Dual ISP Connections on Single Router

[Raymond Brown]

Is this possible??

Scenario:  I have 1 router (RT1) with 2 ISP connections Interface1 - Verizon & Interface 2 - Comcast. I have 2 vlans on my internal network, Vlan10 and Vlan20.  I want all traffic from Vlan 10 to go out to the internet via Interface1 on Verizon's line and all traffic from vlan20 out interface 2 via Comcast.  If Interface 1 goes down I want all traffic for Vlan10 to failover to interface 2 & vice versa with interface 2 going down.

Attached is an example of the topology I am trying to accomplish.

[Hitesh Vinzoda]

Assuming your VLAN interfaces are on the edge router

You can use below configuration for reference

access-list 1 permit vlan10_NETWORK VLAN10_NETMASK
access-list 2 permit vlan20_NETWORK VLAN20_NETMASK
!
interface vlan10
ip policy route-map IA_ACCESS_10

interface vlan20
ip policy route-map IA_ACCESS_20
!
route-map IA_ACCESS_10 permit 10
match ip address 1
set ip next-hop <GW_IPADDRESS_OF_ISP01>
!
route-map IA_ACCESS_10 permit 20

route-map IA_ACCESS_20 permit 10
match ip address 2
set ip next-hop <GW_IPADDRESS_OF_ISP02>
!
route-map IA_ACCESS_20 permit 20

TIA

Hitesh

[Raymond Brown]

Thank You Hitesh. 

I do not see in this configuration what will allow the interface to failover.  Say for instance if ISP02 goes down, how will interface vlan20 know to route traffic to ISP01?  I am fairly new to Cisco, would you mind kind of explaining what these commands are doing?

[Mark Malone]

Hi

take a look at this doc , its explained in this , you need to use ip sla with your route-maps to track for failover , same concept your trying to achieve

http://www.firewall.cx/cisco-technical-knowledgebase/cisco-routers/861-cisco-router-pbr-ipsla-auto-redirect.html

Or

https://letusexplain.blogspot.com/2014/04/ip-sla-tracking-configuration-with.html

[paul driver]

Hello
You mention what routing process your using, (static or dynamic)
With static routing, Htiesh is correct this can be performed by PBR however unless both your isps are aware of what your doing then you'll most certainly you'll get asymmetric routing which isn't a bad thing.

If your using say something dynamic routing such as BGP, then you can probably get a more deterministic result with using BGP path attributes such as (weight for outbound and as-path pending for inbound traffic)

res
Paul

[Richard Burts]

Paul makes a good point that we do not know whether the original poster is planning static routing or dynamic routing (though with 2 ISP many people would suggest that BGP dynamic routing was the optimum choice). And Mark makes a very good point that the route map will need to use verify-availability/IP SLA to achieve failover for PBR. Here is a link with some explanation and an example of using verify-availability.

While I do agree that the best solution for this is to use PBR I do not believe that it is necessary to have two route maps and two sets of PBR logic. I would suggest an approach like this:

- set up the routing environment (whether static or dynamic) so that one ISP is preferred and that traffic will fail over to the other ISP if there is a problem with the preferred ISP. (for this discussion let us assume that Verizon is preferred and Comcast is backup)

- that takes care of part of the requirements: vlan 10 will use Verizon and if there is a problem then vlan 10 will use Comcast.

- configure PBR for vlan 20. In the PBR logic the access list will match the addresses used by vlan 20 and will set ip hext hop to use Comcast and will specify verify-availability.

- this step addresses the other requirement that vlan 20 use Comcast and will failover to Verizon if there is a problem with Comcast.

There is another aspect of this which needs to be addressed - what address space is used and does it require address translation. And if it needs address translation how does the address translation handle failover? Does the original poster have provider independent address space? Does the original poster have address space from Verizon, address space from Comcast, or address space from both. When we know what address space is used we may be able to address the requirements for address translation.

HTH

Rick