Dual ISP - Cisco ASA HA Active/Standby

March 12, 2019·

So a single ISP isn’t cutting it anymore you need a backup just in case the primary fails and might as well add a second ASA into this design, more redundancy equals more up-time, right? On paper it sounds good but in the “real” world there probably is tipping point, more redundancy increases complexity. In this post we’ll aim to keep it simple, with setting up a Cisco ASA HA active/standby pair and then add in the second ISP. Let’s get started! So this is what our topology will look like all said and done, we have two firewalls and two different ISPs. The primary ISP is ISP-1 and the secondary ISP is ISP-2. We will always be using ISP-1 as the primary and won’t be load balancing between the two. ISP-2 will only be used when ISP-1 goes offline. When ISP-1 comes back online we will switch back over to ISP-1.

ASA-HA

So let’s first look at getting the ASA HA pair setup. In this example I have two ASA’s that are the same hardware and software version, For the HA I have to be able to use two interfaces for the LAN failover and State link interface. I need to choose one ASA that will be the primary and one that is secondary. If you already have a configuration on one ASA, choose that as the primary. The secondary ASA just needs enough configuration so that you can get into it as the configuration gets overwritten on the secondary ASA from the primary.

ASA-HA-1(config)# failover
ASA-HA-1(config)# failover lan unit primary

Move to the secondary ASA

ASA-HA-1(config)# failover
ASA-HA-1(config)# failover lan unit secondary

Now I need to configure the interfaces each ASA will be using two interfaces and they are connected directly to each other. Configuration is the same across the two ASAs with the exception of the IP address make sure they are different and are in the same network. I like to use a completely different range of IP addresses that are not in my network or public IP networks, otherwise you get into trouble. ;) In this example I’m using the link local address RFC 3927.

ASA-HA-1(config)# failover lan interface FAILOVER GigabitEthernet0/3
ASA-HA-1(config)# failover key password
ASA-HA-1(config)# failover link STATELINK GigabitEthernet0/4
ASA-HA-1(config)# failover interface ip FAILOVER 169.254.255.1 255.255.255.252 standby 169.254.255.2

Once you have configured both ASAs the primary will sync its configuration to the secondary and you will now have an active/standby pair of ASAs. You can verify the status by issuing the command show failover. We now need to switch gears and configure our secondary ISP and modify the primary ISP interface (OUTSIDE-ISP-1). On the primary ISP we need to configure a standby IP address on the interface and it needs to be on the same network. So in this example the standby IP is going to be 198.51.100.5 which was available to use from our primary ISP. We also need to do the same thing on the our secondary ISP interface (OUTSIDE-ISP-2. In this example the IP address is 198.51.100.140. Below is running configuration for that, this would be synced to both firewalls since they are now in an HA pair.

interface GigabitEthernet0/0
nameif OUTSIDE-ISP-1
security-level 0
ip address 198.51.100.10 255.255.255.128 standby 198.51.100.5
!
interface GigabitEthernet0/1
nameif OUTSIDE-ISP-2
security-level 0
ip address 198.51.100.135 255.255.255.128 standby 198.51.100.140
!

Once that is done we now need to configure these ASA’s to only use the primary ISP. If the primary ISP fails we switch over to the secondary ISP, we are not load balancing between the two, its one or the other. To do that we need to track the route. On this network we have a default static route that points to the primary ISP’s next hop address. In this example that is 198.51.100.1 the command to track that route.

ASA-HA-1(config)# route OUTSIDE-ISP-1 0.0.0.0 0.0.0.0 198.51.100.1 1 track 1

This does not do anything yet, we are close but we also need to add another default route and point that to the secondary ISP.

ASA-HA-1(config)# route OUTSIDE-ISP-2 0.0.0.0 0.0.0.0 198.51.100.129 254

Notice that I’m putting a distance metric on this route, this has a higher metric than the first default route so it won’t be used until the primary route fails.

The track command will remove the primary route if it fails and then the ASA will install this the route in the routing table to switch over to the secondary ISP. We still have to configure some additional settings in order for this to work. We need to create an SLA on the ASA, in this example I’m using Google’s Public DNS as a reachability test. If this was production setup I would probably use a system that I own instead of relaying one somebody else.

ASA-HA-1(config)# sla monitor 10
ASA-HA-1(config)# type echo protocol ipIcmpEcho 8.8.8.8 interface OUTSIDE-ISP-1 
ASA-HA-1(config)# num-packets 5
ASA-HA-1(config)# frequency 10

Create the schedule and reference the sla monitor number. We want this run forever (as long as the hardware lives) and we want to start it now.

ASA-HA-1(config)# sla monitor schedule 10 life forever start-time now

We finally can create a track on this route

ASA-HA-1(config)# track 1 rtr 10 reachability

If we look at show route we can see we are using the primary ISP

show  route
 
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, V - VPN
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, + - replicated route
Gateway of last resort is 198.51.100.1 to network 0.0.0.0
 
S*       0.0.0.0 0.0.0.0 [1/0] via 198.51.100.1, OUTSIDE-ISP-1
C        169.254.255.0 255.255.255.252 is directly connected, FAILOVER
L        169.254.255.1 255.255.255.255 is directly connected, FAILOVER
C        192.168.2.0 255.255.255.0 is directly connected, INSIDE
L        192.168.2.50 255.255.255.255 is directly connected, INSIDE
C        198.51.100.0 255.255.255.128 is directly connected, OUTSIDE-ISP-1
L        198.51.100.10 255.255.255.255 is directly connected, OUTSIDE-ISP-1
C        198.51.100.128 255.255.255.128 is directly connected, OUTSIDE-ISP-2
L        198.51.100.135 255.255.255.255 is directly connected, OUTSIDE-ISP-2

If that link fails or if the reachability fails the ASA will change over to the secondary ISP. Looking at the show route confirms this

ASA-HA-1# show route
 
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, V - VPN
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, + - replicated route
Gateway of last resort is 198.51.100.129 to network 0.0.0.0
 
S*       0.0.0.0 0.0.0.0 [254/0] via 198.51.100.129, OUTSIDE-ISP-2
C        169.254.255.0 255.255.255.252 is directly connected, FAILOVER
L        169.254.255.1 255.255.255.255 is directly connected, FAILOVER
C        192.168.2.0 255.255.255.0 is directly connected, INSIDE
L        192.168.2.50 255.255.255.255 is directly connected, INSIDE
C        198.51.100.0 255.255.255.128 is directly connected, OUTSIDE-ISP-1
L        198.51.100.10 255.255.255.255 is directly connected, OUTSIDE-ISP-1
C        198.51.100.128 255.255.255.128 is directly connected, OUTSIDE-ISP-2
L        198.51.100.135 255.255.255.255 is directly connected, OUTSIDE-ISP-2

That’s all I got for this one, being able to switch between ISP automatically depending on reachability is an easy way to add additional redundancy, we don’t have to have to two ASA’s you could do this if you only had one ASA with two ISPs. I hope this information is helpful

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