IPV6
Internet Protocol Version 6
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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
      }
      prefix-only
      rapid-commit disable

    }

  }

}

 

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

6 REPLIES 6
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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.

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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

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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.

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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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Re: Got IPv6 Working on Cisco DPC3941B

I encountered the same difficulty as this other customer:

 

https://forums.businesshelp.comcast.com/t5/IPV6/IPv6-routing-on-DPC3941B-in-pass-through-mode/td-p/3... 

 

Basically, I get assigned a /59, just like you.  (And confirm I also can't get larger than a /59 either.)

 

But it appears that it does not actually create a route on the DPC3941B cablemodem: trying to ping any of the hosts results in IPv6 ND "neighbor discovery" requests being sent, which clearly indicates a route is missing.  So I can ping my router from the outside (and inside as well), but I can't ping a host on one of the subnets.

 

In general, I'd expect the DPC3941B cablemodem to create the route when it gives out the delegation.  But it isn't doing that.  A backup would be to create a static route, but while there's options on the cablemodem portal to create IPv4 static routes, there's no obvious way to create IPv6 static routes.

 

Can anyone confirm they actually got it to route through their gateway, as opposed to just delivering to devices directly connected on the WAN ethernet segment?

 

I wonder if it's possible that some minor DHCP configuration change might make it not automatically create the route.  I am using pfSense like Veddy254 so that gives me some confidence that this should work.

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Re: Got IPv6 Working on Cisco DPC3941B

Sadly, I've since dropped the Static IPs add-on from my business account and I don't remember all that I went through to get it working as best as possible given the issues with IPv6 and this particular gateway. But I do know what I have checked in my WAN interface under DHCP6 Client Configuration (ignore the /56 in the following screen snippet)chrome_0016.png

 

Debug probably isn't required but I had it set so I could get more verbosity out of PfSense.

 

Hope this helps,

Veddy

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