Virtual IP (VIP)

2.1 Explain characteristics of routing technologies

📘CompTIA Network+ (N10-009)

A Virtual IP (VIP) is an IP address that does not belong to a single physical device. Instead, it is shared among multiple devices to improve availability, redundancy, and load balancing in a network.

VIPs are commonly used in servers, routers, and load balancers. They allow multiple devices to present a single IP address to clients, making the system more reliable and easier to manage.

Key Points to Remember for the Exam

Definition:
- A Virtual IP (VIP) is an IP address that can move between multiple devices or represent multiple devices as one on a network.
- VIPs are not tied to a single physical interface; they are logical addresses.
Purpose of VIPs:
- High Availability: If one device fails, another can take over the VIP, so clients don’t notice downtime.
- Load Balancing: VIPs can distribute client requests across multiple servers to avoid overloading a single device.
- Simplified Network Management: Clients only need to know one IP, even if multiple devices handle the traffic.
How VIPs Work:
- Imagine two or more servers behind a load balancer.
- The VIP is the IP address of the service clients connect to (like a web server or application server).
- The load balancer receives traffic sent to the VIP and forwards it to the actual physical servers (real IP addresses).
- If a server goes down, the VIP can be reassigned to another server automatically.
Common Scenarios in IT Networks:
- Load Balancing Web Servers: A VIP is assigned to a web service. Multiple servers serve the same website, and traffic is split among them. Clients always use the VIP to connect.
- High Availability Routers (FHRP): VIPs are used in protocols like HSRP, VRRP, and GLBP. The VIP represents the default gateway for clients. If one router fails, another takes over the VIP without clients noticing.
- Clustered Applications: Databases or application servers can share a VIP, so client applications always have a consistent IP to connect to, regardless of which physical server is active.
Protocols Using VIPs:
- HSRP (Hot Standby Router Protocol) – Cisco proprietary, for gateway redundancy.
- VRRP (Virtual Router Redundancy Protocol) – Open standard alternative to HSRP.
- GLBP (Gateway Load Balancing Protocol) – Combines redundancy with load balancing.
- Load Balancers – VIP points to a service distributed across multiple backend servers.
Important Exam Notes:
- VIP is logical, not tied to one device.
- VIP is commonly used in gateway redundancy and server load balancing.
- In redundancy protocols, the VIP is what client devices use as their default gateway, not the physical IP of any single router.
- VIP helps in fault tolerance and continuous network availability.

Simple Diagram for Understanding VIP

        Clients
          |
       [VIP: 192.168.1.100]
          |
    ----------------------
    |         |          |
  Server1   Server2    Server3
(real IPs: 192.168.1.101, .102, .103)

Clients only know the VIP (192.168.1.100).
Servers behind it handle the requests.
If Server1 fails, the VIP stays active via Server2 or Server3.

Exam Tip

When asked about VIPs, think:
“It’s an IP address that moves between devices or represents multiple devices to provide redundancy and load balancing.”
VIP is not the same as a physical IP – it’s logical and flexible.