guide - Route Summarization Print

Route Summarization

Route Summarization or route aggregation provides a method to minimize the number of routes that a router advertises to its neighbor. It consolidates selected route prefixes into a single route advertisement. This differentiates it from regular routing, in which every unique route prefix in a route table is advertised to the neighbor.

Overview

Route Summarization or supernetting advertises a single route prefix instead of sending a bunch of contiguous route prefixes. However, with Route Summarization, there is a need to design the networks with summarization in mind,or there is a possibility for introducing suboptimal routing and forwarding traffic for unused networks. Similarly, the router drops the traffic if the routing table lacks a matching destination route prefix for the advertised summary prefix.

The Route Summarization feature requires a thorough network design analysis before specifying the summarized prefix for advertisement to neighbors.

Route Summarization Use Case

In the example topology, a router learns route prefixes from multiple sources. When the router advertises route prefixes to its neighbor via BGP, it advertises the unique route prefixes.The router advertises eight unique route prefixes. Instead, with Route Summarization, the router can advertise a single summary prefix to the neighbor through BGP.

Figure 1. Example Topology for Route Summarization
VeloCloud SD-WAN Edges and Gateways now feature Route Summarization functionality.
  • In the case of the VeloCloud SD-WAN Edge:
    • Summary prefix via BGP to a neighbor set up over a Routed (LAN) interface
    • Summary prefix via Border Gateway Protocol to a neighbor set up over an NSD (IPsec/BGP) tunnel
    • Summary prefix via OSPF to a neighbor set up over a Routed (LAN) interface
  • In the case of the VeloCloud SD-WAN Gateway:
    • Summary prefix via BGP to a neighbor set up over NSD (IPsec/BGP) tunnel
    • Summary prefix via BGP to a Partner Hand off router over the Partner Hand off Interface

Black Hole Routing

A black hole route, or a null route, is a network route that discards incoming traffic. In Route Summarization, the system utilizes black hole routing to drop traffic for destinations that belong to a summary route but lack a locally learned prefix. Starting with release 5.2, the system requires this process because advertising a summary route directs all traffic for that supernet to the Edge or Gateway—including traffic for non-existent destination prefixes. Configuring a summary route automatically installs a black hole route for that prefix in the routing table until the system removes the configuration.

Configure Route Summarization

Starting with the 5.2.0 release, users can configure the Route Summarization feature in the Orchestrator UI for the following topics.

Route Summarization Configuration
Note: For an overview, use case, and information about black hole routing for Route Summarization, refer to Route Summarization.
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