Unable to route IPv6 traffic

Software SW help
#1

Hi all,

I have got an issue on my Turris router with IPv6 and can’t figure out what is wrong.

My ISP is sending me a /59 prefix with PD. I have assigned a /64 prefix for the LAN interface. I have both SLACC and DHCPv6 enabled on the LAN interface. Below is my config for odhcp.

config dhcp ‘lan’
option interface ‘lan’
option start ‘100’
option limit ‘150’
option leasetime ‘43200’
list dhcp_option ‘6,192.168.0.1’
option ra ‘server’
option dhcpv6 ‘server’
list ra_flags ‘managed-config’
list ra_flags ‘other-config’

Here you can also see that PD is working properly.

Screenshot 2023-11-02 at 21.12.21
Screenshot 2023-11-02 at 21.12.211908×746 199 KB

On the client I am getting an IP address and the Turris as a default gateway assigned. However, I am unable to ping any destination on the internet. The router responds back to the client with “destination unreachable, unreachable route”.

21:07:05.119094 IP6 (flowlabel 0x7104f, hlim 64, next-header ICMPv6 (58) payload length: 64) 2a02:908:822:ffe5::99 > 2a02:908:822:ffe5:d952:a625:12bb:da85: [icmp6 sum ok] ICMP6, destination unreachable, unreachable route redirector.heise.de

I have done further investigation and believe that the issue can be seen here in the routing table.

root@turris:/tmp/log# ip -6 route
default from 2a02:908:800:2::1297 via fe80::1239:e901:2ca9:5f70 dev eth2 proto static metric 512 pref medium
default from 2a02:908:822:ffe0::/59 via fe80::1239:e901:2ca9:5f70 dev eth2 proto static metric 512 pref medium
2a02:908:822:ffe5::/64 dev br-lan proto kernel metric 256 expires 6462sec pref medium
2a02:908:822:ffe5::/64 dev br-lan proto static metric 1024 pref medium
unreachable 2a02:908:822:ffe0::/59 dev lo proto static metric 2147483647 pref medium
fe80::/64 dev eth1 proto kernel metric 256 pref medium
fe80::/64 dev br-lan proto kernel metric 256 pref medium
fe80::/64 dev wlan0 proto kernel metric 256 pref medium
fe80::/64 dev wlan1 proto kernel metric 256 pref medium
fe80::/64 dev ztcfwtwnlk proto kernel metric 256 pref medium
fe80::/64 dev eth2 proto kernel metric 256 pref medium

As you can see there is a default route, but at the same time there is another entry for the delegated
prefix listed as unreachable. I have no idea why.

If I add a static route for the host I am trying to ping, it works. Adding a static default route doesn’t work.

Does anything have any hints please on how to troubleshoot this further?

Many thanks,
Martin

#2

do you use PPPoE? Such as

image
image1469×1389 187 KB

#3

No, I am not using PPPoE. Both IPv4 and IPv6 are set to DHCP.

#4

Hey, that is actually a correct behaviour. The router install an unreachable route for the whole delegated prefix so in case part of this prefix is not routed, it will not be send back to the default gateway which would result in a ping-pong on the first mile. This unreachable route is overridden with more specific routes for routed part of the delegated prefix, in your case 2a02:908:822:ffe5::/64.

I don’t see anything wrong with your configuration. It should work like this.

Can you share the wan6 and lan part of /etc/config/network?

1 Like
#5

Hey Ondrej,

Many thanks for the response on this. If this is expected behavior then obviously it can’t be the root cause.

Meanwhile, I have been playing around and got it working. The only thing that I have kind of changed, is to remove mwan3. I had mwan3 installed but NOT configured at all, therefore I doubt it to have been interferring.

I am now able to get our with IPv6 from my LAN and another internal interface on the router.

It’s a bit unfortunate not know what the actual root cause was.

Many thanks for the help anyway.

Kind regards,
Martin

#6

Just got the same issue.
I noticed it yesterday too.
Mwan3 disables wan6 by default.
You need to enable in the Mwan3 settings.

1 Like