Why BGP Load Balancing Is Not a Good Idea, Unless You Are AT&T

BGP load balancing is not the way to go for most of usEnterprises and mid-sized ISPs that have tried to implement BGP load balancing as a means to multi-home two or more gateways will immediately agree to the technical difficulties involved with setting up BGP. Configuring the optimal route announcements to other BGP peers to achieve a balanced traffic flow is difficult. Especially, load balancing inbound traffic to a multihomed network over several inbound paths is particularly challenging because of the limitations of the BGP route selection process.

Essentially, BGP load balancing requires the network administrator to divide a large IP address block into smaller blocks and tweak the route announcements to spread the blocks so that they look optimal on the different routes, as otherwise the external networks may all pick a specific route and create congestion on that one specific route.

As you probably have already guessed, BGP load balancing is not suited for your network unless you are a large telco with your own Autonomous Systems (AS) on the Internet. Aside from the difficulty of the BGP configuration and the difficulty in setting up the correct segmentation of network blocks, maintaining a correct balance on the traffic is difficult. Additionally, the granularity of the load balancing is very coarse.

So what is the best alternative if you’re a mid-sized ISP, or a mid-sized enterprise with several hundred branch locations, planning to implement load balancing? WAN Orchestrator devices, such as Broadband Bonding routers take a different approach to the multihoming of WAN connections. When the load balancing decisions are pushed to the higher OSI layers (higher than the IP layer), you no longer are confined with the restrictions and complications of IP routing and difficulties associated with route convergence. Granted, the higher layer approach still needs to comply with the IP routing standards, but that is achievable via overlay networks such as WAN Virtualization and Broadband Bonding. Similar to VPN overlays on IP networks, load balancing can be engineered to facilitate packet level routing decisions and therefore can achieve aggregation at a much finer granularity than flow tuples (source/destination IP, protocol, and port identifiers).

A Wan Orchestrator equipped with Broadband Bonding technology can practically create an overlay IP tunnel that can implement fine-tuned routing paths for packets, taking different paths, even within the same IP flow coming from the same flow tuples. Imagine VPN traffic from one branch office to a data center having its packets routed over multiple paths and therefore being dynamically optimized for certain parameters on the fly – this provides a much more adaptive multihoming than BGP can ever achieve.

If your organization is looking to implement multihoming to improve bandwidth capacity and/or reliability, an analysis weighing the pros and cons of  Broadband Bonding solutions compared to BGP load balancing would be very lopsided and heavily favor a WAN Orchestration solution.

Cahit Akin, CEO, Mushroom Networks, Inc.

Mushroom Networks is the provider of SD-WAN (Software Defined WAN) and NFV solutions capable of Broadband Bonding that enables self-healing WAN networks that route around network problems such as latency, jitter and packet loss.



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