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Q&A: Why Do I Need Redundant GRE Tunnels?

Question

  • Why Do I Need Redundant GRE Tunnels?
  • Why Do I Need 2 GRE Tunnels per router?

 

Environment

  • Silverline DDoS
    • Routed
    • GRE Tunnels

 

Answer

We require 2 GRE tunnels per router to ensure redundancy to each of our scrubbing centers. If we're connecting to one customer site, we'll build 2 tunnels from each of our scrubbing centers.

Note that despite the Portal naming convention of "IPv4 Tunnel Primary" and "IPv4 Tunnel Backup," this does not mean that the tunnels are active/passive.  If customer prefixes are advertised identically across two GRE tunnels, Equal Cost Multi Path (ECMP) routing will ensure load balancing between tunnels so as to not saturate one customer link.  For more information on load balancing, see: How do GRE Tunnel Load Balancing and Route Preferencing work?

A visual representation of the need for 4 tunnels:

 

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