Bug: RouterOS beta 7.1beta4 - RFC3021 - does not route out on a /31 - but accepts traffic from a /31

Bug: RouterOS beta 7.1beta4 - RFC3021 - does not route out on a /31 - but accepts traffic from a /31

I heard rumours on RouterOS v7 will support RFC3021, which is great. Comparing to v6, it will atleast accept traffic from a /31 IP.

Ping from “north” with source address 10.0.2.3

  • Can ping 10.0.2.2
  • Can ping 192.168.5.1
  • Packet reaches 192.168.5.2. South replies, but reply gets stuck on its way back - at west router

Ping from “north” with source address loopback 172.16.1.1

  • Packet leaves “north” router
  • Can not ping 10.0.2.2, as west never replies to ICMP
  • “west” has an Active route to 172.16.1.1… /ip route add dst-address=172.16.1.1/32 gateway=10.0.2.3

Ping from “south” with source address 192.168.5.2

  • Can obviously ping 192.168.5.1
  • Can ping 10.0.2.2
  • Can not ping 10.0.2.3 (traffic is never sent out on west ether2)



    I have this simple topology

/31 is officially unsupported.

Can you support it in v7 please? :slight_smile: Since it’s supported (works) one way already :slight_smile:

Yes, we would like to see this and /127 supported as well. MikroTik says no need because we have /32 but /31 and /127 are so standard in terms of router support, it makes MikroTik seem like the odd ones out if they do not support it.

/127 is different topic (completely unrelated to RFC3021), and BTW /127 is suppoerted and works in ROSv7

It is great that /127 is supported, I assumed it would be in the same boat as /31. I did know they are separate RfC’s but they have a similar purpose, so I wouldn’t say it is “completely unrelated”. Or are you saying that the Linux kernel somehow does not support /31 but supports /127?

Yes, IPv4 and IPv6 stacks in Linux kernel are completely separate.

I think /31 support is important. As much as I push for IPv6, the world is still operating IPv4 and will be for a while. I’ve run into the problem more and more where we have to use Cisco or Juniper due to lack of official /31 support. (many orgs do not want to use the /32 workaround)

MikroTik has quietly added /31 address support to the “v7 Routing Protocol Status” page: https://help.mikrotik.com/docs/display/ROS/v7+Routing+Protocol+Status

Good find. I will upgrade my lab and test beta5

It says that /31 is not supported, so that people stop asking whether /31 is supported or not.

What does this even mean? Are you adding features on the v7 status page just to say it’s not going to be supported?
And why should we stop asking for features that are not supported? Isn’t that the whole point of asking, because we obviously want the feature.

A better answer would be: “yes we aim to add this feature in v7”
Or “no this will never be added because of x or y”

That way we will know if it’s worth investing time in routeros.

In my opinion, the bigger issue is the “fail silently” of a /31 route.

Officialy unsupported to me, means that ROS should activelly refuse a /31 route as invalid.

The current way invites headache as the route is added and people spend time chasing tails.

It says /31 is not supported right now - the fact it is on the list suggests that /31 support is potentially intended for a later release. The red boxes on the left have been turning green as we move further through the v7 beta releases. I assume the point of that page is that when the rightmost boxes are all green, we may be getting closer to a ROS v7 stable release?

Plenty of things don’t support /31 addressing, even Windows being one of them :wink:
While it is useful for PtP links is this really such a huge problem? In my books it’s more “nice to have one day” but there are many more things which should be a priority over /31.

Here’s a big part of the reason - in North America at least, MikroTik is often viewed as a tinkertoy router solution. /31 support is something that any half decent router is expected to support. MikroTik not supporting that just means a lot more “see, told ya so, this MikroTik thing is garbage, they don’t even support /31, Cisco is way better”. It is hard to convince them otherwise when, aside from MikroTik, the only major router vendors that do not support /31 are vendors who make routers that are mainly intended as firewalls, such as Check Point.