We have a site to site VPN, with split tunneling, between a branch office and headquarter. The VPN is used to extend Active Directory (AD) infrastructure to the branch office. The split tunneling ensures that only AD and DNS traffic from the branch office goes through the VPN. All other traffic, such as web, do not go through the VPN. The DHCP pool on the branch office router is configured as follows:
ip dhcp pool client
dns-server AD_DNS1, AD_DNS2, ISP_DNS1, ISP_DNS2
When the VPN is up, client computers at the branch office would use the Active Directory DNS servers. When the VPN goes down, client computers would use ISP's DNS. From the users' point of view, everything is fine. This all happens automatically.
Let's say we do not want to use the split tunneling anymore. Is there a way to configure the branch office router such that all traffic would flow through the VPN when the VPN is up, and all traffic would go through ISP when VPN is down?
I think you want to configure your ISP link as back up link and VPN as the primary one. The below URL explains with an example of static route tracking allows the security appliance to use an inexpensive connection to a secondary Internet service provider (ISP) in the event that the primary leased line becomes unavailable.
In order to achieve this redundancy, the security appliance associates a static route with a monitoring target that you define. The service level agreement (SLA) operation monitors the target with periodic Internet Control Message Protocol (ICMP) echo requests. If an echo reply is not received, the object is considered down, and the associated route is removed from the routing table. A previously configured backup route is used in place of the route that is removed. While the backup route is in use, the SLA monitor operation continues to try to reach the monitoring target. Once the target is available again, the first route is replaced in the routing table, and the backup route is removed.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...