March 13th, 2009

Direct Routing Load Balancer. This is a software based load balancer, working at layer-4, for FreeBSD and NetBSD. Very similar to ipvs for linux. But drlb support only Direct Routing mode.

More information about direct routing.

We use it on a video platform that use several gigabytes of bandwidth. DRLB manage ten thousands of concurrents connections, without problem. But the path to a complete load-balancer is very long: currently, it doesn’t deal with ICMP, doesn’t send a TCP reset when it should. It doesn’t manage complex protocol like FTP.. But it works with IPv6, support four different load-balancing algorythms, and a maximum connection rate per server.

Further enhancements will be: *A total rewrite of lbdyn, with kqueue.

How it works ?

DRLB insert a hooks in pfil. It watch any incoming data. If an incoming connections is for a specified service (determined with IP and port) it will send it to one of the available servers. Servers can have a weight, in order to differenciate it’s capability. There are 4 schedulers available: round-robin, weighted-round-robin, least-connections and weighted-least-connections.

See the utilisation page.

Supported OS:

Version 0.9 have been tested from FreeBSD-6.3 to FreeBSD-7.0. The 1.0-alpha is not ready for freebsd. The version 1.0 is using MODULAR framework of NetBSD-current (5.99.7). lbdyn is not yet available for 1.0-alpha. The API for load-balancer configuration have been changed. So, I need to rewrite some code.

Download ?



License ?

DRLB is released under BSD license. See the LICENSE file in the archive for the copyright.

Why not continue IPVS for FreeBSD ?

First: no need to patch kernel. And because I want to learn kernel programming, because we have many problem with IPVS on linux, because we want only Direct Routing and a code that we can modify for our need… ! IPVS is not maintened anymore.


  • ports and pkgsrc
  • sharing of connections table not tested
  • lbdyn is not finished yet, with version 1.0.
  • icmp return and fragmentation
  • Many, many test.