I have been allocated a /56 IPV6 from my ISP. I have DHCPv6 setup on the pppoe0 interface (PPPoE over VDSL2) and a /64 from the pool on the LAN interface (Vlan40).

When I use address auto config, it works fine.

When I try to set a static IP on the host and Vlan40, it works for a few minutes to an hour (aprox) and then refuses to work via IPV6. At that point I can't even ping the router IPV6 LAN address.

Additionally, "route -A inet6" on the client (Linux desktop) shows all the route entries are still there.

I have tried disabling both auto config and then ND and this does not fix the issue.

Post here config of IPv6 - Address. IPv6 - ND. IPv6 - Neighbors.

I have been allocated a /56 IPV6 from my ISP...

Michael,

are you using Dt. Telekom? You must take care on the dynamic IPv6 prefix change (Zwangstrennung). It's better to internally address via ULA address. Also you must decrease the GUA lifetime by hand as RouterOS does not care about the lifetime given by DHVP6.

Here is a working configuration for Dt.Telekom/Versatel which also make DNS working:

Prior to doing this I reinstated auto config and ND.

IPV6 / Addresses
[admin@MikroTik] /ipv6 address> print
Flags: X - disabled, I - invalid, D - dynamic, G - global, L - link-local
# ADDRESS FROM-POOL INTERFACE ADVERTISE
0 DL fe80::dceb:95ff:fe38:7658/64 bridge-wlan no
1 DL fe80::1c37:82ff:fe40:ebb5/64 bridge1 no
2 DL fe80::ce2d:e0ff:fe8c:92d1/64 vlan10 no
3 DL fe80::ce2d:e0ff:fe8c:92d1/64 sfp1 no
4 DL fe80::ce2d:e0ff:fe8c:92d0/64 vlan50 no
5 DL fe80::ce2d:e0ff:fe8c:92d0/64 vlan40 no
6 DL fe80::a/64 dialer0 no
7 G [network redacted]::1/64 ipv6-pool vlan40 yes
[admin@MikroTik] /ipv6 address>

IPV6 / ND
[admin@MikroTik] /ipv6 nd> print
Flags: X - disabled, I - invalid, * - default
0 * interface=all ra-interval=3m20s-10m ra-delay=3s mtu=unspecified reachable-time=unspecified retransmit-interval=unspecified
ra-lifetime=30m hop-limit=unspecified advertise-mac-address=yes advertise-dns=no managed-address-configuration=no
other-configuration=no
[admin@MikroTik] /ipv6 nd>

I set the Vlan40 address as [network]::1/64 and the host address as [network]::2/64

are you using Dt. Telekom? You must take care on the dynamic IPv6 prefix change (Zwangstrennung). It's better to internally address via ULA address. Also you must decrease the GUA lifetime by hand as RouterOS does not care about the lifetime given by DHVP6.

Thanks for that. I am a customer of InspireNet in New Zealand and the /56 block is dedicated to my account.
Based on my understanding of what you are saying, it appears no change is necessary at my end as the IP addresses are consistent.
I have manually specified Google's IPV6 DNS servers on the client host.

I have fixed the issue by doing both of the following:
1. Disabling auto-addressing on the relevant VLAN
2. Disabling Slackware NetworkManager and setting my IP address manually in rc.inet1 (IPV4) and rc.local (IPV6) as follows:

/etc/rc.d/rc.networkmanager stop
chmod 600 /etc/rc.d/rc.networkmanager

/etc/rc.d/rc.local
/sbin/ip -6 addr add [network redacted]::2/64 dev eth0
/sbin/ip -6 route add default via [network redacted]::1 dev eth0