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How to create IPv6 subnet with prefix delegation

Tue Oct 12, 2021 2:28 pm

My ISP (Google Fiber) gives me an IPv6 prefix via delegation that then enables my Mikrotik router to distribute IPv6 addresses within that prefix to clients on my network. I now have 3 IPv4 subnets, each on their own VLAN, all connected to my Mikrotik router. IPv6 addresses are available only on my main subnet/VLAN. I'd like to have IPv6 on my other two subnets/VLANs, but I'm struggling to figure out how to do that on my Mikrotik router, given that the IPv6 prefix is dynamically assigned by my ISP. Is it possible, and if so can you point me in the right direction? Thanks!
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Re: How to create IPv6 subnet with prefix delegation

Tue Oct 12, 2021 7:24 pm

Generally you would start with your dhcp client to get the prefixes and add them to a pool:
/ipv6 dhcp-client
add add-default-route=yes interface=wan pool-name=comcast_ipv6 prefix-hint=::/60 request=address,prefix use-peer-dns=no
Then you just need to add an address to the the vlan interface that comes from the pool:
/ipv6 address
add from-pool=comcast_ipv6 interface=vlan10
add from-pool=comcast_ipv6 interface=vlan20
add from-pool=comcast_ipv6 interface=vlan30
You might need to modify the nd settings as well:
/ipv6 nd
set [ find default=yes ] advertise-dns=no disabled=yes
add interface=vlan10 other-configuration=yes ra-delay=5s ra-interval=5s-30s
add interface=vlan20 other-configuration=yes ra-delay=5s ra-interval=5s-30s
add interface=vlan30 other-configuration=yes ra-delay=5s ra-interval=5s-30s
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Re: How to create IPv6 subnet with prefix delegation

Wed Oct 13, 2021 6:59 pm

In addition to what @biomesh wrote ... there's a gotcha when dealing with IPv6 prefixes: many devices (Mikrotiks included) can only work with /64 prefixes on interfaces. If ISP gives out smaller prefixes (e.g. /60 or /56), then everything is fine and dandy. However, some ISPs only give out /64 prefixes and in this case it is not possible to create multiple IPv6 subnets. Even worse, some ISPs require that WAN interface of CPE uses address from given /64 prefix which makes whole prefix useless (it is not possible to use same prefix on two different routed interfaces).

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