This answer differs slightly depending on whether you are talking about the monitoring interface or the command and control interface.
If both the Routers are connected to the same hub or switch then the sniffing interface would be receiving packets from the hub or switch (via span) regardless of which router is in use. So only a single sensor would be needed.
If, however, the routers are connected to different switches then in most cases you would need 2 sensors (one for each switch).
Command and Control Interface:
IS the sensor commicating to CSPM or Unix Director through the routers? If not (i.e. CSPM or Unix DIrector are on same net as sensor command and control) then the switching of the routers won't make a difference on communicating with CSPM or Unix Director.
If the sensor is communicating with CSPM or Unix DIrector through the router then it becomes a question of how the backup was implemented. If the routers are sharing a common ip address so all machines can set that ip address as the default route then the sensor won't care which router is active.
If, however, the routers have different ips and all machines have to know about both routers then you get a strange situation. There may be away to setup a second route within the sensor to accomplish this.
The easiest way to determine this is to find out how the other machines are configured that are using the routers to route their traffic.
As for having the sensor manage the routers, then that is easy because one sensor can manage both routers.
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...