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Step-by-Step Configuration and Troubleshooting Best Practices for the NGFW, NGIPS and AMP Technologies A Visual Guide to the Cisco Firepower Threat Defense (FTD)
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Dual ISP connections ASA5500



Re: Dual ISP connections ASA5500

see this

few people have raised same question!

You can have redundant or backup link or if you have multiple context you can have active/active depending on how you setup your context or have a router infront of the ASA doing PBR..

Community Member

Re: Dual ISP connections ASA5500


Please look at the following:

Terminating two ISPs on ASA/PIX-

ISP1------------------Internet |

| |

| |

| | |




Internal Network

Lets say we has above setup, with ISP1 being the Primary ISP

and ISP2 being the Secondary ISP.

I'm assuming that you all know how ISP failback is configured and

how it functions. To summarize, in ISP failback all traffic goes out

using ISP1 and if it fails, ASA/PIX starts routing traffic via ISP2.

Scenario I


Now, we do not want to configure ISP failback, but we needs

to route Web (port 80,443) traffic via ISP2 and all other traffic

via ISP1. This requires PBR, which is not supported on ASA/PIX, but

we can configure a workaround on ASA/PIX to make it work.

Following are the commands which will achieve it-

route ISP1 0 0 //Default route pointing to ISP1

route ISP2 0 0 2 //Default route with Metric 2 via ISP2

static (ISP2,inside) tcp 80 80

static (ISP2,inside) tcp 443 443

sysopt noproxyarp inside

nat (inside) 1 0 0

global (ISP1) 1 interface

global (ISP2) 1 interface

Thats it !! Now all the traffic destined to any address on port 80/443

will be forcibly put on ISP2 interface and routed from there.

Note: This stuff requires that we KNOW what the destination ports are,

if there is some traffic which uses dynamic ports, like voice traffic

we will have to route it via ISP1 and cannot make it route via ISP2.

Scenario II


In the same setup, if we say that we wants half traffic to go

via ISP1 and half traffic via ISP2, first we need to understand

that ASA is NOT a load-balancer or packet-shaper. Hence we cannot

*truly* achieve this, but we may configure ASA in such a manner that

traffic for some destination IP address is routed via ISP1 and some

is routed via ISP2. Following would be configuration commands in this


nat (inside) 1 0 0

global (ISP1) 1 interface

global (ISP2) 1 interface

route ISP1

route ISP2

The first creates a default route that routes addresses with the first

bit of 1 to of ISP1.

The second creates a default route that routes addresses with the first

bit of 0 to of ISP2.

Note: This will do traffic routing based on *Destination* IP addresses and

NOT based on traffic load. As I mentioned, ASA is NOT a packet-shaper.

Hope this helps!



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