I am currently facing an issue with Ethernet over IPv6 (EoIPv6) in RouterOS v7.12.
My goal is to connect LANs at different sites using EoIPv6 interfaces bridged together, aiming for communication with an MTU of 1500.
However, I am encountering unexpected limitations.
RouterOS version: v7.12
Configuration: LANs at multiple sites connected via EoIPv6 interfaces, bridged for inter-site communication.
MTU: 1500
When conducting ICMP measurements between sites, I found that the maximum packet size that could be transmitted without fragmentation was only 1416 bytes.
This suggests an effective MTU of 1444, considering the EoIPv6 overhead.
This is significantly lower than the expected 1500 bytes and is impacting our network performance.
Are there known issues or limitations with EoIPv6 in RouterOS v7.12 that could be causing this MTU size limitation?
What additional steps can I take to diagnose and resolve this issue to achieve the desired MTU of 1500?
Any advice or guidance would be greatly appreciated. Thank you in advance for your assistance.
The tunnel MTU should be set to 1500 to allow the transport full-sized Ethernet frames over the tunnel. As the tunnel overheads [40 (IPv6) + 8 (GRE) + 14 (ethernet) + some amount for IPsec (depends on settings)] will result in a total packet size greater than your WAN MTU it will be fragmented.
IPv6 fragmentation has to be carried out by the endpoints, unlike IPv4 where intermediate routers can fragment packets if the size exceeds the MTU of an onward path, however there may still be performance impacts due to out-of-order packet delivery and ressembly. Do you really need L2 connectivity?
The reason we require L2VPN is to affordably create redundancy in our BGP connections.
We primarily communicate over a dedicated line, but we’re considering scenarios like rare disasters where it might become unavailable.
We’d like to use L2VPN over a shared line provided by a private ISP.
To use it seamlessly, without any noticeable changes, we need to transmit Ethernet frames with an MTU of 1500, just like we do over the dedicated line.
I’ve attached some images, though I’m not sure if they will help find a solution…
According to our ping tests, communication between sites with a ‘PacketSize 1500’ works fine.
Our LAN is set up on an experimental network with an MTU of 1500, and we’re not using VLANs.
No firewall settings have been configured.
The eoipv6 interface is manually set to an MTU of 1500.
We have a setup like ‘ether1 — bridge9999 — eoipv6-tunnel9999’ bridged together.
Is there anything else in the settings that I should check?
Screenshots don’t particularly help, an /export of the configuration with any senstive data redacted (serial number, public IP addresses, etc.) shows exactly what you have.
There is bound to be fragmentation over a conventional WAN, so it is a case of finding potentially a combination of tunneling technology which provides the best performance. As you are using RouterOS v7 it may be worth looking at L2TPv3 or VXLAN.
