[MV_ddwrt19]

Hi all,

can someone please help with the IPV6 issue I'm having. My config:
R7800 with Firmware: DD-WRT v3.0-r38835M kongat (02/18/19)

I've enabled IPV6:
Setup-IPV6: IPVT enable, DHCPv6 with Prefix Delegation
Prefix length: 64
DNSs both blank
MTU default 1452
Dhcp6c custom, Dhcp6s, Radvd - disabled

Services-Dnsmasq:
Dnsmasq - enabled
Cache DNSSEC data - disabled
Validate DNS Replies (DNSSEC) - disabled
Check unsigned DNS replies - disabled
Local DNS - enabled
No DNS Rebind - enabled
Query DNS in Strict Order - enabled
Add Requestor MAC to DNS Query - disabled

Additional Dnsmasq Options:
local=/local/
expand-hosts
server=2606:4700:4700::1111
server=2606:4700:4700::1001
interface=br0
dhcp-range=::1000,::FFFF,constructor:br0,ra-stateless,12h
dhcp-option=option6:dns-server,[::]
ra-param=br0,10,300
enable-ra

This config get the router and devices on my LAN IPV6 addresses. IPV6 test sites all test ok but in a few minutes the same IPV6 test site report no IPV6 support.

After some research, i found this site: https://rsalveti.wordpress.com/2016/07/27/netgear-r7000-dd-wrt-ipv6-and-the-lack-of-a-stable-gateway/
that talks about this exact behaviour.

So, I SSH and check ip -6 route and when IPV6 is working I see that the default route is there:
default via fe80::29e:1eff:fe59:9022 dev eth0 metric 1024 expires 170sec

But then, in a few minutes the default route drops and ip -6 route becomes this:
2601:586:c403:1722::/64 dev br0 metric 256
fe80::/64 dev br0 metric 256
fe80::/64 dev eth1 metric 256
fe80::/64 dev ath0 metric 256
fe80::/64 dev ath1 metric 256
fe80::/64 dev ath1.1 metric 256
fe80::/64 dev eth0 metric 256
unreachable default dev lo metric -1 error -101
ff00::/8 dev br0 metric 256
ff00::/8 dev eth1 metric 256
ff00::/8 dev ath0 metric 256
ff00::/8 dev ath1 metric 256
ff00::/8 dev ath1.1 metric 256
ff00::/8 dev eth0 metric 256
unreachable default dev lo metric -1 error -101

From the site I mentioned, I run this to determine if my ISP (Comcast) broadcasts the default route:
tcpdump -vvvv -ttt -i eth0 icmp6 and 'ip6[40] >= 133 && ip6[40] <= 134'

which in a second comes up with this:
00:00:03.132041 IP6 (class 0xe0, hlim 255, next-header ICMPv6 (5 payload length: 160) fe80::29e:1eff:fe59:9022 > ff02::1: [icmp6 sum ok] ICMP6, router advertisement, length 160
hop limit 64, Flags [managed, other stateful], pref medium, router lifetime 1800s, reachable time 3600000s, retrans time 0s
source link-address option (1), length 8 (1): 00:9e:1e:59:90:22
0x0000: 009e 1e59 9022
mtu option (5), length 8 (1): 1500
0x0000: 0000 0000 05dc
prefix info option (3), length 32 (4): 2001:558:40c0:80::/64, Flags [none], valid time 604800s, pref. time 302400s
0x0000: 4000 0009 3a80 0004 9d40 0000 0000 2001
0x0010: 0558 40c0 0080 0000 0000 0000 0000
prefix info option (3), length 32 (4): 2001:558:5014:84::/64, Flags [none], valid time 604800s, pref. time 302400s
0x0000: 4000 0009 3a80 0004 9d40 0000 0000 2001
0x0010: 0558 5014 0084 0000 0000 0000 0000
prefix info option (3), length 32 (4): 2001:558:6030:7a::/64, Flags [none], valid time 604800s, pref. time 302400s
0x0000: 4000 0009 3a80 0004 9d40 0000 0000 2001
0x0010: 0558 6030 007a 0000 0000 0000 0000
prefix info option (3), length 32 (4): 2001:558:801e:88::/64, Flags [none], valid time 604800s, pref. time 302400s
0x0000: 4000 0009 3a80 0004 9d40 0000 0000 2001
0x0010: 0558 801e 0088 0000 0000 0000 0000

So, the broadcast is there! Also, as soon as I run this command, the default route re-appears in ip -6 route and IPV6 works again. But, after a few minutes stops.

For now, I added the default route manually but that's not a good solution as its IP might change.

Can anyone help determining why the IPV6 default route drops?

[MV_ddwrt19]

All needed for this issue to be resolved was to disable (uncheck) "Filter Multicast" on Security/Firewall page

[mac913]

Incase IPv6 stops working...

I ran into the same problem,read my Post...
https://forum.dd-wrt.com/phpBB2/viewtopic.php?t=313047&start=2&highlight=r7800+rdisc6

More likely you need the "rdisc6" file, like the site you found, read the whole article again. I have attached the file just unzip it.

Since the article was written for an R7000 the WAN port is vlan2. My cron runs every 15min on the R7800...

*/15 * * * * root /your-directory/rdisc6 -1 -q eth0

[stalonge]

[HalfBit]

[mac913]