Posted: Sat Mar 14, 2020 22:21 Post subject: [Solved] R7000 Comcast IPv6 cannot ping out to internet
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)
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.
Joined: 08 May 2018 Posts: 14125 Location: Texas, USA
Posted: Sun Mar 15, 2020 5:36 Post subject:
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. _________________ "Life is but a fleeting moment, a vapor that vanishes quickly; All is vanity"
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Linux User #377467 counter.li.org / linuxcounter.net
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