NMC DOiT Vol.2 Scenario 7 Day 4-4 – RIPng Unequal-Cost Load-Balancing


I wasn’t going to blog about this scenario anymore, but this one issue is so freaky, I just have to. The scenario asked for RIPng to load-balance IPv6 traffic over the ethernet and serial links in a 2:1 ratio. So, for every packet routed over the serial, 2 would go over the ethernet link. My brain pondered this, and after maybe 3 seconds of contemplation, I didn’t even try to figure it out. I didn’t know of any feature that would allow me to do anything other than equal-cost load-balancing, so I skipped right to the answer key. And, in truth, there is no such thing other than equal-cost load-balancing. This is one of those “think outside the box” solutions.

The answer is to create a tunnel that goes over the ethernet link, run RIPng over it, and tweak the metric with “metric-offset” so that the tunnel comes up as an equal-cost path along with the ethernet and serial. So, RIP will think it has 3 paths – the tunnel, the ethernet, and the serial. 1 packet will go over the ethernet encapsulated as a tunnel packet. 1 will go over ethernet natively. 1 will go over serial. Thus, a 2:1 ratio in favor of the ethernet.

If I ever saw someone trying to put this into production on my network at work, I’d kill them outright, and wouldn’t feel bad about having done so.

By Ethan Banks

Ethan Banks is a podcaster and writer with a BSCS and 20+ years in enterprise IT. He's operated data centers with a special focus on infrastructure — especially networking. He's been a CNE, MCSE, CEH, CCNA, CCNP, CCSP, and CCIE R&S #20655. He's the co-founder of Packet Pushers Interactive, LLC where he creates content for humans in the hot aisle.