Pass ipv6 prefix to downstream router

[liug]

Does Asus/Merlin support passing ipv6 prefix to downstream router?

Current setup:
ISP -> Asus/Merlin router 1 -> LAN1

Router 1 is configured Native IPv6 with PD. Prefix size 64 and it is used on LAN 1 with Stateless. Everything works.

The plan is to add a downstream router:
ISP -> Asus/Merlin router 1 > LAN1 -> Asus/Merlin router 2 -> LAN 2

Since ISP supports PD prefix /60, can router 1 use prefix size 60 and pass one /64 to router 2 to be used for LAN 2?

 

[dave14305]

Only dnsmasq exists on the router to do DHCPv6 downstream and I don’t see that it supports downstream prefix delegation.

 

[RMerlin]

You have to do it manually. I do it here so I can have a /64 taken out of my delegated /56, assigned to a development router.

On the main router: on start, you need to configure a route. In my case, for example:

ip -6 route add 2600:1000:1000:1001::/64 via fe80::1111:1111:1111:1111 dev br0

Configure the appropriate prefix. The via will be the link-layer IPv6 of the downstream router's WAN interface (typically eth0)

On the downstream router: set IPv6 to Native, disable PD, and configure the LAN to your assigned /64.

Clients connected to LAN2 will get an IP from that subnet.

 

[liug]

Will it work if I configure the second router using IPv6 Passthrough, instead of Native? Will that make LAN2 clients get IPs from LAN1?

 

[liug]

You have to do it manually. I do it here so I can have a /64 taken out of my delegated /56, assigned to a development router.

On the main router: on start, you need to configure a route. In my case, for example:

ip -6 route add 2600:1000:1000:1001::/64 via fe80::1111:1111:1111:1111 dev br0

Configure the appropriate prefix. The via will be the link-layer IPv6 of the downstream router's WAN interface (typically eth0)

On the downstream router: set IPv6 to Native, disable PD, and configure the LAN to your assigned /64.

Clients connected to LAN2 will get an IP from that subnet.

Since I don’t have static IPv6, does that mean each time router 1 is rebooted, it will get a different PD? So we have to manually update router 2 for LAN 2 to use the new prefix .

 

[RMerlin]

Will it work if I configure the second router using IPv6 Passthrough, instead of Native? Will that make LAN2 clients get IPs from LAN1?

No idea what Passthrough mode does exactly.

Since I don’t have static IPv6, does that mean each time router 1 is rebooted, it will get a different PD? So we have to manually update router 2 for LAN 2 to use the new prefix .

If the delegated prefix is dynamic then yes, you would need to adjust that route every time, as well as the LAN prefix on the second router.

Any ISP that offers to delegate a whole /60 or /56 should have the common sense to make it static - anyone who needs something larger than a /64 will most definitely need that to be static, otherwise how else are they expected to subnet that. Sadly, a lot of ISPs are managed by idiots... Thankfully mine isn't. They offer a dynamic /64, and on request they will assign you a static /56.

Might be worth asking them about making that /60 static. Maybe if enough people ask for it, they might adjust.

 

[liug]

I did more searching in this forum and found this old post which indicates using IPv6 passthrough mode on router 2 will work. I assume in this setup, the LAN 2 will use the same /64 from LAN 1 subnet.