Point-to-point (/31) addresses

StubArea51 · Wed Feb 04, 2015 7:22 pm

I could go either way on that...it would be nice to have, but given all the development features requested of MikroTik , I'd rather see MPLS fast reroute or BGP ECMP before /31 addresses.

nicktc · Mon Jul 25, 2016 1:09 am

Sorry if I'm reviving a really old thread, however..

Using 10.0.0.A/32 to link router A-B-C together things that work great:
- OSPF
- MPLS
- LDP
- VPLS (point to point between A-B or B-C)

Things that do not work correctly
- VPLS (between A-C no data RX on either router)

Adding an additional loopback address and using it as a transport address seems to "fix" the problem.

This is on 6.36

Anyone else seeing the same issue?

asy · Tue Feb 27, 2018 1:20 pm

Are there any plans to support RFC 3021 in RouterOS now ?

JimmyNyholm · Tue Feb 27, 2018 5:46 pm

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

This is the way I have tried this with routing protocols ospf and bgp and mpls it all works so my definite recommendation MT<->MT scenario is /32 and use the same IP for all local interfaces on one router. this eliminates the need for loopback interface as the router is the same IP to all interfaces. As MT doesn't work well with /31's the only way to interconnect MT<->OtherVendor is by /30's

asy · Tue Feb 27, 2018 8:36 pm

I read about MT-MT with /32.

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

But I need this. I linked MT(/32) - Linux(/31) but I can't run OSPF over it (with Quagga). I tried nbma, broadcast
and point-to-point settings for OSPF but all unsuccessful. The best that I reach (with nbma, from log of Quagga):

OSPF: Packet 172.16.64.58 [Hello:RECV]: NetworkMask mismatch on eth2:172.16.64.59 (configured pref
ix length is 31, but hello packet indicates 32).

eth2/Linux: 172.16.64.59/31

RouterOS:
/ip address
add address=172.16.64.58 interface=ether1 network=172.16.64.59

So, does no way to run OSPF without /30 ?

Wed Feb 28, 2018 11:36 am

Linux support /32 so switch to /32 and OSPF will work.

asy · Wed Feb 28, 2018 3:33 pm

Linux support /32 so switch to /32

True. I switched "ip address add 172.16.64.59/31 ..." to "ip address add 172.16.64.59/31 peer 172.16.64.59 ..." and link continued to work. Ok.

and OSPF will work.

But this not. Quagga isn't up neighbor with error (with nbma):

OSPF: interface eth2:172.16.64.59: ospf_read network address is not same [172.16
.64.58]

I attempted to switch ospf configuration to point-to-point. This gave some result: I can see neighbor in Quagga now:

172.16.64.58 1 Init/DROther 37.334s 172.16.64.58 eth2:172.16.64.59 0 0 0

but I doesn'ot see neighbor in RouterOS.

Wed Feb 28, 2018 3:38 pm

show your quagga configuration

asy · Wed Feb 28, 2018 4:48 pm

Sorry, I forgot about default firewall after reset configuration on MT. It works, thanks.

Linux:

ip address add 172.16.64.59/32 peer 172.16.64.58 dev eth2

Quagga:

!
  interface eth2
  ip ospf network point-to-point
! 
 router ospf
  ospf router-id 10.10.10.10
!
  network 172.16.64.58/31 area 0.0.0.112
!
  area 0.0.0.112 stub
!

MT (6.41.2)

/ip address
add address=172.16.64.58 interface=ether1 network=172.16.64.59
/routing ospf area
set [ find default=yes ] disabled=yes
add area-id=0.0.0.112 default-cost=1 inject-summary-lsas=yes name=stub-area1 type=stub
/routing ospf interface
add interface=ether1 network-type=point-to-point
/routing ospf network
add area=stub-area1 network=172.16.64.58/31

Wed Feb 28, 2018 5:16 pm

change to
network 172.16.64.58/32 area 0.0.0.112

asy · Thu Mar 01, 2018 9:08 am

change to
network 172.16.64.58/32 area 0.0.0.112

It seems more accurate but it not works: Quagga is not sending OSPF hello.

indnti · Fri Jul 20, 2018 2:48 am

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

schadom · Sat Sep 29, 2018 3:07 pm

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

Same as with many other things here...
Hundreds of requests by many customers over years and they simple ignore it

dcosta · Tue Nov 27, 2018 1:33 pm

Hello,
Now that Mikrotik addressed the service providers segment with CCR routers, when does Mikrotik plan to support /31 networks?
The majority of routers used by service providers supports /31, so it will be hard to migrate from a previous /31 configuration to Mikrotik CCR routers.
Thanks,
David

indnti · Fri Sep 20, 2019 12:39 pm

Hi

Any News for this?

chillisock7 · Fri Jan 31, 2020 9:28 pm

Brilliant

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

StubArea51 · Sat Feb 01, 2020 5:52 pm

Just a warning on using two /32 addresses as a workaround for the /31 problem.

We've had a number of problems with OSPF stability using this approach if you're planning on using OSPF for a dynamic routing protocol.

jw1 · Wed May 06, 2020 12:54 am

Working on switching up some /30 to /32 in order to free up some addresses. So far haven't noticed stability issues, but path selection seems a bit odd.
Here's the rundown:
R1 is connected to R2. R1 interface to R2 has a /32 address, for example, 1.1.1.1/32 with network 2.2.2.2. R2 facing R1 is 2.2.2.2/32 with network 1.1.1.1. Connectivity seems OK, but in the routing table on R1, 2.2.2.2 shows up as directly connected, distance 0, but 1.1.1.1 doesn't show up at all. No big deal, just a little odd.
Add R3 and R4. R1 -> R2 -> R3 -> R4 -> back to R1 and add OSPF. Now on the R1 routing table 1.1.1.1 shows up, but as an OSPF route with a distance of 110. Looking in OSPF routes, 1.1.1.1 has a path cost of 20 with a gateway of 2.2.2.2. Odd that a local address would have a path cost of 20, but things still seem to be working, so OK.
Here's the potential gotcha - On R4 routing table the path to 1.1.1.1 has equal preference between going directly from R4-R1 and R4-R3-R2-R1. In the OSPF routes, both options have a path cost of 30 even though 1 path is 1 hop away and the other is 3. All the individual path costs are 10. A traceroute from R4 to 1.1.1.1 chooses the R4-R3-R2-R1 path. To be honest, I doubt I will be needing to connect to the IP address of a PTP link, and the path selection for the loopback address of R1 seems normal, but it is making me wonder if I want to proceed with more switching to /32s. I am thinking about tinkering with a static route on R1 to 1.1.1.1 to see what happens.

(FWIW, these aren't the actual IPs I was using and haven't tested it with these. Also, I doubt if it matters, but the lowest router id for path selection is R3, R4, R2, and then R1)

jw

chakphanu · Fri Jun 26, 2020 5:26 pm

Cisco /31 - MT/31 BFD not work
Cisco /31 - MT/32 BFD Work

next111 · Fri Jul 03, 2020 10:23 pm

serves the / 31 here in Italy is widely used on wan

Sat Aug 01, 2020 2:04 am

/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

CZFan · Mon Aug 03, 2020 1:02 am

@TomjNorthidaho, some creative thinking there, I might pop your balloon though

That method is called point to point addressing and but should work

Mon Aug 03, 2020 5:26 pm

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

One thing I have not tested is a /31 between a Mikrotik and a Cisco , or between a Mikrotik and a PfSense virtual router/firewall.

North Idaho Tom Jones

StubArea51 · Tue Aug 04, 2020 6:52 pm

/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.

Wed Aug 05, 2020 12:26 am

/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.

I wish that Mikrotik would support a /31 natively on a /31 network between any two Mikrotiks.
With IPv4 exhausted and no more new IPv4 blocks available, it is becoming increasingly important-urgent-required to natively support /31 networks , without the need to do any fancy work-arounds.
I've run into several problems with peer-connections where a remote party is wanting to use a /31 ( a /31 network for BGP peering ). I gave up trying to make it work and had to fight to use a /30 for BGP peering - what a friggen nightmare that was !

North Idaho Tom Jones

sjwrick · Fri Aug 07, 2020 5:23 pm

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

Fri Aug 07, 2020 6:27 pm

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

When I was adding a second BGP peer, I was given one IP address from a /31. I had a Mikrotik ( I don't know what the upstream BGP router was ). I tried and tried and tried using a /31 and at the time I could not get it to even ping his /31 IP address. This was my first attempt at trying to use a /31.
As a test, I switched to a Cisco router and the /31 worked , but I wanted to use a Mikrotik router for my BGP. I was finally able to get the BGP peering network changed from a /31 to a /30 and suddenly everything started working on my Mikrotik router.

Sooo , although it might be possible to make a Mikrotik function on a /31 network for BGP peering, I suggest using a traditional /30 network for BGP peering. A /30 network for BGP peering will give you the ability to change your Mikrotik BGP peering router to any other BGP peering router. If you setup a /31 network for BGP peering , then you might get stuck to only being able to use routers which natively support /31 networks for BGP peering.

So , IMO - for BGP peering , I suggest using existing traditional tried-and-true /30.

North Idaho Tom Jones

pe1chl · Fri Aug 07, 2020 7:59 pm

Of course when you have only a simple peering with some other world where they are using /31, you can just change your own side to be a /30 or even larger to
make your side contain the addresses from the /31 and neither of them being the "network" or "broadcast" address on that subnet.
This will make some addresses unreachable, but when the /31 is from a range that is just used for such peerings, that usually does not matter.

When you want to setup your local shop using /31 and have a mix of routers that allow that and MikroTiks that don't, this could be more of a problem because there
is more risk fo connectivity issues in that case.

turnip · Wed Jul 14, 2021 9:52 am

Any movement on this? Every IP Transit provider I've looked at provides a /31.

Wed Jul 14, 2021 10:04 am

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

DarkNate · Wed Jul 14, 2021 11:18 am

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? I've seen many ASNs doing it just fine?

Cablenut9 · Wed Jul 14, 2021 4:12 pm

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

/32 really cuts down on addresses though, and it follows the philosophy of "hosts have IP addresses, not interfaces"

pe1chl · Wed Jul 14, 2021 4:44 pm

Tricks with /32 (or even /31) work OK for point-to-point traffic like static routing or BGP peers, but they fail when you use protocols that expect to be able to use broadcast over a link, like OSPF. You may need additional configuration, you may encounter bugs, etc.
As long as you know that, it should be fine.

Cablenut9 · Wed Jul 14, 2021 11:45 pm

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.

turnip · Thu Jul 15, 2021 8:46 am

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

Thanks Normis
I'd tried this in a lab and it worked fine with static routing, but the network manager at my ISP reported that they couldn't get it to work with BGP. I haven't tested it myself as I don't have an ASN yet.
They use Cisco routers and have a client with a Mikrotik CCR.
These guys are flexible enough to offer a /30 or whatever we need, but other providers mightn't be.

pe1chl · Thu Jul 15, 2021 11:02 am

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.

That is what I say, you may need additional configuration. And I have also seen people reporting problems with that.
But I have no personal experience with it, I do not use /31 or /32 in the network.

itmethod · Fri Jul 22, 2022 8:40 pm

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.

Set OSPF to PTP instead of broadcasting on the Mikrotik. for this interface.

Point-to-point (/31) addresses

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

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