In a previous blog post, I talked about some common Local Traffic Manager (LTM) features that get overlooked, which can easily increase security posture. In this post, I want to discuss one of the less-known features that is frequently neglected because you may not understand the benefits. This feature is OneConnect.

OneConnect is an awesome addition to any modern application that follows good code and RFC standards such as TCP or HTTP. OneConnect creates a pool of first time TCP connections to each pool member and makes them available for reuse by later connections. This is done by using TCP standards like idle timeouts, keepalives, etc.

When an initial connection is created to a pool member, the BIG-IP holds that connection open and uses it for other TCP flows that are destined for that member. This can drastically reduce the number of connections the web server has to process and allocate resources for, thereby improving the web server’s overall performance.

With an HTTP connection, OneConnect can manage HTTP connection flows and process them much the same way as TCP flows. It first manages the TCP flow for that connection like a TCP app. Because OneConnect is HTTP-aware, thanks to whichever HTTP profile you associated with the virtual server, it can read the HTTP flows and process state for them at the same time. If the TCP connection the HTTP flow was using ages out, when a new TCP flow is connected, it will continue that HTTP flow over the new TCP connection.

The LTM uses HTTP standards like keepalives to maintain state. In the case of non-HTTP/1.1 connections, there is no keepalive and the LTM will intercept “Connection:close headers” and transform them to “x-connection: close headers” so it can process connections the same way. This feature, OneConnect Transformations, has to be enabled in the HTTP profile.

By default, OneConnect makes every connection it processes available for reuse. You can restrict this in your OneConnect profile by changing the subnet mask. The subnet mask sets the groupings that OneConnect will make with the incoming IPs.

For example, maybe you don’t want external client IPs and internal client IPs sharing connections. In this case, you could change the mask to so that your 192’s or 10’s will not mix with 25s or 100s. Of course, if you are using 172.16.x.x internally, you need to use instead. Knowledge of your internal IP structure and your application requirements is important.

A note on SNAT: If you use SNAT Automap on your virtual server, OneConnect gets applied after SNAT; so no matter what your mask is, every flow will be reused regardless of the setting in the OneConnect profile. If you use a SNAT Pool, you could use a 32-bit mask to create more flows, but unless you have a really high connection count, there is no need to do this.

To help illustrate this, here is an example I worked on not long ago. One of the state governments I worked with had a web application that processed healthcare options for “Obamacare.” Day-to-day connections to the application hovered at about 4,000 to each server. When it came time for open enrollment, all of the web servers fell over trying to process more than 25,000 connections each. Users who got connected reported the server was so slow, it could not respond to page requests, and timed out. Once OneConnect was enabled with a default mask, the number of active connections dropped to about a 100 per server! The application bounced back completely, and the developers said the application worked better than in development.

There are some special considerations when utilizing OneConnect within your environment. The application has to use TCP standards for clearly defined flows. OneConnect will not work if your flows do not provide good headers for distinguishing source and destination. If your application is 20-years-old and home-grown, it might not work. Recent applications should not have issues.

Secondly, you are sharing TCP flows. If you are sniffing the wire to look at incoming web server traffic, you might not see the flow you are looking for because it was part of a reuse pool. In this case, try to match the client port. The port should remain the same most of the time, but since you are combining different flows from different IPs, the likelihood of overlap is higher. Also, if your application needs to see client IPs, you will need to enable “x-forward-for” and configure the web server to look at that header instead. Additionally, if you are doing SSL Passthru, this is not an option due to the traffic encryption. OneConnect requires termination. You would have to decrypt and then re-encrypt to the backend.

Lastly, one item of particular note is sizing. Since OneConnect can drastically mask a connection table, you need to incorporate the application’s client activity in with the web server connection load to get a feel for how many web servers you need. You might, over time, find out that you cannot turn OneConnect off because your load will be too much for the existing number of web servers you have.

I hope this post has piqued your interest in OneConnect and what your F5 LTM can do for you. There are many additional features beyond “load balancing” that can enhance your investment, increase your return on investment, and improve end-user experience. GuidePoint Security’s professionals, with years of multifaceted expertise, can meet with you to learn more about your organization’s requirements and help build a customized security plan to best meet your needs.

If you’re a GuidePoint client and have questions about OneConnect, please reach out directly to your personal contact or email us at If your organization is interested in learning more about OneConnect and if it’s the right tool for you, let us know. You can find out more about GuidePoint and our services at

About GuidePoint Security

GuidePoint Security LLC provides innovative and valuable cyber security solutions and expertise that enable organizations to successfully achieve their mission. By embracing new technologies, GuidePoint Security helps clients recognize the threats, understand the solutions, and mitigate the risks present in their evolving IT environments. Headquartered in Herndon, Virginia, GuidePoint Security is a small business, and classification can be found with the System for Award Management (SAM). Learn more at: