ROS V7 BGP Advertisement Question

RouterOS Forwarding Protocols
1

I am working on converting a v6 BGP setup to a new router running V7 and have a question on the advertisements.

Here is the example setup (Using private IPs just for example purposes)

BGP Peer1 (172.16.5.1)->border router eth1 → border router eth3 → core router eth1
BGP Peer2 (172.16.10.1)->border router eth2 → border router eth3 ->core router eth1

Border router
eth1 - 172.16.5.2/30
eth2 - 172.16.10.2/30
eth3 - 172.16.2.1/30
Core router
eth1 - 172.16.2.2/30
eth2 - 192.168.97.1/24
eth3 - 192.168.104.1/24

In v6 I know I put my networks to advertise in the BGP->Networks section. So for an example I have the following. I have changed the IPs so as to not show my public IP ranges.

BGP Network (synchronize set to no)
192.168.96.0/20
192.168.96.0/21
192.168.104.0/21

Routing filter
Out-peer-1 (prefix 192.168.96.0/20; accept)
Out-peer-1 (prefix 192.168.96.0/21; accept)
Out-peer-2 (prefix 192.168.96.0/20; accept)
Out-peer-2 (prefix 192.168.104.0/21; accept)

I have this setup this was as I have two BGP connections with my upstream provider and I manually load balance by advertising my full range out both and then my upper range /21 out one and the lower range /21 out the other using the outbound routing filters . This way incoming traffic will prefer the /21 but if one feed goes down then the other traffic will then use the /20 to find my network.

In my border router routing table I have just the one route towards my core of 192.168.96.0/20 with a gateway of 172.16.2.2. I do not have any routes blackholed. This functions properly with no issue in v6.

In v7 I know to put the advertised networks as an Address list and I have my outbound filtering rules converted as well. My confusion is around the example here (https://help.mikrotik.com/docs/display/ROS/ROSv7+Basic+Routing+Examples) where it states that now in v7 routes will not be advertised unless they exist in the routing table. Also they show blackholing their route

So in v7 do I have to put all three advertised routes in the routing table or will just having the single 192.168.96.0/20 route suffice and still allow for the advertisements of both the /21s to be received by the my peers? Also do I have to have the blackhole for my prefixes?

2

Currently, you need exact match, so if you are trying to advertise /21 routes then there must be corresponding routes in the routing table. You cannot add one generic /20 route, to advertise /21 routes.

3

Got it so in my v7 routing table I would have to have

192.168.96.0/20
192.168.96.0/21
192.168.104.0/21

Do all three routes have to be enabled? Could I put in the /21s and set them ‘disabled’?
Also the distance value for each route does not matter for the BGP advertisement, so I could have the /21s at say distance=244 and the /20 at distance=1? Just as long as all three specific routes are in the table.

4

Routes need to be active, disabled routes won’t cut.

5

so let say we have multiple /30 from 192.168.96.0/20 address space and not all of them allocated yet to customers, how should we advertise 192.168.96.0/20 ?
just put it into loopback on ebgp router ?
afaik, we are not allowed advertise smaller than /24.

6

add /20 blackhole route

7

about the /20 blackhole route I have this scenario.

Router 1 advertises
100.115.102.0/24
100.115.103.0.24
100.115.96.0/20 *Summarized route for redundancy propose.

Receives
0.0.0.0/0 via BGP

Router 2 advertises
100.115.105.0/24
100.115.107.0/24
100.115.96.0/20 *Summarized route for redundancy propose.

Receives
0.0.0.0/0 via BGP

I have a connection metro E between Router 1 & Router 2.

Let say Router 1 goes down, Router 2 then try to reach router 1 routes via the blackhole route, since is the longest match to the destinations 100.115.102/24 & 10.115.103.0/24

How can I avoid this?

Router OS v6 Is not a problem since I don’t have to set the blackhole route, this issue is with Router OS v7.

Thanks

8

maybe this can help

https://help.mikrotik.com/docs/display/ROS/Moving+from+ROSv6+to+v7+with+examples
networks.png