Azure IP Addresses

VIP –

  • Virtual IP means an IP that is visible externally but it may not be actually assigned to actual resource. So for example, if I have a web farm with two nodes, I don’t want IP of actual resources. Instead, I need an IP that can be used to identify my farm (both the nodes/VMs). Since it is not the IP that is actually allocated to the node, it is called virtual IP.
  • VIPs are always external facing. They are never internal and never assigned to the actual VM.
  • VIPs are always associated with CloudService/Load Balancer. Documentation uses the term CS and Load Balancer interchangeably. For example this article is about VIP on CS but inside it also says that it is associated with Load Balancer. On a side note, from IaaS perspective, load balancer will be more accurate term while from PaaS perspective CS will be better to visualize.

DIP –

  • Dynamic IP is the actual IP that a node/VM gets. These are actually assigned to the VM instance’s NIC card.
  • However, it is always internal. These IPs are assigned to the VM instance and are never available outside a CS/vNet within which the VM is present.
  • These are called Dynamic because by default, the IP that your VM gets can change if you deallocate.
  • In a typical scenario, let’s assume we have 10 VMs in a vNet, then each VM will get an internal IP (DIP) and “most of times” we don’t care even if it changes. Only in few scenarios we don’t want these internal IPs to change (say when your VM is hosting DNS). In that case, we would want this internal IP (DIP) to be static rather than dynamic. So, you could “reserve” these internal IPs as well. In a typical web farm scenario, you’d never care about reserving DIP.

ILPIP/PIP –

  • Public Instance-level IP (earlier called PIP) is an IP that is visible to external world AND is actually assigned to the VM instance.
  • So, they are same as VIP except that unlike VIP, they are actually assigned to VM instance.
  • If you access a VM using its PIP, the traffic never goes through load balancer. That is the reason why you never configure/add/delete any public endpoint (http/https etc.) on cloud service when you are using PIP because endpoints never come into picture.
  • In most of scenarios, you’d never want to use PIP. Some scenarios (like passive FTP) may be eligible candidate for using PIP.
  • You’d never use PIP for web farm scenarios as you will definitely have more than one VMs in your farm and you’d want traffic to be routed via load balancer. So for web farms, you’d want to use VIPs only.

Reserved/Stable IP:

  • These are one and the same. When you reserve an IP it becomes stable… doesn’t change irrespective of your deallocation of resources etc…. though deletion does affect even reserved IPs.
  • You can reserve both VIP and DIP but not PIP (again unless something changed).

-Rahul Gangwar
rg@outlook.in

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