Tracking with dual ISP

[Harutyun Hakobyan]

Hi all,

I have two static routes with tracking and second one with AD 5 (only one route must be in routing table):

ip route Destination_IP 255.255.255.255 Next_hop_ISP_1 track 100
ip route Destination_IP 255.255.255.255 Next_hop_ISP_2 5 track 200

This is track and SLA configs:

!
track 100 ip sla 100 reachability
 delay down 5 up 5
!
track 200 ip sla 200 reachability
 delay down 5 up 5
! 

!
ip sla 100
 icmp-echo Next_hop_ISP_1 source-interface Interface_with_ISP_1_IP
 frequency 5
ip sla schedule 100 life forever start-time now
!
ip sla 200
 icmp-echo Next_hop_ISP_2 source-interface Interface_with_ISP_2_IP
 frequency 5
ip sla schedule 200 life forever start-time now
!

#sh ip route track-table
 ip route Destination_IP 255.255.255.255 Next_hop_ISP_1 track 100 state is [up]
 ip route Destination_IP 255.255.255.255 Next_hop_ISP_2 5 track 200 state is [up]

However I had situation when track 100 was up but I hadn't connection to Destination_IP, i.e. I had connection to ISP_1 but ISP_1 hadn't connection to Destination_IP. In that case route to Destination_IP remained with ISP_1 and didn't change to ISP_2.

So how to solve this problem  - if through ISP_1 Destination_IP is unreachable change to ISP_2 and in routing table always have one route to Destination_IP (no load balancing) ?

Thanks

[Vasilii Mikhailovskii · Accepted solution]

Hello.

If you want to track reachability of remote IP-address (let's say 8.8.8.8), you need to adjust configuration:

1. In ip sla use icmp-echo to 8.8.8.8 with apropriate source ip-address.

2. Then configure local PBR to send traffic from ISP1's interface via ISP1 and from ISP2's interface via ISP2.

3. Profit.

PS: this configuration might be a challenge if you use dynamic IP-address on WAN-facing interfaces.

[Harutyun Hakobyan]

Dear Vasilii Mikhail,

Thank you very much !!!