ECMP with OSPF trouble

RouterOS Forwarding Protocols
1

Good morning.

I have a question with ECMP: i would like to know if it’s possible or what alternatives there are to do load balancing in this tophology with OSPF or another IGP:

 R1 --------> Sw1 --------> |
               |            | R2
               |__________> | 
               
R1  = CCR2004 (router with OSPF)
Sw1 = CRS317 (switch)
R2  = RB4011 (router with OSPF)

R1 → Sw1 is a 10Gbps FO link
Sw1 ->R1 they are 2 wireless links

R1 SIDE:
/routing ospf instance print
Flags: X - disabled, I - inactive 
 0   name="default-v2" version=2 vrf=main router-id=172.24.1.1 originate-default=never 
 
/routing ospf interface-template
add area=backbone-v2 comment="R1->R2 1st link" cost=10 interfaces=bridge1 networks=172.23.0.12/30 priority=1 type=ptp
add area=backbone-v2 comment="R1->R2 2nd link" cost=10 interfaces=bridge1 networks=172.23.0.36/30 type=ptp

/routing ospf neighbor print
1  D instance=default-v2 area=backbone-v2 address=172.23.0.14 router-id=192.168.251.21 state="Full" state-changes=10 adjacency=1d11h9m17s timeout=32s 
8  D instance=default-v2 area=backbone-v2 address=172.23.0.38 router-id=192.168.251.21 state="Full" state-changes=6 adjacency=5m29s timeout=31s

/routing route print where dst-address="192.168.251.0/27"
Flags: A - ACTIVE; o, y - COPY; +, B - BLACKHOLE
Columns: DST-ADDRESS, GATEWAY, AFI, DISTANCE, SCOPE, TARGET-SCOPE, IMMEDIATE-GW
    DST-ADDRESS       GATEWAY              AFI  DISTANCE  SCOPE  TARGET-SCOPE  IMMEDIATE-GW       
Ao+ 192.168.251.0/27  172.23.0.14%bridge1  ip4       110     20            10  172.23.0.14%bridge1
Ao+ 192.168.251.0/27  172.23.0.38%bridge1  ip4       110     20            10  172.23.0.38%bridge1

/ip route print det where dst-address=192.168.251.0/27
Flags: D - dynamic; X - disabled, I - inactive, A - active; c - connect, s - static, r - rip, b - bgp, o - ospf, d - dhcp, v - vpn, m - modem, y - copy; H - hw-offloaded; + - ecmp 
   DAo + dst-address=192.168.251.0/27 routing-table=main gateway=172.23.0.14%bridge1 immediate-gw=172.23.0.14%bridge1 distance=110 scope=20 target-scope=10 suppress-hw-offload=no 

   DAo + dst-address=192.168.251.0/27 routing-table=main gateway=172.23.0.38%bridge1 immediate-gw=172.23.0.38%bridge1 distance=110 scope=20 target-scope=10 suppress-hw-offload=no

But traffic is using only the first route via 172.23.0.14 and ignoring the second one.

Any help would be appeciated!

2

OSPF will not load balance the way that you are thinking and with only two connections it will duplex the link typically, you can use ECMP but that is a bit harder to setup. If you don’t need OSPF you can use mangle rules and routing marks and per connection classifiers to accomplish the same thing.

https://wiki.mikrotik.com/wiki/Manual:IP/Route#Multipath_.28ECMP.29_routes

3

Thank you for your tip.

I did something similar: i created a route table with a default route pointing to the empty link with check_gateway=arp. Then I created some route rules to force some destinations to the empty link.

I’m not so happy but it’s working

/routing table add fib name=via-af5-2
/ip route add check-gateway=arp disabled=no distance=1 dst-address=0.0.0.0/0 gateway=172.23.0.38 pref-src=0.0.0.0 routing-table=via-af5-2 scope=30 suppress-hw-offload=no target-scope=10
/routing rule add action=lookup disabled=no dst-address=192.168.249.0/24 table=via-af5-2
4

This post is a little stale but hopefully you noticed the later thread: http://forum.mikrotik.com/t/ospf-load-balancing-broken-in-v7-1-1/155109/1

What you’re describing is technically doable and according to your output, the two OSPF routes are installed with a + for ECMP. It seems like you probably hit the bug with ECMP on CCR2004 rather than anything actually being wrong.