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LennonNZ
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/31 not useable on Mikrotik

Sat Jun 30, 2012 4:00 pm

People where talking about /31's not being useable on Mikrotiks quite a while ago.

It is not like they are new in the internet world at all but when I was testing them even on recent software versions /31's would not work.

With IPv4 being in short supply these dating using 2 IP Addresses on a PTP link instead of using 4 ( a /30) does make sense and I would love to know if there is a time frame they will work as nearly every other people of hardware supports /31's..

Why not mikrotik?

Craig
 
oreggin
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Re: /31 not useable on Mikrotik

Sat Jun 30, 2012 11:05 pm

Same thing here, but I don't forcing this because I can live with /30s and IPv6 is coming and knocking on the window :-)
 
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nz_monkey
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Re: /31 not useable on Mikrotik

Sat Jun 30, 2012 11:08 pm

You can do /31 on Mikrotik.

Set interface to 10.99.99.1/32 and set broadcast to the remote end e.g. 10.99.99.2 do the opposite on the remote end.
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oreggin
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Re: /31 not useable on Mikrotik

Sat Jun 30, 2012 11:20 pm

You can do /31 on Mikrotik.

Set interface to 10.99.99.1/32 and set broadcast to the remote end e.g. 10.99.99.2 do the opposite on the remote end.
It is not clear to me. Can you please give us a config example?

Thanks,
oreggin
 
LennonNZ
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Re: /31 not useable on Mikrotik

Sun Jul 01, 2012 12:10 pm

You can do /31 on Mikrotik.

Set interface to 10.99.99.1/32 and set broadcast to the remote end e.g. 10.99.99.2 do the opposite on the remote end.
It is not clear to me. Can you please give us a config example?

Thanks,
oreggin
Umm.. that is a work around (hack) for Mikrotik -> Mikrotik as far as I know as /31 are broken.. doesn't work as far as I could tell with anything else which talks /31 properly.
 
oreggin
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Re: /31 not useable on Mikrotik

Sun Jul 01, 2012 12:43 pm

Ok, but what if I need to work with non-MT/RoS devices like cisco?
 
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docmarius
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Re: /31 not useable on Mikrotik

Sun Jul 01, 2012 2:40 pm

/31 subnetting seems in my opinion a little odd and should not work on an interface, it should work only on defining routes to get 2 IPs at once...
Rationale:
A network needs a network address, a broadcast address and an usable network host IP range...
Now subnetting using /31 gives you just 2 addresses, and since the lowest will be the network address and the highest the broadcast, there is no room for usable addresses in a /31 subnet.
Thus the smallest functional subnetting on an interface would be /30. And nothing is broken, just working as expected.

And the so called "hack" presented by nz_monkey is the solution for that particular setup, not a workaround.
Last edited by docmarius on Sun Jul 01, 2012 2:45 pm, edited 1 time in total.
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oreggin
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Re: /31 not useable on Mikrotik

Sun Jul 01, 2012 2:44 pm

Thus the smallest functional subnetting on an interface would be /30. And nothing is broken, just working as expected.
/31 doesn't brake too. Please see RFC3021.
 
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docmarius
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Re: /31 not useable on Mikrotik

Sun Jul 01, 2012 2:53 pm

@oreggin: You are right. Missed that one...

And it is logic - what is the use of a broadcast and network address in a 2 IP network :lol:

Now if MT implements it - that's another question.
Torturing CCR1009-7G-1C-1S+, RB450G, RB750GL, RB951G-2HnD, RB960PGS, RB260GSP, OmniTIK 5HnD and NetMetal 922UAGS-5HPacD + R11e-5HnD in my home network.

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