Routing
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Contributor
stnz
Posts: 29
Registered: ‎03-26-2010
0

Multiple IP monitors

[ Edited ]

Is there something like a preference value for the IP monitors?

 

With two ISPs everything is simple and nice, but what about adding a 3rd ISP to the mix? Basically, I have an SRX device with filter-based forwarding and IP monitoring configured to monitor two ISP gateways and do failover between them. If the other ISP is down, the default gateway of that routing instance is switched to the other ISP.

 

Now to the problem: If I wanted to add one more IP monitor which triggers when BOTH ISPs are down and switches to 3G connection how should it be done? Creating an IP monitor with a probe that triggers when both of the ISP gateways are down is trivial, but how does it coexist with the other IP monitors & probes that only monitor one gateway?

 

To clarify, what I want to do is: There are two normal ISP connections and a 3G connection. In a normal situation web browsing and some other traffic should be going through the faster but less reliable consumer ISP and the rest through the other ISP. If the other one goes down, the traffic is switched to the other one. But, if somebody manages to cut the outgoing fiber optics all traffic should be switched over to the 3G connection.

Distinguished Expert
dfex
Posts: 752
Registered: ‎04-17-2008
0

Re: Multiple IP monitors

[ Edited ]

It doesn't look like there is a preference value, but what you can do is specify multiple RPM-Probes in an ip-monitoring policy.  I haven't had a chance to lab this yet, but I suspect that each probe will be logically OR'ed so that until all probes fail your next hop won't be installed.  Add the following policy alongside your other two:

 

ip-monitoring {
    policy 3G-BACKUP {
        match {
            rpm-probe [ ISP-A-TEST ISP-B-TEST ];
        }
        then {
            preferred-route {
                route 0.0.0.0/0 {
                    next-hop <3G-Backup-route>;
                }
            }
        }
    }
}

I'd be interested to hear if it works

Ben Dale
JNCIP-ENT, JNCIS-SP, JNCIE-SEC #63
Juniper Ambassador
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Contributor
stnz
Posts: 29
Registered: ‎03-26-2010
0

Re: Multiple IP monitors

I would guess that all three IP monitors trigger when both two ISPs are down, and we end up having three default routes with the same preference value.. :smileytongue:

 

But yea, I could test what happens.

Distinguished Expert
dfex
Posts: 752
Registered: ‎04-17-2008
0

Re: Multiple IP monitors

[ Edited ]

No, the 3rd ISP only checks for the first two, and the first two only check for each other, so you'd only have a single default route pointing at your 3G interface.

 

Not that it matters - if you have all three ISPs down, none of the default routes are going to be needed.

Ben Dale
JNCIP-ENT, JNCIS-SP, JNCIE-SEC #63
Juniper Ambassador
Follow me @labelswitcher
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