[gmcenroe]

Thank you all for the numerous replies to this question. 

While I am still researching for the best solution, I am leaning toward setting up a VLAN from a managed switch. I looked at CISCO Catalyst 1000 which appears to be setup with easy management software rather than CLI, but it is only a level 2 switch. There are older CISCO switches that one can buy on ebay for far less that are level 3 for better security but they are end of life models and probably already heavily used, some require licenses, and I am not sure if they have the latest software installed or if I can update their firmware. Even the Catalyst 1000 8 port switch seems pretty expensive new from amazon ($289) or on ebay (similar price) for my use case. Other newer higher end models run over $1200, lol. There may be some other devices somewhere in between these 2 choices that are more affordable. I am still searching. 

There are also some good IRIX security white papers online that seem to enable hardening the system from attacks and run in a more secure mode that are quite helpful. 
See GIAC certification : Securing an IRIX 6.5.26 Workstation
Balancing Usability and Security in a Research Environment by Michael Schmit from September 2005

In the meantime I will just stay off the internet with my SGI.