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Got IPv6 Working on Cisco DPC3941B

Occasional Visitor

Got IPv6 Working on Cisco DPC3941B

I decided to come back to this after some time and got it all working. I hope this helps folks.


I have a Cisco DPC3941B and a Ubiquiti EdgeRouter Lite

I have a static IPv4 block (/29) and a static IPv6 block (/56)

My delegated prefix is 2603:xxxx:xxxx:d000::/56

My gateway is using 2603:xxxx:xxxx:d000::/64

I am able to perform prefix delegation for 2603:xxxx:xxxx:d0e0::/59

Attempts to use larger prefixes fail

That still gives me 32 /64 subnets (2603:xxxx:xxxx:d0e0::/64 - 2603:xxxx:xxxx:d0ff::/64)

eth0 = WAN

eth1 = LAN

eth2 = WLAN


Here is the basic config that worked for me.



interfaces {
  ethernet eth0 {
    address 75.xxx.xxx.129/29
    dhcpv6-pd {
      pd 0 {
        interface eth1 {
          host-address ::1
          service slaac
        interface eth2 {
          host-address ::1
          service slaac
        prefix-length 59
      rapid-commit disable





You could keep going and configure specific PD options, stateless DHCPv6, IPv6 firewall rules, etc. Hopefully this will get you started.

New Member

Re: Got IPv6 Working on Cisco DPC3941B

PfSense has it a bit different in that the LAN has to be statically set, but I too get the /59.


EDIT: Also, I'm able to do stateful DHCPv6 through that method as well. If there are people who would like the steps I used to do that, I can post them. I haven't done any prefix delegation though and I suspect that I'd have to have another PFsense box in order to do that reliably, but I could be wrong.

Occasional Visitor

Re: Got IPv6 Working on Cisco DPC3941B

Hi Veddy254,


I have been trying to get IPv6 working on my IPsense enviroment, If you could post your steps I would appreciate it.


Thank you

New Member

Re: Got IPv6 Working on Cisco DPC3941B

Sadly, it seems to have quit and I'm not sure why. I will parse through my logs here and try to figure out why it crapped out.


EDIT: So it seems to break after a week and I think I finally figured out why. My way seems to have involved temporarily doing a LAN - Track Interface -> WAN with PD-ID 0 and then swapping over to static which works... until the DHCP lease runs out on the DPC3941B for the original prefix request via Track Interface.


EDIT #2: BREAKTHROUGH! Logged into the gateway device and set the DHCP lease time to Forever (DISCLAIMER: now if the modem reboots, this likely will crap out but at least it's an easy albeit bothersome fix.) Had the LAN interface pick up Prefix ID 0 via Track Interface -> WAN. Let the LAN side get an IP then swapped it over to a static /59 with the Prefix ID 0 being the parent (2603:xxxx:yyy:e0:: is how my /59 looks with the Prefix ID as 0). I then defined my prefix delegation as e1 through ff (2603:xxxx:yyy:e1:: in the from field, 2603::xxxx:yyy:ff:: in the to field) as my prefix delegation range which means that anything other that e0 is an IPv6 prefix that I can delegate out as a separate /64. Confirmed IPv6 connectivity on my desktop.


Re: Got IPv6 Working on Cisco DPC3941B

Is this still working for you? Is there any way I could please see your settings? I'm stumped over here.

I have a static /30 for IPv4 and a /566 for IPv6. Cannot get my WAN NIC to get an address for the life of me. 

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