[Solved] R7000 Comcast IPv6 cannot ping out to internet

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fatalhalt
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Joined: 29 Oct 2015
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PostPosted: Sat Mar 14, 2020 22:21    Post subject: [Solved] R7000 Comcast IPv6 cannot ping out to internet Reply with quote
Hi guys, I have a really painful IPv6 issue where I cannot ping out nor access any ipv6 host on the internet. This problem always happens after I reboot my R7000, the issue usually fixes itself overnight but so far I have been waiting more than 12h and ipv6 is still is blocked.

The dhcp6c is working correctly, the 2607:* PD prefix has been acquired and assigned to router's br0/vlan2. radvd is working correctly, all of the hosts on my 192.168.1.0/24 subnet have been assigned an ipv6 address and all are accessible/pingable via ipv6 locally, however none can reach out to internet via ipv6.

Looking at "tcpdump -i vlan2 "icmp6 && ip6[40] == 128", I can see icmp6 echo requests coming out from vlan2 to internet when pinging ipv6.google.com, I don't see an echo-reply anywhere, however 'watch -n1 ip6tables -nvL" in INPUT chain I can see icmpv6 pkt count growing, so echo replies are being sent but something in ddwrt is discarding them:
root@R7000:~# ip6tables -nvL
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
56 10076 ACCEPT 0 * * ::/0 ::/0 state RELATED,ESTABLISHED
2111 250K ACCEPT icmpv6 * * ::/0 ::/0 (count keeps growing whenever I'm pinging)

root@R7000:~# ping6 ipv6.google.com (terminal 1)
PING ipv6.google.com (2607:f8b0:4009:813::200e): 56 data bytes
^C
--- ipv6.google.com ping statistics ---
6 packets transmitted, 0 packets received, 100% packet loss

root@R7000:~# tcpdump -i vlan2 "icmp6 && ip6[40] == 128" (terminal 2)
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on vlan2, link-type EN10MB (Ethernet), capture size 262144 bytes

16:57:32.001696 IP6 2601:999:9999:9999:200:ff:fe00:0 > iad23s59-in-x0e.1e100.net: ICMP6, echo request, seq 0, length 64
16:57:33.006306 IP6 2601:999:9999:9999:200:ff:fe00:0 > iad23s59-in-x0e.1e100.net: ICMP6, echo request, seq 1, length 64
16:57:34.015854 IP6 2601:999:9999:9999:200:ff:fe00:0 > iad23s59-in-x0e.1e100.net: ICMP6, echo request, seq 2, length 64
16:57:35.025399 IP6 2601:999:9999:9999:200:ff:fe00:0 > iad23s59-in-x0e.1e100.net: ICMP6, echo request, seq 3, length 64
16:57:36.027875 IP6 2601:999:9999:9999:200:ff:fe00:0 > iad23s59-in-x0e.1e100.net: ICMP6, echo request, seq 4, length 64

root@R7000:~# uname -a
Linux R7000 4.4.213 #867 SMP Thu Feb 6 21:24:35 +04 2020 armv7l DD-WRT
root@R7000:~# ps | grep dvd
9366 root radvd -C /tmp/radvd.conf
9367 root radvd -C /tmp/radvd.conf
10529 root grep dvd
root@R7000:~# ps | grep dhcp
9114 root dhcp6c -c /tmp/dhcp6c.conf -T LL vlan2
9362 root udhcpc -i vlan2 -p /var/run/udhcpc.pid -s /tmp/udhcpc -O routes -O msstaticroutes -O staticroutes
10532 root grep dhcp
root@R7000:~# ifconfig | head -n9
br0 Link encap:Ethernet HWaddr FF:FF:FF:FF:FF:FF
inet addr:192.168.1.1 Bcast:192.168.1.255 Mask:255.255.255.0
inet6 addr: fe80::deef:9ff:fe97:2219/64 Scope:Link
inet6 addr: 2601:999:9999:9999:200:ff:fe00:0/64 Scope:Global
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:394658 errors:0 dropped:42873 overruns:0 frame:0
TX packets:227387 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:42185328 (40.2 MiB) TX bytes:104484778 (99.6 MiB)

I tried clearing "ip6tables -F" ipv6 rules but no help, problem doesn't lie there.



Screenshot from 2020-03-14 17-21-57.png
 Description:
DHCPv6 with PD
 Filesize:  74.75 KB
 Viewed:  2329 Time(s)

Screenshot from 2020-03-14 17-21-57.png




Last edited by fatalhalt on Sun Mar 15, 2020 17:41; edited 1 time in total
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kernel-panic69
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PostPosted: Sat Mar 14, 2020 23:59    Post subject: Reply with quote
Which build revision are you using?
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fatalhalt
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Joined: 29 Oct 2015
Posts: 39

PostPosted: Sun Mar 15, 2020 4:41    Post subject: Reply with quote
kernel-panic69 wrote:
Which build revision are you using?
I was on Feb 08 build when I wrote the post, now I'm on v3.0-r42681 std (03/13/20). I had this problem since I first learned how to setup IPv6 on DD-WRT, might have been couple years, I was on Kong's R7000 builds when he used to be active, also had the problem back then.
kernel-panic69
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Joined: 08 May 2018
Posts: 14125
Location: Texas, USA

PostPosted: Sun Mar 15, 2020 5:36    Post subject: Reply with quote
I personally don't use ipv6. Everything this side of the ISP router only uses ipv4. Maybe PerYngveBerg or one of the knowledgeable guys with ipv6 on DD will swing by and chime in.
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fatalhalt
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Joined: 29 Oct 2015
Posts: 39

PostPosted: Sun Mar 15, 2020 8:22    Post subject: Reply with quote
thanks @kernel-panic69, I use IPv6 all the time, no way I will disable it, besides it is 2020.

I have fixed the problem! Comcast was was dropping my IPv6 traffic upstream. Power cycling the modem was the answer. Big thanks to @roadrun777 in this post: https://forum.dd-wrt.com/phpBB2/viewtopic.php?p=1166167&highlight=#1166167 for the clues.

roadrun777 wrote:
Comcast sometimes likes to disable ipv6 routes, it is probably due to a time limit on the lease not corresponding to the ipv4 side, as I have lost ipv6 routing for no reason other than upstream not accepting anymore. So a cable modem power cycle usually fixes the issue.


During my research I also learned about 3 infamous DDWRT IPv6 hotfixes/workarounds (none were needed for me), I'm just mentioning it here for documentation.
-run ifconfig eth0 promisc
-Services->Dnsmasq, check "Add Requestor MAC to DNS Query"
-(uncheck) "Filter Multicast" on Security/Firewall page
kernel-panic69
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Posts: 14125
Location: Texas, USA

PostPosted: Sun Mar 15, 2020 9:52    Post subject: Reply with quote
Good to hear you got it sorted. Please edit OP topic to include [SOLVED].
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