I’m running OSPF in a mixed environment: two RB1100AH boxes (ROS 5.25) as PPPoE servers, VRRP and DHCP; two Vyatta boxes (VC 6.6) as BGP routers.
It would be nice to be able to use /31 subnets for point-to-point links between the routers, saving the precious public IP addresses.
However, it doesn’t work for me with ROS 5.25 (not brave enough to try 6.0 just yet), any plans to make it work?
The routers can ping each other just fine using the /31 addresses, but no OSPF adjacency is formed.
It works between MT boxes with /32 (re-using loopback IP addresses, specifying the other end as network) instead - nice trick.
But, this doesn’t work with Vyatta (can specify a /32 interface address, but no network address) - on the other hand, /31 works between Vyatta boxes.
Between MT and Vyatta, I have to waste IP addresses using the old fashioned /30 (or a common /29 subnet for up to 6 routers).
The issue is with OSPF only, BGP peering works fine over a /31 between my Vyatta and peer’s MT (RB1100AHx2 running ROS 5.15).
/31 is not supported.. You should use /32 or /30
Do you mean /31 is “not supported” in general, or just for OSPF? If would be bad if it works with peer’s ROS 5.15 by accident, and breaks when they upgrade.
Please consider supporting it, as described in RFC3021. No problem to use /32 between MT boxes but not everyone supports it, and /30 is a waste.
+1
Not supported in general.
Cannot understand why RouterOS supports /32 and /30 but not /31
I’'m asking both MikroTik to support /31 (in ROS v6, understand it may be too late to add in v5) and Vyatta to support /32. Currently using Vyatta for BGP, but if MikroTik gets there first, I promise to buy a new CCR or two 
Support for /31 p2p link on ethernet ports would be super, I have several p2p links and I am wasting an huge amount of IP addresses allocating a /30 fore each.
Digging through the forum I found the way to use only 2 IP addresses for Ethernet P2P links running with OSPF (examples between brackets):
- Set the interface with a /32 ip address. (10.0.0.2/32) and the network address with the remote endpoint IP address (10.0.0.3).
- Set the /ip ospf network accordingly (10.0.0.2/31).
- ???
- Profit.
As I said in the first post, I know about it. Actually the addresses don’t have to be contiguous, can be re-used from other interfaces, and it’s enough to specify the remote /32 as the OSPF network (10.0.0.3/32). This is very good, except it’s not universally supported - works between MikroTik routers and not much else.
On the other hand, /31 is still better than /30 and is well supported by other vendors, so it would be nice if MikroTik could support it too (at least in v6).
Instead of using /31, try to add /32 on the interface and add a host route
/ip address add address=1.2.3.4/32 interface=ether1
/ip route add dst-address=1.2.3.5/32 gateway=ether1