Multi-WAN setups with retail ISPs (Part 1 – Theory)

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This will be a series containing multiple parts (which I may add in the future):
Part Two

In part one, I would like to talk about a particular networking environment where a site (home, office etc) has more than one uplink either to the same or a different ISP, where the ISP(s) are retail meaning “home grade” ISPs or “consumer” ISPs instead of dedicated leased circuits/business-grade ISPs.

Definition

I could not find a textbook definition for Multi-WAN as it is an umbrella term for many things such as Multi-WAN based load balancing, Multi-WAN based failover etc.

My definition of Multi-WAN is fairly straightforward i.e. A router/network/site that has more than one uplink to an ISP or a different ISP is a Multi-WAN setup.

Pros

• Significantly cheaper than dedicated leased circuits
  • Can be deployed for SOHO, Small Businesses and perhaps even enterprise (private firms that do not require their own ASN)
• Redundancy/Failover/High Reliability
  • If one uplink goes down, traffic is routed over the next available uplink
• Load Balancing
  • Where traffic is split/balanced between the available uplinks
  • Bandwidth aggregation is also possible without any bonding or routing protocols like ECMP i.e. in other words, you can achieve increased bandwidth throughput in downloads/uploads by using the available bandwidth from the uplinks simultaneously
• You can route specific destination IPv4/IPv6 addresses/prefixes via a specific WAN interface that happens to have better routing to the said subnets (example: ISP2 has lower latency to Cloudflare’s DNS resolvers when compared to ISP1)
  • I have done exactly just this here

Cons

• Total cost may be higher for the initial installation of CPE/ONT/Router/Switches etc but this is usually negligible
• You will not have SLAs like dedicated lines but this is somewhat mitigated by having multiple uplinks
• If a proper configuration is not done, HTTPS traffic will break (for example banking sites) since the source IPs would change frequently
• The monthly cost of the ISPs combined may or may not be higher depending on the available tariffs in that particular area
  • For example, if ISP1 had a ₹500 tariff and the other had ₹300, then the total monthly cost is pretty cheap in my opinion
• Likely behind an ugly CGNAT deployment
  • And likely that they will not provide a public IP as their IPv4 pools are again likely to be exhausted
  • Also likely that they will only give a single /64 IPv6 prefix which makes subnetting impossible without breaking SLAAC (Read Android)

Real-Life Example

I have deployed a Multi-WAN environment in my own home using RB450Gx4 as the router where

• ISP1 (AS9829) has a 200Mbps symmetrical bandwidth (at the time of deployment/testing)
• ISP2 (AS135756) has a 100Mbps symmetrical bandwidth (at the time of deployment/testing)
• Monthly Tariffs (at the time of deployment/testing)
  • ISP1 – ₹1277
  • ISP2 – ₹1375

The end result of my setup is demonstrated below