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ASR 1000 Multiple ISP Load Balancing

Rising star
Rising star

I came up with a few ideas to Load Balance based on multiple ISPs. In our network setup we have a distribution layer of 3750s going to an

ASR 1000 Series Router, which goes out to multiple ISPs, ISP1 and ISP2.

So let's say we also have a virtual fortinet appliance behind the 3750. If I say all traffic going to 0 - 126 goto ISP1, and 128 - 254 goto ISP2,

and then obviously whatever NATd IP the customer has (ISP1 or ISP2), the return traffic will have to go to that specific IP. The traffic will all

go back to the virtual fortinet on the same interface, so I would assume I would be safe with uPF.

I don't know of any ways to load balance based on Link Optimization, without implementing a load balancer, unless anyone has any other ideas.

I was just trying to find the best way to do a 50/50 split, which I know may not always be the case.

I just dont' want to pay for two 100Mbps links and only use one, seems like a waste of money.

5 Replies 5


Are you contemplating this because you haven't got any Provider Independent addressing?

Yes sir.

Why not pursue PI addressing then? If you're ever going to do it with IPv4 then now is possibly your last chance. I'm in Europe where the RIR (RIPE NCC) has announced on their website that IPv4 PI addressing is no longer available due to the global address shortage. However, two carriers have assured me they can still get some. That's if they are paid to manage the application of course.

Sudeep Valengattil
Cisco Employee
Cisco Employee

Hi John,

You can aply a route-map on ASR ingress interface.  Based the source address, you can set the next-hop to either ISP1 or ISP2. 

This 0-126 and 128-254, is ths the public to which the Internal IPs are getting NATed? Can u pls confirm?  Also confirm where do u apply the NAT


Well, I was pondering on seting a route to to out ISP1, out ISP2.

But, when I come to think of it, I would have to edit out certain routes pointed to inside our network from one of the ISPs.

NAT is perforemd by the virtual fortinet

Virtual Fortinet -> 3750 -> ASR -> ISP1|ISP2

Just trying to figure out the best way to load balance, since I don't have Provider Independent Addresses.

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