V6 ULA unreachable from client until ping from router

Installing and Using OpenWrt
1

Hello,

I run an unbound recursive dns server on my router. It listens on ULA addressing starting with fd3. For some reason my servers can't reach the dns server running on the router until I ssh into the router and ping the server's ULA address. Then pings from the server to your router start working almost instantly.

Some of the servers start taking a really long time to to get addressing via SLAAC on te order of several minutes. This used to be instant. It is now also happening with some of the hosts on the LAN.

There is a Neatgear S350 Series 8-Port Gigabit Ethernet Smart Managed Pro Switch and a Mikrotik CRS125-24G-1S-2HnD between the router and the the servers. The servers are a FreeBSD host running vnet iocage jails. The links between the router and the netgear, as well as between the netgear and the mikrotik are configured as vlan trunk lines, with the servers on it's own separate vlan. Spanning Tree Protocol is enabled on all networking devices, the router and switches. Multicast is enabled on the netgear switch.

NAME="OpenWrt"
VERSION="22.03.3"
ID="openwrt"
ID_LIKE="lede openwrt"
PRETTY_NAME="OpenWrt 22.03.3"
VERSION_ID="22.03.3"
HOME_URL="https://openwrt.org/"
BUG_URL="https://bugs.openwrt.org/"
SUPPORT_URL="https://forum.openwrt.org/"
BUILD_ID="r20028-43d71ad93e"
OPENWRT_BOARD="ramips/mt7621"
OPENWRT_ARCH="mipsel_24kc"
OPENWRT_TAINTS=""
OPENWRT_DEVICE_MANUFACTURER="OpenWrt"
OPENWRT_DEVICE_MANUFACTURER_URL="https://openwrt.org/"
OPENWRT_DEVICE_PRODUCT="Generic"
OPENWRT_DEVICE_REVISION="v0"
OPENWRT_RELEASE="OpenWrt 22.03.3 r20028-43d71ad93e"

2

Still having this issue and haven't found out what's causing it.

3

Maybe this issue is with these devices?

4

I disabled IGMP snooping on all devices since after some reading it is for IPv4 only which I don't really use. I left 'multicast enable' in the openwrt's bridge settings but turned igmp snooping and querirer off. Going to do some testing with this.

5

Maybe this issue is with these devices?

I wouldn't know how to test this theory.

6

Having a look into the vendor manuals for hints. It also helps to glimpse over the release notes of their firmware and look out for this issue or other IPv6 related one.
Maybe it's a "security" feature that some IPv6 multicast packets got eaten up or not properly processed.

If you have enough laptops/PCs I would connect one at each switch and the router and run tcpdump to look what packets got over the wire and which packets don't show up at the other end. Yes I know these kind of issues suck :confused: