Dynamic vs. Static IP AddressesAuthor: Ethan Ace, Published on May 12, 2012
While many cameras default to DHCP out of the box, that does not mean you should use it. This may seem basic for some, but those new to the industry may not know there are other options. In this note, we overview dynamic and static addressing, the advantages, disadvantages, and potential issues of each, and our recommendations for their use.
In summary, there are three key points to remember about addressing schemes:
- Do not use DHCP. There are few exceptions to this rule, but DHCP should generally only be used when staging cameras, not in the final installation.
- Do use static addresses. The potential headaches of dynamic addresses far outweigh the slight increse in configuration time required.
- DHCP address reservation provides the benefits of static addresses, but adds more configuration complexity. It should be used only when IT policy dictates, and systems may not deviate.
We review each of these items below, in more detail.
The most common type of dynamic IP address assignment is DHCP, which assigns addresses in a specified range to devices as they are requested, which is typically in the order the devices boot. DHCP servers are often built into even low-cost routers, or may be run as a service on most any Windows or Linux server. Most devices, including computers, cameras, routers, mobile devices, and more, default to DHCP from the factory.
The main benefit to using DHCP is a reduction in setup labor. Since installers do not need to connect to each camera to set its IP address, overall install time is decreased. The amount of time gained varies, however, as some manufacturers allow devices to be addressed in bulk, via their setup tool, using a specified range of IP address. In this case, the time savings are minimal.
However, there are key issues that users should be aware of before using DHCP:
- The possibility that addresses may change is the main drawback to using DHCP. When the device's lease expires, or when it reboots after power failure, there is a chance that its assigned IP address will change. This may present problems, as cameras which connect to the VMS via IP address (the vast majority) will no longer work until the camera is re-entered into the VMS system. Additionally, finding the updated address may be a nuisance, and may require the manufacturer's discovery tool.
- Another, less common when using dynamic addresses is the threat of rogue DHCP servers. Unauthorized DHCP servers may be plugged into the network, intentionally or unintentionally, and used to supply addresses. If set to a range other than what is expected on the network, devices may not be able to connect to servers, or IP address conflicts may arise. This is not normally a serious issue, however, as devices only seek a DHCP server when their lease expires, or upon boot.
Dynamic addressing is not recommended in any application. It may be acceptable in small systems, in which the VMS autodiscovers cameras or connects via MAC address despite IP address changes. However, this does not prevent issues connecting to the web interface, which is often needed when performing maintenance.
Dynamic Address Reservations
When using DHCP, specific devices addresses may be reserved by the server for specific devices, based on MAC address. This prevents the device's address from changing, eliminating the main drawback of using DHCP. To do so, the camera should be set for DHCP and the desired IP address and the camera's MAC address must be entered into the DHCP server's setup. Below is an example of the steps / interface for dynamic address reservation:
Assigning a static IP address to each camera is the most common way of handling IP camera addressing. In this method, a unique address is manually assigned to each camera, requiring no DHCP or other services.
Predictability is the key advantage to using static IP addresses. Since there is no chance of IP addresses changing, as with DHCP leases, the potential for connection issues is reduced, which may reduce troubleshooting time if issues arise.
The main drawback is the increased labor associated with assigning addresses to individual cameras. Static addresses are commonly assigned by individually connecting to each camera, either directly through the web interface, or via manufacturer-provided software. This may add a few minutes of installation time per camera, which can add up in large systems. Some manufacturer tools allow for batch addressing of cameras, so a selected group of cameras may be assigned IP addresses from a pre-defined range. Tools like this minimize the added time required.
Static addresses are generally recommended in all systems. The additional time required to enter addresses is minimal in small systems. In large systems, the extra time needed may be substantial, but no more than would be caused by troubleshooting after a single unexpected dynamic address change. Predictable increase in labor during installation is preferred to unpredictable troubleshooting time.
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