PEM: Subscriber-Aware Policy and Why Every Large Network Needs One

Previous post “PEM: Key Component of the  Next Generation University Network” provided a high-level overview of several Policy Enforcement Manager features which help K-12 Schools, Colleges and Universities transform their Networks into agile, user-focused “Data Delivery Fabrics” which redefine the way Educational Institutions provide data connectivity services to students, faculty, staff, and guests.

As with all networks, schools provide access to internal resources as well as the Internet. Typically, internal network (LAN) traffic is not a major concern for network admins (although at some point WiFi saturation prompts infrastructure expansion), but Internet link saturation is a much more common and serious issue. Since any expansion of Internet access is associated with increased ongoing operating expense (opex) and, in many cases, infrastructure expansion resulting in upfront capital expense (capex). Even when an institution can afford a larger ISP link, regional Internet service providers (ISPs) may not offer the required bandwidth, or the ISP lacks sufficient infrastructure to support and/or provide increased bandwidth resources.

Nobody likes slow Internet. From myriad apps constantly pulling data in the background to the always-connected lifestyle of millennial students, the need for a fast, reliable, and low-latency connection is now more critical than ever. In the environment with limited resources, such as a school’s ISP link, it is critical to have the ability to control and distribute these resources according to priorities which maximize user’s experience while still providing a healthy mix of QoS for different types of traffic. 

F5’s Policy Enforcement Manager (PEM) has a number of facilities to enable schools to achieve the optimal balance between performance and traffic priority. Policies, bandwidth controllers, traffic intelligence categories, and presets are among those facilities. Today we will talk about the core PEM functionality - Enforcement policies.

There are 3 main types of PEM Enforcement policies:

Pic 1. PEM Enforcement policy types

Global Policy: Applied to all users: known and unknown

Subscriber Policy: Applied to known users: provisioned statically or discovered via DHCP, Radius or Access Profiles & iRules

Unknown Subscriber Policy: Applied to unknown users

PEM uses various subscriber discovery methods which usually differ by implementation. RADIUS and DHCP “sniffing” are among the configurable discovery methods. 
When PEM sees traffic, it checks whether the source IP address belongs to any known user (previously-discovered subscriber). If the user is known, traffic is classified and appropriate action is taken according to Subscriber Policy of that user. However, if the source IP address is not known to PEM, the Unknown Subscriber Policy is used until that user is discovered. Global Policy is applied to all users and may contain high-level rules applicable to all users in the network (e.g. blocking of malicious URLs, suppression of certain P2P applications, etc.).


Pic 2. PEM Policies example

Each user can be assigned a Subscriber Policy, and as long as the user is known to PEM, all traffic associated with that user will be analyzed and given priorities according to the policy rules. Among other functions, rules are used to provide application visibility by categorizing both encrypted and unencrypted traffic into categories. URL filtering and blocking actions are also provisioned using PEM Policy rules.

PEM can associate a rule with the traffic using any of the following:

  • Classification
  • URL category
  • Flow
  • Custom


Pic 3. Policy rule Classification example


The Classification tab in enforcement policy rules has a flexible definition to match an Application or Category from the extensive list provided in drop-down menu. PEM uses signatures to detect the applications. These signatures are updated periodically by F5 and PEM can be configured to check for Signature updates automatically Daily, Weekly or Monthly.

Matching criteria can provide a positive or negative matching, allowing for granular actions like QoS/bandwidth control, reporting or TCP optimization to be applied to various classified traffic types.


URL category

Pic 4. URL categories and URLDB

URLs can be categorized according to pre-defined or custom definitions. PEM can also use external URLDB/Feed list which makes it easy to extend pre-defined Categories list and maintain central reference for Categorized URLs. URLDB is a CSV file that contains website URL and associated category ID

Pic 5. Custom URLDB content example



PEM can use flow information as a condition to apply an enforcement policy rule. There are various types of flow-specific properties that can be configured as a matching condition: DSCP Value, Protocol, IP Type, Source/Destination Address/Port, VLAN, etc. 

Pic 6. Flow condition rule example



Like any other BIG-IP module, PEM functionality can be extended and customized using iRules. Custom tab allows user to configure a specific condition not covered by built-in PEM functionality. As always, iRules are a powerful and flexible way to extend platform functionality. Please refer to DevCentral iRules API Wiki for PEM-specific iRules syntax. 


Enforcement policy rules are defined to perform a specific action within policy: limit bandwidth, close the “Gate” (block the traffic), redirect, insert HTML content, log messages etc. Some items may only be applicable to service providers - i.e. Application reporting and Rating Groups, therefore we will focus on configuration items that will be most commonly used by Education network admins.

  1. Reporting: usage, QoE, TCP Analytics
  2. Gate Status
  3. Forwarding
  4. Modify Header
  5. Insert Content
  6. QoS
  7. TCP Optimization
  8. Congestion Detection
  9. Custom Action (iRule)


Rather than describing each feature separately, let’s consider a few common use cases for these rules. For example, we can create 2 rules that block all traffic classified as “Phishing and other Frauds” by assigning a Gate Status “Disabled” and limit the bandwidth of Skype to 10Mbps max system-wide and 1Mbps max per user. The Classification rule will look similar to: 

Pic 7. Flow condition rule example

Bandwidth limiting rule uses Bandwidth controllers within QoS section:



The resulting Enforcement Policy will protect users from phishing and other fraudulent sites while limiting the bandwidth of Skype (including Video calls) to 1Mbps per user (and 10 Mbps total allocated for Skype application traffic). 
Flexible, user-aware classifications and a variety of traffic actions can be taken by individual rules to create the intelligent environment of flexible micro-granular control. This approach balances apps and services by both speed and priority, protects users (on-campus and remote students, staff, and visitors) from fraudulent and malicious activities and enhances overall quality of user experience by optimizing TCP and pacing video by preventing congestion on the ISP link. 


Institutions of any size can immediately start enjoying the incredible benefits that come with introduction of PEM Policies into their network. F5 engineers are available to make every project a success, helping customers from inception to a successful deployment. 

Next, we will dive into how PEM can save ISP link bandwidth by forcing streaming video to fallback to lower resolution while supporting the encrypted QUIC protocol. 


Stay tuned!

Published Apr 13, 2018
Version 1.0

Was this article helpful?