[SASAG] Comcast & IPV6 + Dlink router

Kurt Buff kurt.buff at gmail.com
Mon Nov 9 19:56:50 PST 2015

fe80 addresses are generated independently by each host, not handed
out by your ISP - they are *only* used within a subnet, and never (I'm
99+% sure) across a layer3 boundary, and therefore don't need central
administration. If you were to hook two machines together that have
IPv6 stacks with a dumb switch, and having no other connectivity, they
would each generate their own fe80 addresses and be able to talk with
each other over IPv6. This is distinct from other classes of IPv6
addresses, such as locally unique addresses (LUAs, a rough analog of
rfc1918 addresses, which can be assigned via DHCP) and probably a
couple of other special sets of addresses that I'm not remembering, at
least one of which has been deprecated.

Now, this doesn't mean that the problem isn't with Comcast - it quite
possibly is, but it's also possible that your equipment, while not
defective in any way, either isn't getting an address from Comcast, or
doesn't understand the way that they are handing out addresses.

For diagnosing that, you'll need to find someone clueful at Comcast.


On Mon, Nov 9, 2015 at 7:31 PM, Bill Levering <idbill at planx.com> wrote:
> Hmm… seems like maybe it’s a Comcast issue.
> The comcast6.net website hasn’t been updated in over a year, and the deployment FAQ is from 2012.
> This is listed as my gateways on the router:
> Gateway, fe80::223:ebff:fe77:92e2
> and this shows up in the ipv6 routing table on the router:
> ::/0                                        fe80::223:ebff:fe77:92e2                UGDA  1024   27       0 eth1
> ::/0                                        fe80::c612:f5ff:feed:d932               UGDA  1024   661       0 bdg1
> So, my guess, is the fe80 address is coming from comcast.
> Bill
>> On Nov 9, 2015, at 5:24 PM, Benjamin Cline <brc at peppermint.org> wrote:
>> That fe80::/64 address you're seeing is an IPv6 link-local address, it sounds like you're not getting a valid routable IPv6 subnet assigned to the LAN side.
>> I have a similar setup and at one point I was able to get Comcast to assign a routable /64 to my lan via DHCP-PD[1], but that stopped working after about a month and I wasn't able to get it fixed. I considered it unlikely I'd be able to get through to someone who actually understood my problem and could fix it, so I didn't bother calling support.
>> [1] https://en.wikipedia.org/wiki/Prefix_delegation
>> On Mon, 9 Nov 2015, Bill Levering wrote:
>>> So… I upgraded to a D-Link DSR-250 router and was hoping to get IPV6 working.
>>> It appears that the router is getting an IPV6 address, and I can ping IPV6 addresses from it, but I can’t reach anything from my Mac.
>>> Comcast support tells me that they don’t support IPV6!
>>> All the D-Link pages I’ve found don’t show 1/4 of the options I have available to me.
>>> Such as:
>>> - IPV6 WAN settings
>>> - IPV6 LAN settings
>>> - Router Advertisement
>>> - Advertisement Prefixes
>>> - Prefixes for Prefix Delegation
>>> My gateway appears to be: fe80::c612:f5ff:feed:d932%en0
>>> which makes me think it is hitting localhost on the router.
>>> I think it is probably something in my config, but I don’t know where to start.
>>> Any ideas?
>>> Bill
>>> _______________________________________________
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>> --
>> Benjamin R. Cline
>> brc at peppermint dot org
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