Experiences with ipv6?

RouterOS General
1

Hi,

Some days ago I again experienced some ipv6-troubles with my network. This time, the router rearranged the prefixes it hands out, so my servers again became unavailable over ipv6.

My ISP gave me a /56 prefix. My system has three networks, the prefixes were xx:1900::/64, my main network, xx:1901::/64 and xx::1902::/64, two less important vlans.

After changing the mtu of my ipv6-network the router decided to change the prefix of the main network to xx::1903::/64, after reverting the mtu, it changed the prefix to xx::1904::/64. So my servers became unavailable over ipv6. That was more than two weeks ago.
Now, for some reason, the router decided to rearrange the prefixes. Now the lesser important networks got xx:1900::/64 and xx::1901::/64. The main network got xx::1902::/64. Again my servers became unavailable over ipv6.

Anyone having similar experiences with ipv6 ?
Can I tell the router which prefixes it should hand out ? Of course based on the prefixes the ISP gives.

Thanks.

2

Is it static or dynamic?

If it's dynamic, everything else must be too...

Ask your ISP for a static block and then create subnets as you like.

3

Yes, the issue with the interface getting new prefix from the pool with every modification is a long standing one.

Good news, however, is that in 7.21 this annoying behavior will finally be addressed:

  • ippool6 - take into account "subnet-id" when specified on address;

Here you can see it working fine:

image
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Here a7 is the subnet-id (8 available bits with a /56 prefix) that you can hardcode in the address entry. With a /60 pool then of course you can only choose 4 bits.

4

What is dynamic ? I’m with the same isp for years. Only when I changed from vdsl to fiber I got a new prefix. And that’s probable because I changed routers, from fritzbox to mikrotik.

I understand that my prefix could change, but it didn’t. Nevertheless, the router shuffled the “internal” prefixes.

5

Oh, good to know, I’ll be watching this.

Thanks.

6

Does it work also if prefix falls into "upper part" of the /56 ? E.g. not fd5e:6379:994a:0000::/56 but fd5e:6379:994a:5900::/56 ? It used to work for the former case already in ROS v6 ... but not for the later case. The problem was that ROS took the prefix from pool as a whole (including the 00 from part 5900 which is not part of /56 prefix) and the "subnet id" as well ... and couldn't combine them intelligently (i.e. to 59a7). With "bottom part" (all zeroes) it successfully formed e.g. 00a7 ...

When rrported, they claimed it wasn't bug report but rather feature request ... so I wonder if they finally came around to do/fix it.

7

It seems to work:

image
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And the ability to have the preferred subnet-id is really new in 7.21. With <= 7.20.4 attempts like above resulted in this:

image

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