It was a cold spring night and I was bored, so I decided to enter the future of the internet: IPv6.

How?

First, I setup IPv6 advertisements on my main interface (it was switch0):

set interfaces switch switch0 ipv6 dup-addr-detect-transmits 1
set interfaces switch switch0 ipv6 router-advert cur-hop-limit 64
set interfaces switch switch0 ipv6 router-advert managed-flag false
set interfaces switch switch0 ipv6 router-advert max-interval 30
set interfaces switch switch0 ipv6 router-advert other-config-flag false
set interfaces switch switch0 ipv6 router-advert prefix '::/64' autonomous-flag true
set interfaces switch switch0 ipv6 router-advert prefix '::/64' on-link-flag true
set interfaces switch switch0 ipv6 router-advert prefix '::/64' valid-lifetime 600
set interfaces switch switch0 ipv6 router-advert reachable-time 0
set interfaces switch switch0 ipv6 router-advert retrans-timer 0
set interfaces switch switch0 ipv6 router-advert send-advert true

This gave every client on my network it's own IPv6 address.

Next, I created the firewall rules to allow the tunnel to access my network:

set firewall name WAN_IN rule 100 source address 205.171.2.64
set firewall name WAN_IN rule 100 protocol 41
set firewall name WAN_IN rule 100 action accept

Since I had a dynamic IP address, I had to make a script to automatically update the IPv6 prefix for the tunnel.

I wanted it to run whenever the PPPoE IP changed, so I put it in the ip-up.d directory:

mkdir -p /config/scripts/ppp/ip-up.d
vi /config/scripts/ppp/ip-up.d/6rd-up

And the script:

#!/bin/bash

ipv4addr=$(curl -4 https://icanhazip.com)
ipv6addr="$(printf "2602:%02x:%02x%02x:%02x00::1\n" $(echo $ipv4addr | tr . ' '))"

echo "$ipv4addr -> $ipv6addr"

source /opt/vyatta/etc/functions/script-template

configure

delete interfaces switch switch0 address

# You'll want to change this to your IPv4 subnet

set interfaces switch switch0 address 10.0.0.1/24
set interfaces switch switch0 address ${ipv6addr}/64

delete interfaces tunnel tun0

set interfaces tunnel tun0 6rd-default-gw ::205.171.2.64
set interfaces tunnel tun0 6rd-prefix '2602::/24'
set interfaces tunnel tun0 address ${ipv6addr}/24
set interfaces tunnel tun0 description 'CenturyLink IPv6 6rd tunnel'
set interfaces tunnel tun0 encapsulation sit
set interfaces tunnel tun0 local-ip $ipv4addr
set interfaces tunnel tun0 mtu 1472
set interfaces tunnel tun0 multicast disable
set interfaces tunnel tun0 ttl 255

commit

# Firewall has to be set after tunnel is initialized

set interfaces tunnel tun0 firewall in ipv6-name WANv6_IN
set interfaces tunnel tun0 firewall local ipv6-name WANv6_LOCAL

commit
save
exit

At last, after a reboot, I finally had access to a whole new world: 2^128 of address space.

Performance

I was curious if the 6RD tunnel had any negative (or positive) performance impact so I ran some tests:

Latency

For the latency test, I simply ran ping -n 20 <ip> and took the average:

google.com (Seattle, WA, US)

First, I tested Google which is obviously going to have good results due to their proximity. This is mostly to check if the tunnel adds any inherent latency.

IPv4: min 5ms, avg 5ms, max 5ms
IPv6: min 5ms, avg 5ms, max 6ms

Not much to say here.

Scaleway VPS (Paris, FR)

Next, I tested a server in Paris (5,000+ miles away) to see if there was a bigger difference.

IPv4: min 150ms, avg 150ms, max 151ms
IPv6: min 145ms, avg 145ms, max 146ms

There's a reproducible 5ms decrease in latency.

Speed

For reference, I have a 1Gbps fiber connection and the following measurements are all megabits per second.

Fast.com/Netflix (Longview, WA, US)

I used fast.com—which is run by Netflix—for the first speed test.

IPv4: down 940mbps, up 910mbps
IPv6: down 770mbps, up 680mbps

Here we can see where the 6RD tunnel takes a real performance hit. 200-300mbps less.

ipv6-test.com (Paris, FR)

For the second speed test, I used ipv6-test.com which directly compares IPv4 vs IPv6 performance.

IPv4: down 50mbps
IPv6: down 454mbps

There is a ~400mbps improvement when compared to IPv4.

Let's try out the Quebec location as well:

IPv4: down 30mbps
IPv6: down 342mbps

Same thing here, a massive increase in throughput.

Conclusion

There doesn't seem to be a noticeable difference in daily browsing, but the Fast.com speed test is concerning, as I do a lot of egress/ingress over my connection and want to maximize throughput.

However the latency and throughput to distant locations seems is much better. I'd assume this is due to the tunnel having better peering to these locations. If you frequently download from servers in Europe, you may benefit from enabling the tunnel.

References

Thanks to the following resources from which some of this article was adapted:

If you followed this (tutorial?) and can't quite get it to work, feel free to comment below and I'll try my best to help.

Setting up CenturyLink 6RD on an EdgeRouter X