Switched to AT&T fiber, IPv6 tunnel broken

[JKnott]

@johnpoz said in Switched to AT&T fiber, IPv6 tunnel broken:

I thought back when they first rolled out ipv6 they were using 6rd and were blocking 41 because they were using it

My ISP was offering 6to4 and 6rd before going native. I had no problem using 6in4, back then. There should have been no conflict with protocol 41.

[JKnott]

@johnpoz said in Switched to AT&T fiber, IPv6 tunnel broken:

I would think putting it into bridge mode would disable any sort of firewalling

Given the firewall in those modems, is that a bad thing?

Since this is a pfSense forum, I expect people here will be running pfSense for their firewall.

[johnpoz]

@JKnott said in Switched to AT&T fiber, IPv6 tunnel broken:

There should have been no conflict with protocol 41.

I agree - just what I read some places, doesn't mean its true. Some thread somehwere was stated that att was blocking protocol 41 for anything other than their network, and when they moved to dual stack vs 6rd for their IPv6 rollout they remove the 41 block.

I am leaning towards the disable ipv6 in his att device to be honest, since if you are using the device as passthru and wanted to disable IPv6 blocking protocol 41 would be a way to stop a client connected from creating a tunnel and using IPv6 that way, etc.

[BiloxiGeek]

Is there a difference between bridge mode and passthrough? I've set passthrough already and didn't get the tunnel up. If there's a separate bridge mode I'm more than willing to give it a try but I've not seen that setting anywhere in the BGW320 config.

And I too would prefer to deal with any latency issues in order to keep the 6in4 tunnel with the known and expected addresses.

[johnpoz]

@BiloxiGeek that might what its called on that device, can you enable IPv6 and leave it passthru?

[marcg]

@johnpoz There's no true bridge mode on the BGW320 AFAIK. IP Passthrough is bridge-like, but is NAT under the hood. With Passthrough enabled and v6 disabled on the BGW LAN side, I could see how that might prevent ATT's native v6 from working. Disabling v6 might prevent the Passthrough v6 NAT states from being created.

@BiloxiGeek, if you haven't already done so, suggest that the BGW's Passthrough Mode be configured as DHCPS-Fixed with the pfSense WAN MAC entered as the Passthrough Fixed MAC Address. If there's ever more than one device on the BGW's LAN side -- wired or wireless -- at boot time, the DHCPS-Dynamic option will cause the BGW to pick whichever device it sees first as the passthrough client, not necessarily pfSense (probably not what you want).

[johnpoz]

@marcg said in Switched to AT&T fiber, IPv6 tunnel broken:

isabling v6 might prevent the Passthrough v6 NAT states from being created.

concur - I do believe that is his problem.. I don't think those devices do a true bridge, more like a nat with with dmz host sort of thing.

[marcg]

@johnpoz said in Switched to AT&T fiber, IPv6 tunnel broken:

I don't think those devices do a true bridge, more like a nat with with dmz host sort of thing.

It's similar, but different. In Passthrough mode, pfSense gets the public v4 IP of the BGW. For v6, the pfSense gets a routeable IP via DHCP for its WAN IP, and any delegated prefixes that it requests. pfSense thinks that it's directly on the WAN with routeable addresses and prefixes.

The BGW then 1:1 NATs every flow to/from pfSense, keeping the same source/destination address/port on both sides of the NAT. There's a snippet from the BGW's NAT table below. The x's are to obscure my routeable addresses and prefixes.

Guessing one reason they don't do a true bridge is to enable the BGW to NAT+route in parallel for its non-Passthrough LAN-side clients (none in my case).

[johnpoz]

@marcg well that is good, then it should work for the OP.

[BiloxiGeek]

Ran a traceroute yesterday,

[25.07.1-RELEASE][root@firewall]/root: traceroute -P 41 184.1.1.1
traceroute to 184.1.1.1 (184.1.1.1), 64 hops max, 40 byte packets
 1  dsldevice.attlocal.net (192.168.1.254)  0.574 ms  0.472 ms  0.469 ms
 2  * * *
 3  * * *
 4  * * *
 5  * * *
 6  192.205.32.138 (192.205.32.138)  14.657 ms  15.537 ms *
 7  * * *

A separate run on that showed a different path but at a similar point I got a response from something and then nothing else.

One solution that I keep seeing during my searching is to switch to a business account. Just got a basic price list for that and it's flat out ridiculous. Over a thousand dollars a month to be provisioned at 1Gbps and no idea if I'd still see this problem or not.

[johnpoz]

@BiloxiGeek said in Switched to AT&T fiber, IPv6 tunnel broken:

traceroute -P 41 184.1.1.1

Protocol 41 is not a port.. Traceroute support tcp and udp I don't think that is going to work.

[BiloxiGeek]

@johnpoz I was given the impression that the traceroute on a pfSense box can use the -P 41 to test protocols. But I will dig into it deeper once I get home from work to doublecheck.

[johnpoz]

@BiloxiGeek yeah it is possible to do raw and specific protocol - but not sure 41 is an option.. But that might depend on what version of traceroute, etc. I think you can do such things with hping3 as well.. But not sure of all protocols that you can do, etc.

Just wanted to let you know that might want to verify it was doing what you expected it to be doing before you think its reporting a clear failure, etc.

[BiloxiGeek]

@johnpoz I'm gonna setup a linode nanode this afternoon to do some testing from outside AT&T's sphere of influence. See if I can get a better idea of where the 6in4 packets are being dropped.

I did find this a bit ago:
nmap -6 -sO -p 41 <ip>

(That's a capital letter O.)

That appears to probe for protocol 41 specifically. I have to test when I get home to see if I should be testing to the v4 address or the v6. (or both)

[johnpoz]

@BiloxiGeek this is what I get, which I do have he tunnel up.

Starting Nmap 7.97 ( https://nmap.org ) at 2025-09-04 13:56 -0500
Nmap scan report for tserv9.chi1.ipv6.he.net (184.105.253.14)
Host is up (0.010s latency).

PROTOCOL STATE         SERVICE
41       open|filtered ipv6

Nmap done: 1 IP address (1 host up) scanned in 0.44 seconds

You do understand you should be checking to your HE tunnel IPv4 address for the tunnel endpoint you are using.. For example you see above I am using the chi pop for HE at that 184.105.254.14 address

[marcg]

Here's what I see with a BGW320 in Passthrough mode using ATT's native v4/v6 services. No HE tunnel running.

Testing was done from an Ubuntu machine behind pfSense to the HE POP address provided by @johnpoz . First hop is pfSense, second hop is the BGW, and the packet makes it to HE no later than hop 8.

prompt# traceroute -P 41 184.105.254.14
traceroute to 184.105.254.14 (184.105.254.14), 30 hops max, 60 byte packets
 1  pfSense.home.arpa (192.168.15.1)  0.136 ms  0.080 ms  0.080 ms
 2  192.168.1.254 (192.168.1.254)  0.700 ms  0.373 ms  0.398 ms
 3  * * *
 4  * * *
 5  * * *
 6  * * *
 7  * * *
 8  e0-35.switch1.sjc2.he.net (64.62.171.65)  4.678 ms  5.896 ms  3.869 ms
 9  * * *
10  * * *
11  * * *

[johnpoz]

@marcg yeah I don't think that traceroute will work. What does your nmap test show

edit:
You know I don't even think the nmap test is valid.. I picked another tunnel endpoint so not to mess with with current tunnel I have open.. And when I sniff on pfsense wan and do another nmap.. I see nmap send what appears like protocol 41, but get no answer and lists as invalid.. Did it actually go out the wire?? and just not get an answer.. Or did it not really go out the wire and just caught in the packet capture.

15:10:57.645055 IP 209.snipped > 184.105.253.10: IP6  [length 0 < 40] (invalid)
15:10:57.806265 IP 209.snipped> 184.105.253.10: IP6  [length 0 < 40] (invalid)

184.105.253.10 is their dallas pop tserv8.dal1.ipv6.he.net

If I sniff the previous IP where I do have a tunnel open... I see responses.

So I am not sure there is a way to test if 41 is open with nmap or traceroute..

but since @marcg is using the same device and also on att and can open a tunnel - this shows that at least where he is at they are not filtering.. Why would they filter it some locations but not all?

[marcg]

@johnpoz said in Switched to AT&T fiber, IPv6 tunnel broken:

@marcg yeah I don't think that traceroute will work. What does your nmap test show

The traceroute showed that Protocol 41, IPv6, makes it through the ATT network to HE (with no HE tunnel up).

Similarly, from a LAN host, nmap shows he.net is reachable over v6.

prompt# nmap -6  -sO -p 41  tserv9.chi1.ipv6.he.net
Starting Nmap 7.80 ( https://nmap.org ) at 2025-09-04 13:30 PDT
Nmap scan report for tserv9.chi1.ipv6.he.net (2001:470:0:6e::2)
Host is up (0.049s latency).
Other addresses for tserv9.chi1.ipv6.he.net (not scanned): 184.105.253.14
rDNS record for 2001:470:0:6e::2: tserv1.chi1.he.net

PROTOCOL STATE         SERVICE
41       open|filtered ipv6

It'd be helpful if the OP left the BGW's IP Passthrough up, re-enabled IPv6 on its LAN side, and repeated these tests from their machine. As you suggested earlier, disabling LAN side IPv6 on the BGW could be the cause of the problem. Testing that is simpler -- a few mouse clicks -- than any other testing we're doing in this thread.

[JonathanLee]

@BiloxiGeek do you have a static ipv4? I pay extra for a static address it helps because my tunnel ipv4 address stays the same and my vpn also.

[JKnott]

@marcg said in Switched to AT&T fiber, IPv6 tunnel broken:

prompt# nmap -6 -sO -p 41 tserv9.chi1.ipv6.he.net

-p is port, not protocol.

6in4 is protocol 41. It is not UDP (17) or TCP (6). You'd use the port number as part of a UDP or TCP packet, not 6in4.