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DaneelOlivaw200
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Joined: Wed Sep 21, 2022 3:07 am

IP SLA with BGP Routing

Thu Mar 16, 2023 4:32 pm

Hi all.

So, currently, the topology looks something like this:


ISP1***************ISP2
|********************|
eBGP*************eBGP
|********************|
RTR-1 <--iBGP--> RTR-2
|********************|
| ---------LAN------- |

Please disregard the asterisks. I couldn't use spaces to format the topo properly, so I used asterisks to separate them :).

Both ISPs advertise a default route.

Let's say one has a problem advertising the inside routes upstream for some reason. I want to setup some kind of IP SLA where if ping to something like 8.8.8.8 is not reachable from the local router, it uses the backup 0.0.0.0/0 address advertised by the iBGP peer.

So let's say VRRP is setup for a client on the LAN to RTR-1.

Client -> RTR-1 -> ISP-1.

Then let's say ISP-1 has an issue upstream.

I want that RTR-1 then to use the default route being advertised by RTR-2 (Which comes upstream from ISP-2 and default-originate is enabled).

Client -> RTR-1 -> RTR-2 -> ISP-2

Then, when the SLA is able to ping 8.8.8.8 again, use its local route.

How would you go about doing this in ROS 7.x?
 
wiseroute
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Posts: 352
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Re: IP SLA with BGP Routing

Sun Mar 19, 2023 3:57 pm

hello
Client -> RTR-1 -> RTR-2 -> ISP-2

Then, when the SLA is able to ping 8.8.8.8 again, use its local route.

How would you go about doing this in ROS 7.x?
i don't think it's about ros v7. and probably not about ebgp upstream either.

but, your ebgp, ibgp and vrrp combo make things unnecessary complex. and I don't see any benefits. vrrp is for lan redundancy. and bgp has its own mechanism.

afaik, direct ibgp peering between 2 edge routers will lead to split brain for the lan side or for your vrrp setup. it won't be easy.

hmm.. 2 vrrp group :
the 1st, master for isp1 via rtr1.
the 2nd, master for isp2 via rtr2.

need a 3 bgp router as a bgp rr. to overcome that split brain, and being the vrrp gateway.

but if you put ebgp1 and vrrp1 and so forth all in one box, the forwarding process is obvious. since vrrp only works for physical error.

just a thought. good luck 👍🏻
 
DaneelOlivaw200
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Joined: Wed Sep 21, 2022 3:07 am

Re: IP SLA with BGP Routing

Sun Mar 19, 2023 4:12 pm

Yes, there is already redundancy to some degree. Agreed!

Let me dig in a bit though to provide some context around what I'm looking to do.

Let's outline a few networks here.

22.22.22.0/30 (Peer link from Rtr-1 to ISP-1)
33.33.33.0/30 (Peer link from Rtr-2 to ISP-2)
13.14.15.0/24 (Internal subnet with Rtr-1 as Active VRRP member).

So, I've seen cases where one ISP has short periods of missing the route 13.14.15.0/24 upstream. As in, a client 13.14.15.20 can get out, but can't get back.

So, someone in New York can't get back, but somewhere in Georgia doesn't have that problem.

What I want to do is ping from the 13.14.15.2/24 address on RTR-1 to an obviously public IP like 8.8.8.8. If there is a timeout after 10 seconds, I want RTR-2 to prefer the default route advertised by RTR-2 to RTR-1 via the crossconnect.

Is this possible? If I need to use static routes to do that, that's understandable.

This is a rare occurence, but I've seen it happen twice over about 3 years.
 
wiseroute
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Posts: 352
Joined: Sun Feb 05, 2023 11:06 am

Re: IP SLA with BGP Routing

Sun Mar 19, 2023 4:30 pm

hi.
As in, a client 13.14.15.20 can get out, but can't get back.
disagree.

imho. any public ip blocks from both isp, if any, still can go both outside nor inside your network via either one of the isp, provided that you made those blocks advertised through your ebgp router, as long as the either rtr1 or rtr2 whose ip blocks belongs to are not physically dead. if it is dead then your internal ip blocks will not be advertised in your ibgp network. which lead to dead route as well.

static is not relevant because it will make your setup even more complex.
 
DarkNate
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Re: IP SLA with BGP Routing

Thu Mar 23, 2023 7:35 am

IP SLA is a fancy term created by Cisco.

In Linux world we call this recursive routing, you can use recursive routing. But MikroTik has Netwatch tool to make your life easier, use it with some basic scripting and you're good to go.

Set up test for TCP to google.com or whatever.

FYI: RouterOS is 100% Linux.
 
wiseroute
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Re: IP SLA with BGP Routing

Thu Mar 23, 2023 7:58 am

@darknate,

In Linux world we call this recursive routing, you can use recursive routing. But MikroTik has Netwatch tool to make your life easier, use it with some basic scripting and you're good to go.
well, yes. maybe that will be a good option if the @op routing environment was static.

the problem is it wasn't.
So, I've seen cases where one ISP has short periods of missing the route 13.14.15.0/24 upstream. As in, a client 13.14.15.20 can get out, but can't get back.
if the upstream has missing route, then the missing ip block as good as unusable.

hence the @op wanted to do some ebgp routing to overcome this missing route to be reachable via the other upstream.

but, even ebgp has minimum ip space to be advertised.

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