I've tried with several devices now, but there's absolutely no way, I can get /31 addresses working. Is this a bug, or is it a missing feature?

For the reference:
R1 (RB450):
/ip address add interface=ether1 address=10.10.10.2/31 disabled=no
R2 (RB450)::
/ip address add interface=ether1 address=10.10.10.3/31 disabled=no

Ping times out.

No.
10.10.10.1/31 covers 10.10.10.0-10.10.10.1.
You will get a nice no route to host error with 10.10.10.1-10.10.10.2 netmask 255.255.255.254

address=10.10.10.2/31 network=10.10.10.2 broadcast=10.10.10.3 interface=ether3 actual-interface=ether3
Seems correct to me.

I would skip using an actual /31, and just use two /32s. Specify the remote address as the "network", and you should be good to go.

This mechanism is more flexible than using /31s, as the addresses don't need to be adjacent; and more efficient since you can re-use the same address for multiple links on a router.

In your particular case:

R1: /ip add add interface=ether1 address=10.10.10.2/32 network=10.10.10.3
R2: /ip add add interface=ether1 address=10.10.10.3/32 network=10.10.10.2

Will do the trick.

In a more complex hypothetical setup, with four routers connected to each other in a full-mesh of point-to-point ethernets:

R1: /ip add add interface=ether1-to-R2 address=10.10.10.1/32 network=10.10.10.2
R1: /ip add add interface=ether2-to-R3 address=10.10.10.1/32 network=10.10.10.3
R1: /ip add add interface=ether3-to-R4 address=10.10.10.1/32 network=10.10.10.4

R2: /ip add add interface=ether1-to-R1 address=10.10.10.2/32 network=10.10.10.1
R2: /ip add add interface=ether2-to-R3 address=10.10.10.2/32 network=10.10.10.3
R2: /ip add add interface=ether3-to-R4 address=10.10.10.2/32 network=10.10.10.4

R3: /ip add add interface=ether1-to-R1 address=10.10.10.3/32 network=10.10.10.1
R3: /ip add add interface=ether2-to-R2 address=10.10.10.3/32 network=10.10.10.2
R3: /ip add add interface=ether3-to-R4 address=10.10.10.3/32 network=10.10.10.4

R4: /ip add add interface=ether1-to-R1 address=10.10.10.4/32 network=10.10.10.1
R4: /ip add add interface=ether2-to-R2 address=10.10.10.4/32 network=10.10.10.2
R4: /ip add add interface=ether3-to-R3 address=10.10.10.4/32 network=10.10.10.3

Would fully interconnect them, using only 4 addresses. In this particular case, we get 3 times the address utilization efficiency of /31 addressing.

In an 8 router full-mesh the efficiency is even more spectacular, with only 8 addresses needed for /32 addressing, while a whopping 56 addresses would be needed for /31 addressing.

--Eric

Interesting concept, quite a hack!
I'm pretty sure I can't use that when the other end of the device is a cisco router, so I'm still very much wanting real /31 support. But thanks for your suggestion, it's a really cool hack

address=10.10.10.2/31 network=10.10.10.2 broadcast=10.10.10.3 interface=ether3 actual-interface=ether3
Seems correct to me.

Not I.

For MT-MT, I use /32s, and rejoice that the vast majority of my network is extremely efficient address-use wise.
For Cisco-Cisco, /31s work great, and are only slightly depressing.
For MT-Cisco, /30s seems to be the longest common netmask that works properly with OSPF, so I go with it, and mourn the lost utility.

--Eric

I would skip using an actual /31, and just use two /32s. Specify the remote address as the "network", and you should be good to go.

This mechanism is more flexible than using /31s, as the addresses don't need to be adjacent; and more efficient since you can re-use the same address for multiple links on a router.

In your particular case:

R1: /ip add add interface=ether1 address=10.10.10.2/32 network=10.10.10.3
R2: /ip add add interface=ether1 address=10.10.10.3/32 network=10.10.10.2

Will do the trick.

In a more complex hypothetical setup, with four routers connected to each other in a full-mesh of point-to-point ethernets:

R1: /ip add add interface=ether1-to-R2 address=10.10.10.1/32 network=10.10.10.2
R1: /ip add add interface=ether2-to-R3 address=10.10.10.1/32 network=10.10.10.3
R1: /ip add add interface=ether3-to-R4 address=10.10.10.1/32 network=10.10.10.4

R2: /ip add add interface=ether1-to-R1 address=10.10.10.2/32 network=10.10.10.1
R2: /ip add add interface=ether2-to-R3 address=10.10.10.2/32 network=10.10.10.3
R2: /ip add add interface=ether3-to-R4 address=10.10.10.2/32 network=10.10.10.4

R3: /ip add add interface=ether1-to-R1 address=10.10.10.3/32 network=10.10.10.1
R3: /ip add add interface=ether2-to-R2 address=10.10.10.3/32 network=10.10.10.2
R3: /ip add add interface=ether3-to-R4 address=10.10.10.3/32 network=10.10.10.4

R4: /ip add add interface=ether1-to-R1 address=10.10.10.4/32 network=10.10.10.1
R4: /ip add add interface=ether2-to-R2 address=10.10.10.4/32 network=10.10.10.2
R4: /ip add add interface=ether3-to-R3 address=10.10.10.4/32 network=10.10.10.3

Would fully interconnect them, using only 4 addresses. In this particular case, we get 3 times the address utilization efficiency of /31 addressing.

In an 8 router full-mesh the efficiency is even more spectacular, with only 8 addresses needed for /32 addressing, while a whopping 56 addresses would be needed for /31 addressing.

--Eric

Is this usable in production networks?
Where's the catch?

BR,
M

Using it in my production network without problems.
Of course, Only Mikrotik supports this. That's the only limitation

Is this usable in production networks?
Where's the catch?

BR,
M

Using it in my production network without problems.
Of course, Only Mikrotik supports this. That's the only limitation

Is this usable in production networks?
Where's the catch?

BR,
M

Does this tweak work with OSPF?

What kind of problems you have with TE?

If the subnet is /31 would you not need to use:

10.10.10.1/31 and 10.10.10.2/31

I have run into this because only two addresses are allowed it will expect the equal amount of Ips in the subnet 10.10.10.3/31 would belong with 10.10.10.4/31

Using it in my production network without problems.
Of course, Only Mikrotik supports this. That's the only limitation

Is this usable in production networks?
Where's the catch?

BR,
M

Using it in my production network without problems.
Of course, Only Mikrotik supports this. That's the only limitation

Is this usable in production networks?
Where's the catch?

BR,
M

Routing a /32 via another /32 has been used for years in Telco DSL networks on a multitude of vendor equipment like Cisco, Adtran, etc...

It's a very popular network design when using a PPPoE BRAS

The technique that is being referred to in earlier posts really uses routing via interface rather than via a specific gateway IP. The method described causes RouterOS to place connected routes in the routing table for the remote IPs but a very similar arrangement with static routes can be achieved as follows:

Make an ARP capable layer 2 network available between 2 RouterOS devices - it can be an Ethernet, VLAN or whatever you can arrange.
Place a /32 IP number "IP A" on Router A.
Place a /32 IP number "IP B" on Router B.
Now add a route on Router A with IP B as the destination and the interface connecting Router A to Router B as the gateway.
Now add a route on Router B with IP A as the destination and the interface connecting Router B to Router A as the gateway.

Router A should now be able to ping Router B on IP B and vice versa should also work. IP A and IP B do not need to be IP numbers remotely close together. This approach works on plenty of routing engines from many suppliers.

It simply forces the routing engine to ARP for the destination IP on the relevant interface.

/ip address add address=172.16.0.1/32 network=172.16.0.1 interface=eoip-tunnel1
/ip address add address=10.0.0.1/24 network=10.0.0.0 interface=bridge-local
/ip route add dst-address=172.16.0.2/32 gateway=eoip-tunnel1
/ip route add dst-address=10.0.1.0/24 gateway=172.16.0.2

/ip address add address=172.16.0.2/32 network=172.16.0.2 interface=eoip-tunnel1
/ip address add address=10.0.1.1/24 network=10.0.1.0 interface=bridge-local
/ip route add dst-address=172.16.0.1/32 gateway=eoip-tunnel1
/ip route add dst-address=10.0.0.0/24 gateway=172.16.0.1

I think you are hitting a restriction on next hops not being resolvable via interface routes. I'm not sure what your overall aim is so not sure of best solution, however as a technical point note that if you make both the 10.x.x.x routes interface routes - i.e. set the EoIP tunnel interface as the gateway - and enable proxy-arp at both ends of the EoIP tunnel then you should be able to ping the 10.x.x.x addresses fine in both direction.

I'm not sure of the overall picture. Are these /32s public IPs you are assigning or /32s provided by an ISP at each location?

If they are RFC1918 addresses why do you want to do anything other than use a /30? Conservation of non-RFC1918 addresses is what drives people into /31 & /32 land usually.....

If you add proxy-arp and use the eoip interface as the gateway(s) above then you will be able to ping those 10.x.x.x blocks both ways. However, whether that would be acceptable in a real world scenario might depend on a few other factors.

If they are RFC1918 addresses why do you want to do anything other than use a /30? Conservation of non-RFC1918 addresses is what drives people into /31 & /32 land usually.....

using the /32 on the MT solves it perfectly!

I would skip using an actual /31, and just use two /32s. Specify the remote address as the "network", and you should be good to go.

This mechanism is more flexible than using /31s, as the addresses don't need to be adjacent; and more efficient since you can re-use the same address for multiple links on a router.

In your particular case:

R1: /ip add add interface=ether1 address=10.10.10.2/32 network=10.10.10.3
R2: /ip add add interface=ether1 address=10.10.10.3/32 network=10.10.10.2

Will do the trick.

In a more complex hypothetical setup, with four routers connected to each other in a full-mesh of point-to-point ethernets:

R1: /ip add add interface=ether1-to-R2 address=10.10.10.1/32 network=10.10.10.2
R1: /ip add add interface=ether2-to-R3 address=10.10.10.1/32 network=10.10.10.3
R1: /ip add add interface=ether3-to-R4 address=10.10.10.1/32 network=10.10.10.4

R2: /ip add add interface=ether1-to-R1 address=10.10.10.2/32 network=10.10.10.1
R2: /ip add add interface=ether2-to-R3 address=10.10.10.2/32 network=10.10.10.3
R2: /ip add add interface=ether3-to-R4 address=10.10.10.2/32 network=10.10.10.4

R3: /ip add add interface=ether1-to-R1 address=10.10.10.3/32 network=10.10.10.1
R3: /ip add add interface=ether2-to-R2 address=10.10.10.3/32 network=10.10.10.2
R3: /ip add add interface=ether3-to-R4 address=10.10.10.3/32 network=10.10.10.4

R4: /ip add add interface=ether1-to-R1 address=10.10.10.4/32 network=10.10.10.1
R4: /ip add add interface=ether2-to-R2 address=10.10.10.4/32 network=10.10.10.2
R4: /ip add add interface=ether3-to-R3 address=10.10.10.4/32 network=10.10.10.3

Would fully interconnect them, using only 4 addresses. In this particular case, we get 3 times the address utilization efficiency of /31 addressing.

In an 8 router full-mesh the efficiency is even more spectacular, with only 8 addresses needed for /32 addressing, while a whopping 56 addresses would be needed for /31 addressing.

--Eric

As MT doesn't work well with /31's the only way to interconnect MT<->OtherVendor is by /30's

Linux support /32 so switch to /32

and OSPF will work.

change to
network 172.16.64.58/32 area 0.0.0.112

Is there any fundamental reason why mikrotik does not support RFC 3021, so it is compatible with other vendors (cisco) without problems?

I would skip using an actual /31, and just use two /32s. Specify the remote address as the "network", and you should be good to go.

This mechanism is more flexible than using /31s, as the addresses don't need to be adjacent; and more efficient since you can re-use the same address for multiple links on a router.

In your particular case:

R1: /ip add add interface=ether1 address=10.10.10.2/32 network=10.10.10.3
R2: /ip add add interface=ether1 address=10.10.10.3/32 network=10.10.10.2

Will do the trick.

In a more complex hypothetical setup, with four routers connected to each other in a full-mesh of point-to-point ethernets:

R1: /ip add add interface=ether1-to-R2 address=10.10.10.1/32 network=10.10.10.2
R1: /ip add add interface=ether2-to-R3 address=10.10.10.1/32 network=10.10.10.3
R1: /ip add add interface=ether3-to-R4 address=10.10.10.1/32 network=10.10.10.4

R2: /ip add add interface=ether1-to-R1 address=10.10.10.2/32 network=10.10.10.1
R2: /ip add add interface=ether2-to-R3 address=10.10.10.2/32 network=10.10.10.3
R2: /ip add add interface=ether3-to-R4 address=10.10.10.2/32 network=10.10.10.4

R3: /ip add add interface=ether1-to-R1 address=10.10.10.3/32 network=10.10.10.1
R3: /ip add add interface=ether2-to-R2 address=10.10.10.3/32 network=10.10.10.2
R3: /ip add add interface=ether3-to-R4 address=10.10.10.3/32 network=10.10.10.4

R4: /ip add add interface=ether1-to-R1 address=10.10.10.4/32 network=10.10.10.1
R4: /ip add add interface=ether2-to-R2 address=10.10.10.4/32 network=10.10.10.2
R4: /ip add add interface=ether3-to-R3 address=10.10.10.4/32 network=10.10.10.3

Would fully interconnect them, using only 4 addresses. In this particular case, we get 3 times the address utilization efficiency of /31 addressing.

In an 8 router full-mesh the efficiency is even more spectacular, with only 8 addresses needed for /32 addressing, while a whopping 56 addresses would be needed for /31 addressing.

--Eric

@TomjNorthidaho, some creative thinking there, I might pop your balloon though
That method is called point to point addressing and but should work

/31 network between two mikrotik devices - here is how you do it

First thing - you do not actually use a /31 in the IP address ( this is important )

Here is how you use a /31 network of only two IP address to get two Mikrotik devices to talk to each other.

I am going to demonstrate 192.168.168.0/31 ( This /31 has only two IP address which are 192.168.168.0 and 192.168.168.1 )
Mikrotik #1
- Configure IP address 192.168.168.0 on your first Mikrotik ( example 192.168.168.0 ( no / after IP address ) will be on ether2 )
- Add the route 192.168.168.1 out interface ether2 ( use the interface name not an IP address )

Mikrotik #2
- Configure IP address 192.168.168.1 on your second Mikrotik ( example 192.168.168.1 ( no / after IP address ) will be on ether2 )
- Add the route 192.168.168.0 out interface ether2 ( use the interface name not an IP address )

Thats it , the two mikrotiks can ping each other and pass traffic

So , why burn up 4 IPv4 address on a link with only two Mikrotiks on the link. Each /30 link between two Mikrotik devices can now be used for two different /31 links ( twice as many link using the same number of IP address ).

North Idaho Tom Jones

/31 network between two mikrotik devices - here is how you do it

First thing - you do not actually use a /31 in the IP address ( this is important )

Here is how you use a /31 network of only two IP address to get two Mikrotik devices to talk to each other.

I am going to demonstrate 192.168.168.0/31 ( This /31 has only two IP address which are 192.168.168.0 and 192.168.168.1 )
Mikrotik #1
- Configure IP address 192.168.168.0 on your first Mikrotik ( example 192.168.168.0 ( no / after IP address ) will be on ether2 )
- Add the route 192.168.168.1 out interface ether2 ( use the interface name not an IP address )

Mikrotik #2
- Configure IP address 192.168.168.1 on your second Mikrotik ( example 192.168.168.1 ( no / after IP address ) will be on ether2 )
- Add the route 192.168.168.0 out interface ether2 ( use the interface name not an IP address )

Thats it , the two mikrotiks can ping each other and pass traffic

So , why burn up 4 IPv4 address on a link with only two Mikrotiks on the link. Each /30 link between two Mikrotik devices can now be used for two different /31 links ( twice as many link using the same number of IP address ).

North Idaho Tom Jones

The main issue that i've run into with this method is routing protocol instability. I've had intermittent issues with OSPF adjacency instability on a number of networks that used this addressing method. As soon as we migrated to /30 or larger prefix, the issues went away.

So I am on the verge of setting up a BGP with my 1st peer and he mentioned using a /31. I am going to assume he is using a Cisco. I am a Mikrotik shop.

You are saying that Cisco and Mikrotik are not able to use BGP on a /31?

Rick

turnip, this should resolve all issues: viewtopic.php?f=14&t=32935#p772755

Normis, it seems /31 works fine on RouterOS v6 stable/long-term though?

but they fail when you use protocols that expect to be able to use broadcast over a link, like OSPF.

turnip, this should resolve all issues: viewtopic.php?f=14&t=32935#p772755

but they fail when you use protocols that expect to be able to use broadcast over a link, like OSPF.

This partially untrue, as OSPF has PtP mode which eliminates address broadcasts, making /32 addresses the absolute simplest and easiest option, but only for PtP mode OSPF.

I'm relying on OSPF as IGP, as well as BGP and MPLS, so I'm not going to do this...
Would be nice if MikroTik fixed this. It shouldn't be that hard.