Community discussions

MikroTik App
 
millenium7
Long time Member
Long time Member
Topic Author
Posts: 538
Joined: Wed Mar 16, 2016 6:12 am

Customer and ISP failover not working as expected

Mon Aug 30, 2021 12:19 pm

Image

This basic diagram illustrates whats going on. We provide internet for a customer that has 2 sites, those sites are linked and by default both will use the much faster and more reliable primary link. This works perfectly fine
Customer routers have OSPF between them to share routes (distribute default route when available)
ISP Routers run OSPF internally, but run BGP between penultimate routers and public facing routers (there's a valid reason for not running OSPF entirely internally)
So there is route redistribution happening between internal ISP routers, and public internet ingress/egress points. Unsure if this matters, more on that below
C2 router has a static default route pointing to R3 with a distance of 250, and vice versa
Customer connects via PPPoE through the primary, all is well, everything is reachable as intended
Link between C1 and R1 goes down, everything fails over to the backup and all is still reachable, as intended

Here's the problem, when restoring the link between C1 and R1, traffic does not flow properly
R3 refuses to learn about additional routes, it does not install the BGP routes for C1/C2 in the routing table at all, it only contains the static routes with distance of 250

The reason I say above that I don't believe redistribution is a factor here, is because C1 does install the correct default route (pointing to R1). However C2 refuses to learn it from C1 and insists on again only having the backup default route in its routing table
When I manually disable the backup route in C2, it will then learn a default route via OSPF from C1

At this point both still have asymmetrical routing (traffic going out primary path, but coming in via backup path)
Again I must manually disable the backup routes in R3 for it to learn BGP routes through primary transit

They aren't in the routing table in a less preferred state, they just do not get installed in the routing table at all

Any help here? I'm not sure if this is intended behavior to prevent loops and thus routes aren't even being learned, but it's an entirely valid scenario that needs a valid solution
 
millenium7
Long time Member
Long time Member
Topic Author
Posts: 538
Joined: Wed Mar 16, 2016 6:12 am

Re: Customer and ISP failover not working as expected

Tue Aug 31, 2021 5:44 am

I've just labbed this and it still happens
In essence it's a problem with OSPF. If the source of the route is redistributed (i.e. an external route) then it will not install in the routing table if a route already exists

I've tested this with Static, BGP and other OSPF instance routes. If redistributed into the ISP OSPF network, then it will not install it in the main routing table until the existing routes are removed

This is a problem.......... how do I overcome this?
 
millenium7
Long time Member
Long time Member
Topic Author
Posts: 538
Joined: Wed Mar 16, 2016 6:12 am

Re: Customer and ISP failover not working as expected

Thu Sep 02, 2021 3:07 am

Seemingly the same problem was reported 4 years ago
viewtopic.php?t=119493

MikroTik please implement a feature (even if just in CLI) to override this behavior.
It's not like this is a super niche scenario. Having a static route as a backup with OSPF internally is exceedingly common

At the moment my only sort-of-kind-of solution is extremely convoluted (with IPIP tunnel and using BGP between ISP and customer, as well as internally on customer routers, and not using OSPF at all to distribute a default route........)

Who is online

Users browsing this forum: No registered users and 21 guests