[Glossary](https://telxpress.com/glossary/) / Network # Firewall A **firewall** is the security device or service that inspects traffic entering, leaving and crossing your network and allows or blocks it by rule, protecting your systems from the internet and from each other. - Network - Updated October 11, 2026 - Written by the Telxpress advisory team 01 In depth ## What it is, why it matters and *what to ask a vendor* Modern business firewalls, from vendors such as Fortinet, do more than block ports: they identify applications, filter web content, inspect for malware, terminate VPNs for remote staff, and enforce the rules between VLANs. NIST Special Publication 800-41 remains a plain guide to firewall policy and placement. For a growing business the firewall is where security policy becomes real: which systems the internet may reach, which staff may reach what from home, and which internal networks may talk to each other. It is also a performance point: an undersized or badly configured firewall adds latency to every call and meeting that crosses it. Ask who writes and reviews the rules and how often, whether the firewall is sized for your internet speed with inspection turned on, how remote access is secured (MFA on every VPN login), whether logs are kept and watched, how updates are applied, and what the support contract covers. Ask for the rule set to be documented in plain language you could hand to an auditor. 02 Related terms ## Terms that usually come up *alongside it* - Network ### [VLAN](https://telxpress.com/glossary/vlan/) A VLAN (virtual local area network) splits one physical network into separate logical networks, so that phones, computers, guest Wi-Fi, cameras and building systems are kept apart for security and performance without separate cabling. - Security & compliance ### [MFA (multi-factor authentication)](https://telxpress.com/glossary/mfa/) Multi-factor authentication (MFA) requires a second proof of identity beyond a password, such as a code from an app or a hardware key, and it defeats most attacks that rely on stolen passwords. - Connectivity ### [SD-WAN](https://telxpress.com/glossary/sd-wan/) SD-WAN (software-defined wide area network) is a service that combines two or more internet connections at a site, steers each application over the best path and fails over automatically when one connection degrades. - Security & compliance ### [Access control](https://telxpress.com/glossary/access-control/) Access control is the system of electronic locks, readers, credentials and management software that decides who may enter which door and when, and records every entry, replacing keys that cannot be revoked. 03 At Telxpress ## Where this shows up *at Telxpress* The pages and articles where this term does real work: what we advise, build and support. - Page ### [Business Networking, Firewalls & Managed Wi-Fi](https://telxpress.com/solutions/business-technology/networking/) Switching, routing, Fortinet firewalls, Ubiquiti and Cisco Meraki Wi-Fi and managed network services for offices that depend on reliable connections. - Article ### [Fortify Your Enterprise: Best Practices for a Secure Business Network](https://telxpress.com/insights/fortify-your-enterprise-best-practices-for-a-secure-business-network/) The layered network security practices that hold up in real offices, from patching and MFA to Wi-Fi hardening, tested backups and an incident plan, including the phone system. - Industry ### [AI & Business Technology for Financial Services](https://telxpress.com/industries/financial-services/) AI use cases for banks, advisors and lenders with GLBA, FINRA and SEC recordkeeping in mind, plus the systems we install and support. 04 Sources ## Public *references* The standard or law this definition rests on, as published by its owner. Fetched and checked on the review date above. - [NIST SP 800-41 Rev. 1, Guidelines on Firewalls and Firewall Policy](https://csrc.nist.gov/pubs/sp/800/41/r1/final) csrc.nist.gov Next step ## Want This Applied *to Your Business?* Book a free 30-minute AI readiness consultation. You'll leave with three AI opportunities specific to your business, whether you work with us or not. [Book My Free Consultation](https://telxpress.com/book/) [Take the Free AI Readiness Assessment](https://telxpress.com/ai-readiness/) [Or call 24/7: (949) 861-4500](tel:+19498614500) Last reviewed: October 11, 2026. Published by Telxpress, Irvine, CA.