[NightshadeinSF]

I have done this exact style of setup so many times, but for some reason I cannot get it to work and its driving me nuts.

Heres the deal. I live with 3 housemates. One housemate has Comcast Cable Internet Service. His comcast cable modem is at 10.0.0.1/24. This subnet is also reachable via WIFI and the other housemates get connect their devices that way.

In my room, I have a home lab with 8 Supermicro Servers, a notebook, a desktop, and an ASUS RT-AC88U router running DD-WRT. My lab is on 10.0.2.0/24. The WAN port on my ASUS router is hooked into the Comcast Cable Modem 10.0.0.0/24 Subnet.

This exact setup has worked for almost 2 years. I recently updated to a newer version of DD-WRT and I cant seem to get it working again. Its not the update, because after an hour or two I went back to the previous version of DD-WRT that had been working for 2 years and I still could not get it working. Other than the update, nothing else has changed.

How should I configure my router so my packets are routed properly to the internet? Also, just FYI DHCP and DNS are provided by a Windows Server instance running on my vmware server, so neither of those have to be configured on my DDWRT router...

I am grateful for any help. I literally have made this work at least 25 times before on my network and on others... I am not sure why I am getting stumped by this config now.

Thanks,
Nightshade

[egc]

The only thing you have to do is to reset the router to defaults and connect its WAN port to the comcast.

Do not restore settings just test as is.

For testing do not connect your Windows server with the DHCP/DNS and just see if you have internet from your router.

[NightshadeinSF]

I also disconnected everything on my homelab network except one notebook and allowed it to get IP settings via DHCP from the DDWRT router after it was restored to defaults. I received an IP. I am able to ping the Comcast Subnet just fine and the Comcast Router. I am able to resolve DNS names to IP address via the DNS settings acquired via DHCP. I cannot reach the internet however. If I try to ping 8.8.8.8 or any other known internet IP address the ping fails.

Any other suggestions? This seems to be a step in the right direction but something is still keeping me from being routed correctly...

Thanks,
Nightshade

[egc]

Did you try to ping and traceroute from your router?

Did you check your router is on its default 192.168.1.1/24 subnet and the WAN of the router is 10.0.0.x

What if you connect your laptop directly to the comcast via the same cable as you use for your router?

[NightshadeinSF]

In the beginning, I mentioned that the only change in configuration was me upgrading to a new DDWRT version and then rolling back to the original version. As it turns out, that was not correct.

When I connected my laptop to the cable that is pluggin into the WAN port on my homelab subnet, it worked just fine. NSlookup, connecting to web pages, everything worked. However, when I ran Get-NetIPAddress in windows I noticed that in addition to an IP4 Address, my notebook also had IP6 address configured. On my subnet, I don't use IP6 just because thus far I have not had a reason to. Just for kicks, I disabled IP6 on my notebooks wired network adapter. Low and behold, there was no longer internet connectivity. I could still see the Comcast subnet via their IP4 addresses, but I could no longer reach the internet, not even if I pinged an internet IPv4 address.

Does this mean the comcast router is setup to only route IPv6? Would this be intentional or a setting someone turned on by accident? The housemate who has the Comcast service has no idea why this would happen. While not a dummy, I would be extremely surprised if he could explain to someone the benefits or lack there of of having a router than would only route IP6 and not IP4.

Lets assume for the moment that this Comcast configuration is fixed, what would I have to do? Enable IPv6 on DDWRT and just paste in the IP6 address the Comcast router has? Would this router have IP6 DHCP. While I have several years of configuring networking on Windows machines with IP4, I have only extremely basic knowledge of IP6. I can find an "Intro to IP6" webpage myself, but just for the record, is there anything IP6 related I should know with regards to DDWRT. Last Question: Any chance this is some strange coincidence and the problem is not related to IP6?

Thank you for your help. Thank you Thank you!

Nightshade

[egc]

Interesting, maybe Comcast ran out of IP4 addresses and is now only using IPv6 ?

Does not sound very plausible but who knows.

I just started with IPv6 myself so cannot help you very much.

Normally the router needs a delegated prefix which you can work with but the Comcast router probably does not hand out that.
Without that you can do two things i can think of:

Use the router as a Wireless Acces Point, so all clients will get a Global Unicast Address ( https://www.networkworld.com/article/3235384/ipv6-address-enterprises-how-to-easier-than-ipv4.html ) from Comcast and have internet and are reachable via IPv6 or you can use NAT66 to make your own IPv6 subnet and NAT via your router.

But I would research first what is happening with the Comcast router, hardly believe it is IPv6 only, maybe someone messed with the settings?

[SurprisedItWorks]

FWIW, I have a family member's Linksys WRT1900ACSv2 on dd-wrt 50474 connected just as in your setup. It's a housemate situation, with the dd-wrt router's WAN connected to a LAN port on a primary router connected to Comcast. Until recently ipleak.net always showed only an IPv6 address for that Comcast router, even though there is nothing special about the dd-wrt setup to deal with IPv6. I keep IPv6 disabled in dd-wrt and run strictly IPv4. The dd-wrt WAN uses a standard IPv4 DHCP setup and has always ended up assigned a 10.0.0.X address by the Comcast router. I never had to think about the Comcast setup at all. Everything just worked.

More recently I'm seeing an IPv4 address on ipleak.net for the Comcast WAN. Perhaps someone changed some configuration on the Comcast router? But we never lost dd-wrt functioning. Presumably the Comcast router was wrapping our IPv4 packets in IPv6 "envelopes" to send on to their servers. Who knows? But I cannot really imagine a serious ISP, even one as infuriating as Comcast, simply refusing to handle IPv4, one way or another. There's just too much of it out there.