Author Archive: Jason Mathews

July 26, 2012

Global IP Addresses - What Are They and How Do They Work?

SoftLayer recently released "Global IPs" to a good amount of internal fanfare, and I thought I'd share a little about it with the blog audience in case customers have questions about what Global IPs are and how they work. Simply put, Global IP addresses can be provisioned in any data center on the SoftLayer network and moved to another facility if necessary. You can point it to a server in Dallas, and if you need to perform maintenance on the server in Dallas, you can move the IP address to a server in Amsterdam to seamlessly (and almost immediately) transition your traffic. If you spin up and turn down workloads on cloud computing instances, you have the ability to maintain and a specific IP address when you completely turn down an environment, and you can quickly reprovision the IP on a new instance when you spin up the next workload.

How Do Global IPs Work?

The basics of how the Internet works are simple: Packets are sent between you and a server somewhere based on the location of the content you've requested. That location is pinpointed by an IP address that is assigned to a specific server or cloud. Often for various reasons, blocks of IP addresses are provisioned in one region or location, so Global IPs are a bit of a departure from the norm.

When you're sending/receiving packets, you might thing the packets "know" the exact physical destination as soon as they're directed to an IP address, but in practice, they don't have to ... The packets are forwarded along a path of devices with a general idea of where the exact location will be, but the primary concern of each device is to get the all packets to the next hop in the network path as quickly as possible by using default routes and routing tables. As an example, let's follow a packet as it comes from an external webserver and detail how it gets back to your machine:

  1. The external webserver sends the packet to a local switch.
  2. The switch passes it to a router.
  3. The packet traverses a number of network hops (other routers) and enters the Softlayer network at one of the backbone routers (BBR).
  4. The BBR looks at the IP destination and compares it to a table shared and updated with the other routers on SoftLayer's network, and it locates the subnet the IP belongs to.
  5. The BBR determines behind which distribution aggregate router (DAR) the IP is located, then it to the closest BBR to that DAR.
  6. The DAR gets the packet, looks at its own tables, and finds the front-end customer router (FCR) that the subnet lives on, and sends it there.
  7. The FCR routes the packet to the front-end customer switch (FCS) that has that IP mapped to the proper MAC address.
  8. The switch then delivers the packet through the proper switchport.
  9. Your server gets the packet from the FCS, and the kernel goes, "Oh yes, that IP on the public port, I'll accept this now."

All of those steps happen in an instant, and for you to be reading this blog, the packets carrying this content would have followed a similar pattern to the browser on your computer.

The process is slightly different when it comes to Global IP addresses. When a packet is destined for a Global IP, as soon as it gets onto the SoftLayer network (step 4 above), the routing process changes.

We allocate subnets of IP addresses specifically to the Global IP address pool, and we tell all the BBRs that these IPs are special. When you order a global IP, we peel off one of those IPs and add a static route to your chosen server's IP address, and then tell all the BBRs that route. Rather than the server's IP being an endpoint, the network is expecting your server to act as a router, and do something with the packet when it is received. I know that could sound a little confusing since we aren't really using the server as a router, so let's follow a packet to your Global IP (following the first three steps from above):

  1. The BBR notes that this IP belongs to one of the special Global IP address subnets, and matches the destination IP with the static route to the destination server you chose when you provisioned the Global IP.
  2. The BBR forwards the packet to the DAR, which then finds the FCR, then hands it off to the switch.
  3. The switch hands the packet to your server, and your server accepts it on the public interface like a regular secondary IP.
  4. Your server then essentially "routes" the packet to an IP address on itself.

Because the Global IP address can be moved to different servers in different locations, whenever you change the destination IP, the static route is updated in our routing table quickly. Because the change is happening exclusively on SoftLayer's infrastructure, you don't have to wait on other providers propagate the change. Think of updating your site's domain to a new IP address via DNS as an example: Even after you update your authoritative DNS servers, you have to wait for your users' DNS servers to recognize and update the new IP address. With Global IPs, the IP address would remain the same, and all users will follow the new path as soon as the routers update.

This initial release of Global IP addresses is just the tip of the iceberg when it comes to functionality. The product management and network engineering teams are getting customer feedback and creating roadmaps for the future of the product, so we'd love to hear your feedback and questions. If you want a little more in-depth information about installation and provisioning, check out the Global IP Addresses page on KnowledgeLayer.

-Jason

Subscribe to Author Archive: %