I am designing a network of about a hundred systems is different LANs . i would love to place an untangle linux box at the gateway which will serve as the dns , dhcp sever. My client said basically cisco standard network. with a cisco firewall enabled router do I still need the linux box? and I know cisco IOS is not a linux kernel
For your requirements it depends on the router model and more importantly the IOS version it has. For DHCP, I know most Cisco routers can act as DHCP servers. You'll probably not face any problem with that. For DNS, what I know is that some routers/IOS can only act as DNS proxy servers (forwarding for another dns main server) and/or authoritative DNS servers (for your own domains). However, they can NOT do DNS recursion. Recursion is the feature needed for querying the internet root servers and recursively resolving a domain name like say
why not trying to use both. If your company wants to have cisco equipments to standardize all of the network infrastructure that is great. it will ease troubleshooting since you only have Cisco products and will boost network performance and the management will be easier than having multiple vendors.
GIVE YOUR CLIENTS WHAT THEY WANT.
Would you forget about Linux? here where you have to convince them about untangle box, it would be so good to have a Linux box in your Network, it doesn't has to be on the Edge as a Gateway. you can deploy Linux as a bridge between your edge Cisco Router and your Internal Networks. you can show them the benefit of Untangle as a Spam Blocker, Web filtering, virus and Spywares blocker and a lot more.
they want to be connected to the Internet all the time and they probably have E-mails going back and forth, simple explain to them what Untangle could do and protect the Network in addition to your Cisco Infrastructure. in this way you will have both in your network and you will get the chance to deploy Untangle and gain experience having it in your network.