# How Servers Share an IP Address for High Availability > Cisco's 2017 patent describes a system where multiple servers can share a single virtual IP address to ensure an application stays online even if one server fails. - **Patent:** US 9571603 - **Original title:** Redundancy network protocol system - **Owner:** Cisco Technology Inc - **Granted:** 2017 - **Status:** Active - **Times cited:** 4 - **Field:** telecommunications, software, consumer_electronics ## What it does This patent details a system where servers work together to keep an application running. A 'profile' for an application is shared between servers, and this profile includes a virtual IP address (VIP) that clients use to connect. Each server has a 'priority' level. The system automatically picks the server with the highest priority to handle client requests. If the active server fails, another server with a high enough priority takes over. The system constantly checks if servers are still 'neighbors' by sending and receiving status messages. It also tracks how many other servers are sending status messages to each server. If the counts don't match, priorities might be adjusted. For example, if Server A is supposed to get status messages from 3 other servers but only gets them from 2, its priority might decrease. ## What it does NOT cover - Systems where servers are not at least one router hop away from each other. - Protocols that do not use a virtual IP address shared between servers. - Systems that do not involve comparing priorities between servers to select an active one. - Methods that do not monitor server health via status messages. - Applications that do not require high availability. ## The clever bit The innovation lies in how servers actively manage each other's status and priorities, even across multiple network hops. It's not just about one server failing, but about a dynamic system where servers collaborate to maintain a single point of access (the virtual IP) for an application, adapting to changing network conditions and server availability. ## Real-world examples 1. High-availability clusters for critical servers 2. Network load balancing solutions 3. Virtual IP address management in data centers ## Why it matters This patent is part of the foundation for ensuring critical applications and services remain accessible. It addresses the need for 'high availability' in networking, meaning services should be continuously operational. This is crucial for everything from online banking to cloud services, where downtime can be very costly. ## Frequently asked questions ### What does How Servers Share an IP Address for High Availability cover? Cisco's 2017 patent describes a system where multiple servers can share a single virtual IP address to ensure an application stays online even if one server fails. ### Who owns patent US 9571603? Cisco Technology Inc owns this patent, granted in 2017. ### When does this patent expire? This patent is expected to expire on September 17, 2033, when the invention enters the public domain. ### What is patent US 9571603 cited by? This patent has been cited by 4 later patents that build on its ideas. ### What problem does this patent solve? This patent is part of the foundation for ensuring critical applications and services remain accessible. It addresses the need for 'high availability' in networking, meaning services should be continuously operational. This is crucial for everything from online banking to cloud services, where downtime can be very costly. ### What does this patent NOT cover? Systems where servers are not at least one router hop away from each other. **Full plain-English explainer:** https://patentbrief.org/patent/us/9571603/redundancy-network-protocol-system **Original patent:** https://patents.google.com/patent/US9571603 --- _Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._ ## Related patents Semantically similar inventions in the PatentBrief corpus: - [How DNS Servers Route Web Traffic to the Least Busy Server](https://patentbrief.org/patent/us/6178160/load-balancing-of-client-connections-across-a-network-using-server-based-algorithms) — A method for balancing web traffic by having servers report their current workload to a DNS server, which then directs new users to the fastest available machine. - [How to Send Data Streams Independently Without Connection Overload](https://patentbrief.org/patent/us/7904576/reliable-datagram-via-independent-source-destination-resources) — A method for sending multiple streams of data between devices using independent, reliable paths that keep data in the correct order without needing a constant connection. - [How Load Balancers Route Web Traffic Based on Specific Content](https://patentbrief.org/patent/us/5774660/world-wide-web-server-with-delayed-resource-binding-for-resource-based-load-balancing-on-a-distributed-resource-multi-node-network) — A method for web servers to route user requests to specific machines based on which files they store, rather than just blindly balancing traffic across all servers. - [How Distributed Servers Find Data Using Location Pointers](https://patentbrief.org/patent/us/7233978/method-and-apparatus-for-managing-location-information-in-a-network-separate-from-the-data-to-which-the-location-information-pertains) — A system that uses a network of specialized servers to track where specific data is located, allowing computers to find information by asking a server for its address rather than searching every machine. - [How Uber Manages Data Connections for Self-Driving Car Fleets](https://patentbrief.org/patent/us/10050760/uber-eats) — A system that splits network traffic for autonomous vehicles by sending heavy data over cheap channels while reserving a highly reliable channel specifically for delivery confirmations.