IPv6 Setup with Comcast/Xfinity

JohnD5000

Regular Contributor
Any info on how to setup IPv6 with comcast/xfinity? Connection type ative, passthrough, etc? What about settings for DNS?

Thanks
 

Kingp1n

Very Senior Member
Any info on how to setup IPv6 with comcast/xfinity? Connection type ative, passthrough, etc? What about settings for DNS?

Thanks
Passthrough doesn't work for me...only native.
 

Mutzli

Very Senior Member
Passthrough doesn't work for me...only native.
Same here, It should be set to native. Passthrough is a bridging mode to connect devices to IPv6. It comes with lots of disadvantages over a full native IPv6 implementation.
 

5stringdeath

Regular Contributor
Same here, It should be set to native. Passthrough is a bridging mode to connect devices to IPv6. It comes with lots of disadvantages over a full native IPv6 implementation.
Same is true for me, although I use FiOS in an area that actually has IPv6 working. Is Comcast fully implemented everywhere?

If you're intersted in how limited the FiOS rollout is there is a long thread here.

Native = 10/10 score
Passthrough = 0/10 score

I did manually enter Cloudflares IPv6 DNS settings, but I'm not sure if I needed too. Does it respect the IPv4 settings, or would it automatically use Verizon's if I left it set to "Enable"?
 

Netbill

New Around Here
Any info on how to setup IPv6 with comcast/xfinity? Connection type ative, passthrough, etc? What about settings for DNS?
JohnD5000: Here is my setup with Comcast (I have my own SB6141 modem) I just set drop down to "native" (also ensure the firewall is tuned on under "Firewall") and IPv6 test fine with reliable connection.
upload_2020-2-22_9-57-12.png


hope this helps -- Added: I use the Merlin default DNS in my setup, only adjustment there is I turn off UPnP
 
Last edited:

EmeraldDeer

Very Senior Member
IPv6.png
 

EmeraldDeer

Very Senior Member
Cloudflare_DNS_TLS.png
 

Mutzli

Very Senior Member

EmeraldDeer

Very Senior Member
IPv6 DNS Setting can be set to Disable if you want to specify another DNS resolver than your ISP's. Mine points to Cloudflare:
View attachment 21546
That's right.

My take on this is:
  • I am looking for the most trouble free router boot process
  • I am not concerned if lookups are going Comcast as the router boots before DNS over TLS startup has completed
  • Accordingly, I just take the IPv4 and IPv6 DNS servers which the Comcast DHCP server hands out (or however IPv6 does this)
  • After DNS over TLS starts, I am using Cloudflare for IPv4 and IPv6 DNS
  • I am in a suburb of a city which has a Cloudflare data center. It is about 6 hops and 10 msec away. I am not paying a performance penalty outside of what is inherent to DNS over TLS, although more knowledgeable folks have stated that DNS performance would need to be very bad for you to notice.
 
Last edited:

anonimo

New Around Here
Any info on how to setup IPv6 with comcast/xfinity? Connection type ative, passthrough, etc? What about settings for DNS?

Thanks
"NATIVE" along with all other default settings will permit you to setup/test IPv6 on comcast/xfinity. The additional recommendations above may come in handy, depending upon your needs. I don't recall needing to reboot, but you may need to afterwards to show your IPv6 address on the firmware page.

VPN software may disable IPv6 in the adaptor settings (mine did at install and during software upgrades), because IPv6 is not routed through their VPN tunnel and leak your location.
 
Last edited:

Keenan

Senior Member
Passthrough doesn't work for me...only native.
I was set to Native but upon testing to respond to this thread it said no connectivity. I recently switched modems from a Motorola 8600 to Comcast's Technicolor CGM4140COM and now I'm wondering if that's the reason why. It's a gateway device but it is currently set in bridge mode and is connected to my RT-AC86U. The passthrough setting does give connectivity but I see from other posts here that that is not a desirable solution.
 

JohnD5000

Regular Contributor
That's right.

  • I am in a suburb of a city which has a Cloudflare data center. It is about 6 hops and 10 msec away. I am not paying a performance penalty outside of what is inherent to DNS over TLS, although more knowledgeable folks have stated that DNS performance would need to be very bad for you to notice.
I noticed your from Mass. Where is Cloudfare data center? I'm also from Mass and currently using Quad9. Wondering if should switch to CF? Thanks
 

JohnD5000

Regular Contributor
Thanks for all the answers. 1 question:

What does "Enable Router Advertisement" do. Why set to Enable or disable?
 

appleseed

Regular Contributor
It will push your router's IP in addition to user-specified DNS to all your devices. If you enable, it will use the routers own cache + user-specified DNS, or disable, and it will bypass the local cache and always go to the user-specified DNS. I always use yes, because I have a simple home network. Others use no because they are running specialized programs/scripts.
 

JohnD5000

Regular Contributor
It will push your router's IP in addition to user-specified DNS to all your devices. If you enable, it will use the routers own cache + user-specified DNS, or disable, and it will bypass the local cache and always go to the user-specified DNS. I always use yes, because I have a simple home network. Others use no because they are running specialized programs/scripts.
Thanks, I'm still a little fuzzy on it. I've set "Connect to DNS server automatically" to disable and set up Quad9. Will the "Enable Router Advertisement" set to enable push the Comcast DNS or the Quad9 DNS? Or should I set it to disable to always use Quad9?
 

appleseed

Regular Contributor
Connect to DNS server automatically: disable (here you are saying you do not want the ISP DNS)
DNS Server 1: (fill in, here you are saying you want your own DNS and do not want the ISP DNS)
DNS Server 2: (fill in, here you are saying you want your own DNS and do not want the ISP DNS)
Advertise router's IP in addition to user-specified DNS: yes*

*Or no, depending on your needs. I think the cache latency can be just as fast/faster under certain circumstances. HOWEVER, set this to no if you venture into scripting and other programs, or set it to no for any reason you like and compare it with yes. When set to no, all devices will bypass any local cache and instead use the user-specified DNS**.

**some devices come with their own hard-coded DNS
 

JohnD5000

Regular Contributor
So Enable Router Advertisement advertises routers IP & DNS to my network, not outside network? If I have "Connect to DNS server automatically" to disable and set up Quad9, wouldn't Quad9 be set to locale cache anyhow? So, setting Router Advertisement to enable or disable would be the same thing? Or am I just really not getting what this setting does?
 

appleseed

Regular Contributor
It will make more sense when you look at each device individually, by going to each devices' Internet/DHCP settings, and see how they change depending on router settings above.
 

Kal-EL

Very Senior Member
I have my RT-AC86U set to "Passthrough" and it passes the IPv6 test at the below link.

https://test-ipv6.com/
Be advised using IPv6 in passthrough is a bad idea. Passthrough does just that it passes right through with no active firewall so your v6 connections are wide open to the world. Be careful.
 

Latest threads

Sign Up For SNBForums Daily Digest

Get an update of what's new every day delivered to your mailbox. Sign up here!
Top