I have always done some consulting, and most of the time enjoyed it a lot - and thus, I am looking forward to do a bit more.
firewalls and routers
Being one of the heads behind OpenBSD's packet filter, pf, and having started OpenBGPD, firewalls and routers are one of my main areas of interest. I never took a count, but have certainly setup dozens if not hundreds of firewalls, for medium-sized companies, large enterprises, authorities and ISPs. In many cases my job wasn't done with the setup, some customers outsourced the entire operations to my company. The same goes for routers. While the number is obviously much smaller - the scale of routers we talk here aren't all that common - the customers have been very well known entieties. As with the firewalls some customers have outsourced their entire router operations to us.
With the BSWS network as background I have helped many customers designing complex networks - by making them simpler, usually. My role in OpenBSD's network stack helps enormously in distinguishing relevant properties from marketing when selecting switches and other commercial networking gear, judging network protocol sanity and avoiding customer lock-ins, mostly by making sure open protocols are being used on all relevant interfaces between systems and devices. Switch configs are critical to network security and unfortunately most often forgotten. Hosting-ISP's networks for dedicated or customer's servers are one of the most vital environments in the world in that regard - I know what to do and what not to.
secure network programming
Having written many network-facing daemons, having privilege-seperated a lot of daemons in OpenBSD and outside, I have a lot of experience in this field that I want to share. If you write network-facing code I can help you making it robust and secure. This is best achieved in the design phase, adding security afterwards is often hard, sometimes indistinguishable from a rewrite. I can teach your staff to take robustness and security into account while designing and developing, I can help you with the design, and I can help you with the code. This area is very very dependent on the software and its environment in question, so please inquire for details.