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Posts: 33
Registered: ‎10-21-2015

LRT224 WAN Failover IPv6

I have the LRT224 setup in dual WAN mode with Charter Spectrum on WAN1 and ATT Uverse on WAN2.

 

WAN1 IPv6 block: 2600:C640:xxxx:xxxx

WAN2 IPv6 block: 2602:0304:xxxx:xxxx

 

I normally have WAN1 configured as primary using Link Failover only. But, tonight I encountered a connectivity issue that I thought might be IPv6 related. I switched to WAN2 as the primary. This moved all of my IPv4 traffic over to WAN2 (ATT). However, my IPv6 traffic is still going down WAN1 (Charter). This is easily verified by going to ipv6-test.com (or any other IP discovery site). Sure enough, endpoints see my IPv4 address as ATT and my IPv6 as Charter. Note, I am NOT using Load Balance or Sticky Balance. It is definitely set to Link Failover only.

 

Has anyone else encountered this issue?

How do I make IPv6 move to the other WAN when a link failover occurs?

Is this a bug?

 

I can reproduce this like clockwork everytime. Rebooting the router doesn't fix it.

Expert
Posts: 13,604
Registered: ‎01-18-2013

Re: LRT224 WAN Failover IPv6

Did you try shutting down or completely disconnecting WAN1 since it's actually not down?


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Linksys
Communities Technical Support
Expert
Posts: 13,604
Registered: ‎01-18-2013

Re: LRT224 WAN Failover IPv6

Interesting problem Smiley Happy


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Linksys
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Posts: 33
Registered: ‎10-21-2015

Re: LRT224 WAN Failover IPv6

I'll do some more testing and see what actions cause what behaviors.

 

One thing I've always found interesing is that on the router status page under the WAN section I will see the IP addresses and whatnot filled in for WAN1 but blanked out for WAN2 on the IPv4 tab when WAN1 is active. Once WAN2 becomes active WAN1 addresses are blanked out and WAN2 is filled in. However, on the IPv6 tab the addresses for both WAN1 and WAN2 are always shown regardless of which WAN connection is active.

 

This leads me to believe that WAN failover for IPv6 is handled separately from IPv4. The question is whether it is by design or a bug.Ya know...IPv6 isn't NAT'd so I'm wondering if that somehow plays a role. I can't imagine any way that this isn't a bug though  I mean, if I intentionally make WAN2 the primary I expect all traffic (IPv4 and IPv6) to use WAN2. In fact, my clients shouldn't even be getting an IPv6 address from WAN2...or should they? 

 

Anyway, I'm going to play around with this and update the thread as I get time.

Expert
Posts: 13,604
Registered: ‎01-18-2013

Re: LRT224 WAN Failover IPv6


bdginmo wrote:

I'll do some more testing and see what actions cause what behaviors.

 

One thing I've always found interesing is that on the router status page under the WAN section I will see the IP addresses and whatnot filled in for WAN1 but blanked out for WAN2 on the IPv4 tab when WAN1 is active. Once WAN2 becomes active WAN1 addresses are blanked out and WAN2 is filled in. However, on the IPv6 tab the addresses for both WAN1 and WAN2 are always shown regardless of which WAN connection is active.

 

This leads me to believe that WAN failover for IPv6 is handled separately from IPv4. The question is whether it is by design or a bug.Ya know...IPv6 isn't NAT'd so I'm wondering if that somehow plays a role. I can't imagine any way that this isn't a bug though  I mean, if I intentionally make WAN2 the primary I expect all traffic (IPv4 and IPv6) to use WAN2. In fact, my clients shouldn't even be getting an IPv6 address from WAN2...or should they? 

 

Anyway, I'm going to play around with this and update the thread as I get time.


Typically a WAN configuration change of this sort may require a reboot.


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Linksys
Communities Technical Support
Posts: 33
Registered: ‎10-21-2015

Re: LRT224 WAN Failover IPv6

Rebooting doesn't seem to have an effect on whether it picks the primary WAN connection for IPv6 traffic. It always picks WAN1 even if WAN2 is primary. 

 

I'll simulate some actual link failures by pulling the ethernet cables out of the WAN ports later. My router is downstairs and I'm too lazy to fiddle with it tonight.

Posts: 12
Registered: ‎01-21-2015

Re: LRT224 WAN Failover IPv6

Hi, bdginmo,
When you switched to WAN2 as the primary, you will see your PC (MS Windows) obtains a new IPv6 address of WAN2 prefix, but also keeps the original IPv6 address of WAN1 prefix.
Your PC will choose original IPv6 address (for WAN1) as source address when you access internet. That causes IPv6 traffic go through WAN1.
To resolve this issue, you can open [Control Panel > Network and Internet > Network Connections] page on your PC (MS Windows).
To "Disable" and then "Enable" Ethernet, IPv6 address for WAN1 will be released in your PC. Then IPv6 traffic goes through WAN2.

Posts: 33
Registered: ‎10-21-2015

Re: LRT224 WAN Failover IPv6

I'm pretty sure all of my devices get both the WAN1 and WAN2 IPv6 prefix all of the time and regardless of which WAN is primary. Since I have 2 addresses I'm guessing the OS's prefix policy is somehow choosing the WAN1 IP not because WAN1 is primary on the router but maybe because of some obscure heuristics in Windows. Since outgoing packets are tagged with the WAN1 IP the router naturally sends it out WAN1.

 

Let me play around with what you suggest tonight and I'll see what happens, but I'm pretty sure I'll still get both IPv6 prefixes.

Posts: 33
Registered: ‎10-21-2015

Re: LRT224 WAN Failover IPv6

So after playing around with this I've concluded that the LRT224 will advertise the IPv6 prefixes of both WAN interfaces regardless of which one is the primary. That means my clients will get both IPv6 address prefixes. I highly suspect Windows is preferring the WAN1 address due to either the prefix policies or possibly because of some other heuristic.

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Posts: 33
Registered: ‎10-21-2015

Re: LRT224 WAN Failover IPv6

Here are the results of more tests.

 

When I pull the cable out of a WAN port:

 

The IPv4 side failsover nicely. And since clients are NAT'd they don't even really know what happened.

 

The IPv6 prefix from that WAN interface is no longer advertised by the router. That's expected. The problem is that clients (or at least my Windows PC) retains the IPv6 address in that block and is not smart enough to use it's other IPv6 address from the other WAN interface prefix. You have to disconnect/reconnect your network interface on the client to move the IPv6 traffic. At least from the router's persepctive I think this is expected behavior because IPv6 isn't NAT'd. Windows could use some work on how it handles multiple IPv6 address assignments.

 

When I sabotage the WAN interface gateway device (cable modem):

 

Same as above, but it takes a little longer for the failover to happen. Overall, not bad though.

 

When I switch the primary WAN interface in the LRT224 configuration:

 

IPv4 traffic moves over to the other WAN. The router continues to advertise both WAN interface IPv6 prefixes because both WANs are active. The client is deciding which IP address to use and thus which WAN interface it's IPv6 traffic is routed though.