What is BNG? Broadband Network Gateway (BNG) allows for a centralized access point for subscribers to which they connect to the internet. BNG establishes and manages subscriber sessions in this centralized access point for easy management and scalability. When a session is active, BNG aggregates the traffic from various subscriber points on an access network and routes it to the network of the service provider.
We’re seeing ISPs of all sizes go to this type of model to help ease the challenges of managing a customer base and all the network equipment that goes into it.
One of the main goals with BNG is to move all customer-facing logical interfaces to one or two points on the network. In most designs, QinQ (IEEE 802.1Q) is used to bring the customer's data back to the BNG router (but there are other options). For example, on a per chassis basis you would assign a VLAN per subscriber with an outer tag assigned to that chassis. The customer speeds and other settings are all managed in one or two centralized RADIUS servers, making a single place to make a customer change.
How can BNG help avoid an IPv4 address acquisition? One of the biggest issues challenging all ISPs right now is the IPv4 exhaustion problem. Unlike traditional ISP services where it is necessary to split up customer's subnets, with BNG, all customers can be put on a single broadcast domain and a single DHCP pool because BNG does not allow customers to broadcast outside of their own virtual interface. This prevents wasting IP addresses by not having to split them up and having a dangerously large broadcast domain.
The other way to alleviate the IPv4 exhaustion is to dual-stack IPv6 and CGNAT IPv4. Because everything in BNG is centralized, it makes it very easy to apply IPv6 to a single customer or all customers without having to redesign the entire network to get IPv6 to the edge. CGNAT can then also be applied with an appliance sitting between the outgoing interface of the BNG and the internet creating a "catch-all" for customers that need NAT added to their connection. The dual-stack option allows approximately 80% of the traffic destined for the internet to use IPv6 and the other 20% needing to be NAT'd. Many of our 7Sigma customers with this design have been able to lower the hardware and licensing requirements on their CGNAT box, saving money in that area and keeping the majority of traffic off of NAT giving customers a better user experience.
How does BNG work? One of the ways this works is by “dumbing down” the access gear to make each chassis more like a fiber switch (or DSL switch), which allows the ability to have a single template to use over and over on the network for each chassis. In the event of a failure or bringing up a new site, there is really only the name, IP and outer VLAN that need to be changed to get things online. Chassis’ can be pre-configured, freeing up higher-end resources from having to spend so much time configuring and installing.
All the customer speeds would be located as a policer and shaper on the BNG router. The RADIUS server then holds the package that each customer is on that corresponds to the policer and shaper on the router. To do a mass upgrade of customers (ie. upgrade all customers on 10Mb to 20Mb), only an update to the speeds associated with the BNG router is required along with a one-line mass database update in RADIUS. The process is the same to upgrade 10 customers or 1,000 customers, which means it only takes a few minutes to upgrade thousands of customers.
These examples demonstrate the scalability of the network. Deploying BNG can greatly improve all the difficulties that come with scaling on your network. It also allows a smaller staff the ability to manage a much larger network, without needing to add staff for every nth customer added as a subscriber.
Is BNG right for you? If you’re struggling to scale, or managing a network with a reduced staff, BNG may be a good approach. Want to talk through your options? Give us a call or send us an email any time.