Routing default traffic on a single link while two sla tracked links are active

[waheedullah Bahaduri]

Hello,

I have three (3) ISP connections (ISP1, ISP2, ISP3).
I want to set them up as following:

ISP-1 (primary) - to track Server-A (1.1.1.1) : untill the tracked server-A is active ALL traffic " any traffic " should be routed over this primary ISP-A link only

ISP-2 (secondary) - to track Server-B (2.2.2.2) : but should not route anything unless the primary link (Server-A) is down. When server-A is down then all traffic should be routed through this Secondary ISP.

ISP-3 (third) - track nothing but should be kept as last route

I configured two ip sla - tracking both ServerA & B over the two ISP1 & 2,, and added the (0.0.0.0 0.0.0.0) route on both of them , but the issue is that both the ISP1$2 are up same time and both ServersA & B are active same time, that way the traffic (default-Traffic) does not know which path to chose to route through.

Any suggestion please??

[Jon Marshall]

Your description is a little confusing because it sounds like you want to use ISP-1 until server-A is active but then you say you want to use ISP-2 if server-A is down. So I am assuming that if server-A is up then use ISP-1, if server-A is down but server-B is up then use ISP-2 and if both servers are down use ISP-3.

If so then all you need to do is increase the AD for the default routes. So ISP-1 has no AD configured which means if server-A is up it will be in the routing table. ISP-2 has an AD added and ISP-3 also has an AD which is greater than ISP-2's AD.

Which means if ISP-1 goes down then ISP-2's default route will be installed in the routing table because it has a better AD than ISP-3. And if both ISP-1 and ISP-2 are down then ISP-3 will be used.

Is this what you were looking for ?

Jon

[waheedullah Bahaduri]

No you are referring me to normal routing based in AD

Server-A is my PR-site, and is accessible only through the ISP1 which is an MPLS (data link)

Server-B is my DR-site and is accessible through ISP2 (internet link)

In this case, if Server-A is down then it does not matter to me if ISP1 is up or not because i can not reach my Server-B through isp1 which is mpls, i need to use isp2 to reach Server-B, and if isp-2 gets down then traffic should route through isp3

That is why i need to have sla tracking on isp1,isp2 and put the highest AD on my isp3

I did as following but this makes a the default traffic to lose its way, because both tracking destination servers (server-A & server-B) are available at the same time and thus default traffic can go through both routes. Rather all traffic should route only through isp1 if server-A is up and reachable, when it gets down the all traffic should pass through isp-2

Here what i did:

Ip sla 1
Icmp-echo 1.1.1.1 (Server-A)

Ip sla 2
Icmp-echo 2.2.2.2 (server-B)

Isp1(mpls):
Ip route 0.0.0.0 0.0.0.0 172.16.1.1 track 1

Isp2:
Ip route 0.0.0.0 0.0.0.0 180.88.33.49 track 2

Isp3:
Ip route 0.0.0.0 0.0.0.0 67.95.12.1 20

What i want is to switch the route to different isp based on tracking servers status, when server-A gets down traffic should be routed through isp-2 if even my isp-1 link is active

[Jon Marshall · Accepted solution]

I think what I suggested is what you want. I am using AD but together with IP SLA. So if server-A goes down then IP SLA will mark it as down and remove the default route pointing to ISP-1 from the routing table. If server-B is up it will then install the default route pointing to ISP-2. And if both servers are down it will use the default to ISP-3.

I did a quick lab and it worked as expected so unless I am still not understanding, all you need to do is add an AD to the ISP-2 default route which is less than the AD you added to the ISP-3 default route.

Jon

[waheedullah Bahaduri]

Thank you Jon, now it is working