Failover of 2 or More Internet Circuits on Same Device

The rationale behind this design was that the client required an auto failover solution from the ISP. The ISP is provisioning client with 4 Internet circuits over same physical Ethernet medium via separate VLANs. Two out of these four circuits have radio links as backups & traffic shifting mechanism is manual. Client was terminating all of these circuits on same router of theirs & had PBR applied along with IP SLA (obviously, default route can’t be the option in case of multiple Internet links). 

At ISP side, PBR & IP SLA couldn’t be applied as the PE router was not the same for both primary & backup media. So, I used multiple techniques to fulfill client’s requirement keeping in view the ISP’s design too.

I used IP SLA & PBR at client end to failover between primary & secondary links so that traffic destined for Internet could take the appropriate path out. BGP was configured between ISP & Client device so that return traffic could take the appropriate path (same as outgoing) into client’s device.

Gear Used:

GNS3 (Intel Core i3 3110M with 4 GB  RAM)

Cisco C3640-JK9O3S-M, Version 12.4(16a)

NOTE: Live IPs used in this implementation are purely fictitious; any resemblance to any IP living or dead is purely coincidental.

Network Diagram:

Scenario Detail:

• ·         Client has been assigned two 110.2.158.16/28 & 103.223.161.128/28 live IP pools by the ISP for the two separate links.  
• ·         The 2 Internet links have been separated by VLANs 98 & 99 over the Primary media.
• ·         Backup links are physically separate & are connected to different Ethernet ports of client’s router.
• ·         BGP neighbor ship has been established over all four point to point connections.
• ·         MED has been configured higher on backup links so that return traffic will follow the backup path in case of primary media outage.
• ·         Route maps have been applied at ISP side on all neighbors so that any given link allows only the traffic of assigned subnet.
• ·         At client end, PBR has been applied along with IP SLA tracking.
• ·         Traffic from subnet 110.2.158.16/28 will route to 100.100.100.13 & in case this hop becomes unavailable, then, the traffic will route to backup next hop 100.100.100.21.
• ·         Traffic from subnet 103.223.161.128/28 will route to 100.100.100.17 & in case this hop becomes unavailable, then, the traffic will route to backup next hop 100.100.100.25.
• ·         The above two rules will also apply to return traffic.

    Configuration Files:

    http://www.4shared.com/office/6sQJ7DJM/Failover_of_2_or_More_Internet.html