Barriers prevent access into servers by restricting entry, forcing Runners to involuntarily "end the run". To penetrate past barrier ice, Runners typically employ specialized icebreaker programs called fracters. Known barriers include:
Wall of Static is one of the most common barriers found protecting corporate servers. According to Ele "Smoke" Scovac: "There's nothing worse than seeing that beautiful blue ball of data just out of reach as your connection derezzes. I think they do it just to taunt us."
Paper Wall is a very cheap barrier that is destroyed the moment it is breached; it folds under pressure.
Bastion denies entry on all but a select few ports that might change with the time of day or picosecond of a connection. If you don't know what port to use, you're not getting in. Period.
Ice Wall is a Weyland-designed barrier that is the result of Liz Campbell, VP Project Security, asking Weyland R&D for "ice as impenetrable as a wall" - it's uncertain whether someone in R&D had a warped sense of humor or just a very literal mind.
Hadrian's Wall is a famous barrier constructed by Hadrian for Weyland Consortium. It is both hideously expensive for sysops to activate it and for Runners to break it.
The Jinteki-designed Himitsu-Bako is a simple ice barrier that appears as a digital puzzle box. What makes it special is the ease with which it can be uninstalled and installed in a different server, throwing up barriers in unexpected places and giving any intruder a curious feeling of deja vu.
The Jinteki Ashigaru, so named after the foot-soldiers of feudal Japan, becomes more fortified the denser the information cluster in corporate HQ. When it's fortified enough, the way past is to go a different way.
The NBN-designed TMI consists of a collection of cast-off cyberjunk - but it doesn't stay junk for long. "TMI" is probably a reference to "too much information".
Wraparound is an NBN barrier that, according to Noise, "...can make a real fine roller coaster, provided you’re properly stimmed up."
Haas-Bioroid has designed several bioroid ice that take on the form of guards that forbid entry into the server, thus functioning as barriers. Examples include Heimdall 1.0: "I hear the shift of every bit amid the flow of the datastream. I hear the whispers of my mothers, and their commands are law. The realm beyond is forbidden", Markus 1.0: "The forge must never run cold" and Eli 1.0: "That's against the rules. The Creators will be angry." However, it is possible for Runners to "talk" their way past them, as was done by Chaos Theory to Eli 1.0.