{{short description|Software or hardware-based network security system}}
In [[computing]], a '''firewall''' is a [[network security]] system that [[Network monitoring|monitors]] and controls incoming and outgoing [[network traffic]] based on predeterminedconfigurable security rules.<ref>{{cite book | first1=Noureddine | last1=Boudriga | title=Security of mobile communications | url=https://archive.org/details/securitymobileco00boud | url-access=limited | publisher=CRC Press | date=2010 | ___location=Boca Raton | pages=[https://archive.org/details/securitymobileco00boud/page/n66 32]–33 | isbn=978-0849379420}}</ref><ref>{{Cite journal |last1=Macfarlane |first1=Richard |last2=Buchanan |first2=William |last3=Ekonomou |first3=Elias |last4=Uthmani |first4=Omair |last5=Fan |first5=Lu |last6=Lo |first6=Owen |date=2012 |title=Formal security policy implementations in network firewalls |url=https://linkinghub.elsevier.com/retrieve/pii/S0167404811001192 |journal=Computers & Security |language=en |volume=31 |issue=2 |pages=253–270 |doi=10.1016/j.cose.2011.10.003}}</ref> A firewall typically establishes a barrier between a trusted network and an untrusted network, such as the [[Internet]].,<ref name="Oppliger 1997 94">{{cite journal|last=Oppliger|first=Rolf|title=Internet Security: FIREWALLS and BEYOND|journal=Communications of the ACM|date=May 1997|volume=40|issue=5|page=94|doi=10.1145/253769.253802|s2cid=15271915|doi-access=free}}</ref> or between several [[VLAN]]<nowiki/>s.
