Method, device, and system for providing hot reservation for in-line deployed network functions with multiple network interfaces

A system comprising:

• a first Network Function (NF) unit, connected to an ingress router and to an egress router;
• a second NF unit, connected to said ingress router and to said egress router;
• wherein the first NF unit is initially configured as a controlling NF;
• wherein the second NF unit is initially configured as a backup NF;
• wherein the first NF unit, operating as the controlling NF, periodically sends an ingress-bound keep-alive message to said ingress router, wherein said ingress-bound keep-alive message triggers said ingress router to send a first response message to the second NF unit operating as the back NF;
• wherein the first NF unit, operating as the controlling NF, periodically sends an egress-bound keep-alive message to said egress router, wherein said egress-bound keep-alive message triggers said egress router to send a second response message to the second NF unit operating as the back NF;
• wherein the second NF unit, operating as the backup NF, is to automatically trigger a switchover in which (i) said first NF unit is switched to being the backup NF and (ii) said second NF unit is switched to being the controlling NF, if the second NF unit did not receive, for at least a pre-defined time-period, at least one of:
• (I) the first response message from the ingress router, (II) the second response message from the egress router.