The scenario: 1 AS is shared between two datacenters. The AS has /22 prefix assigned to it, but it's divided internally to two /23s. One per each DC. DCs have one point to point fiber link and each DC has their own transit. Routers are interconnected using iBGP.

When that fiber link is up I'd like to announce both /22 and /23, but when that link breaks I'd only like to announce the more specific /23 to transit providers.

So any idea how to implement that? Basically I was thinking of having static route with BFD and if that static route goes away it would pull that covering prefix from our transit providers. So I don't blackhole the traffic for other DC when our internal fiber is down.

I'm really new to the Mikrotik platform, previously I have been using Juniper's JunOS. So I welcome all suggestions how to implement this in Mikrotik.

Basically I was thinking of having static route with BFD and if that static route goes away it would pull that covering prefix from our transit providers.

it should be /22 route, and then set 'synchronize=yes' in BGP Networks for /22

Is there a way to do this with a /32 route? So say there's 1.1.1.1/32 via iBGP then announce to eBGP peers the full /22 prefix?

Is there a way to do this with a /32 route? So say there's 1.1.1.1/32 via iBGP then announce to eBGP peers the full /22 prefix?

so, if there's 1.1.1.1/32, you want to announce 1.1.0.0/22?.. or some other prefix?

you may try to use recursive nexthop lookup...

so, if there's 1.1.1.1/32, you want to announce 1.1.0.0/22?.. or some other prefix?
you may try to use recursive nexthop lookup...

The /32 route will fall inside the /22 prefix, but it's not the nexthop.

The idea is as follows:
1.1.1.0/23 is at DC1
1.1.3.0/23 is at DC2

DC1 will announce loopback /32 in iBGP that is inside the 1.1.1.0/23 say 1.1.2.42/32.

If that route exists via iBGP at DC2 then announce to eBGP peers both 1.1.3.0/23 and 1.1.1.0/22. When that iBGP route goes away, withdraw that 1.1.1.0/22.

On Juniper side (DC1) I'm using Generated Routes to accomplish this (https://www.juniper.net/techpubs/softwa ... 59002.html)

maybe, BGP Aggregate will help? http://wiki.mikrotik.com/wiki/Manual:Ro ... #Aggregate

use summary-only=yes

maybe, BGP Aggregate will help? http://wiki.mikrotik.com/wiki/Manual:Ro ... #Aggregate
use summary-only=yes

If I'm reading that documentation correctly it will then supress the more specific advertisiment? So you can't have /22 and /23 that way. For Traffic Engineering(TE) purposes it would be good to have both advertised the same time when the link between DCs is healthy.

if you set summary-only=no then more specific routes will not be suppressed.

The issue still remains that with that aggregate it's always active as there will be more specific routes available from the DC2's half of /22.. atleast I can't see how I can specify that create 10.0.1.0/22 aggreate only when there's routes from 10.0.1.0/23 and not from 10.0.3.0/23.

Just a status update. I ended up announcing the whole /22 and /23 all the time using the bgp networks statement. Only downside is that if someone filters /23 size prefix and we happen to have the iBGP link down then some incoming traffic gets blackholed.

Thanks a lot for quick replies, really helped me to implement Mikrotik on our other DC.