Network Glossary
ISP technical terms explained in plain language — from engineers who operate provider networks daily.
AS — Autonomous System
A group of IP networks under a single administration, identified by an ASN. Every ISP needs at least one AS to advertise its routes via BGP.
Anycast — Anycast Routing
Multiple servers share the same IP from different locations; the network delivers each packet to the closest one. Common in DNS (8.8.8.8, 1.1.1.1) and CDNs.
BFD — Bidirectional Forwarding Detection
Protocol that detects link failures in milliseconds. Used alongside BGP, OSPF and MPLS for fast convergence. Essential in networks with tight SLA requirements.
BGP — Border Gateway Protocol
The routing protocol between Autonomous Systems — what makes the internet work between ISPs. Misconfigured BGP can take you off the internet or leak someone else's routes.
BNG — Broadband Network Gateway
Evolution of the B-RAS. Combines subscriber session termination (PPPoE, IPoE), QoS policy enforcement, CGNAT and traffic forwarding in a single control point.
B-RAS — Broadband Remote Access Server
Server that terminates subscriber PPPoE sessions and routes traffic. Huawei NE8000/NE40, Juniper MX, Cisco ASR. Single point of failure without redundancy.
CGNAT — Carrier-Grade NAT
Large-scale NAT that lets you share one public IPv4 across many subscribers. Cheaper than buying IPv4, but breaks some services (P2P, port forwarding, gaming).
DNS — Domain Name System
Translates names (rasys.net) into IPs (200.x.x.x). ISPs need to run their own resolvers or point to public ones. Slow DNS is the first thing customers complain about.
ECMP — Equal-Cost Multi-Path
Distributes traffic across multiple equal-cost paths. Common in OSPF and BGP to load-balance across uplinks without additional protocols. Requires consistent per-flow hashing.
GPON — Gigabit Passive Optical Network
Passive FTTH technology (no power in the path). One OLT serves up to 128 ONUs per port via optical splitter. Dominant standard for residential fiber in Brazilian ISPs.
HSRP — Hot Standby Router Protocol
Cisco proprietary gateway redundancy protocol. One active router, one standby; automatic failover. Equivalent to VRRP (open standard) and GLBP (with load balancing).
IPv6 — Internet Protocol version 6
Next-generation IP with 128-bit addresses. Solves IPv4 scarcity. ISPs without IPv6 tend to depend more on CGNAT and may see worse experience on modern services, CDNs, and latency-sensitive applications.
IX — Internet Exchange Point
Location where ISPs interconnect directly without paying for IP transit. In Brazil, IX.br has PoPs in major cities. Peering at IX cuts latency and cost.
LACP — Link Aggregation Control Protocol
802.3ad protocol that bundles multiple physical links into a single logical channel. Increases bandwidth and adds redundancy. Essential on server uplinks and core switch interconnects.
MPLS — Multiprotocol Label Switching
Switches packets based on labels instead of IP destination. Used in large backbones to build L2/L3 VPNs and perform traffic engineering. Common in multi-PoP ISPs.
MSS — Maximum Segment Size
Maximum TCP segment size without fragmentation. Must be adjusted when CGNAT, tunneling or PPPoE is in play (MTU below 1500). Wrong MSS silently breaks HTTPS connections.
MTU — Maximum Transmission Unit
Maximum packet size on a given link. Standard Ethernet: 1500 bytes. PPPoE drops it to 1492. MPLS and tunnels reduce it further. Incorrect MTU causes intermittent connection drops.
OLT — Optical Line Terminal
Central device of a GPON/EPON FTTH network. Connects the ISP backbone to the ONUs (subscriber side). Huawei MA5800, ZTE C300, FiberHome AN5516 are common.
OSPF — Open Shortest Path First
Interior gateway protocol based on link-state. Calculates shortest paths inside the ISP's AS. Faster than RIP, simpler than IS-IS.
Peering — BGP Peering
Direct route exchange between two ASes without paying transit. Can be bilateral (direct agreement) or multilateral (via IX). Cuts bandwidth cost and improves latency.
PPPoE — Point-to-Point Protocol over Ethernet
Authentication protocol still dominant in Brazilian ISPs. Client authenticates via login/password over a PPP session encapsulated in Ethernet. The B-RAS terminates the session.
QinQ — IEEE 802.1ad (Double VLAN)
Encapsulates a VLAN inside another VLAN (S-TAG + C-TAG). Isolates customer traffic on metro Ethernet without exhausting the VLAN space (4096 IDs). Used in ISP backbones.
RADIUS — Remote Authentication Dial-In User Service
Central authentication, authorization and accounting (AAA) system that validates PPPoE login, enforces contracted speed and tracks online time. FreeRADIUS is the most common base.
RPKI — Resource Public Key Infrastructure
BGP route certification system. Validates that whoever announces a prefix has authorization from the IP block owner. Reduces risk of route hijacking and BGP leaks.
VRRP — Virtual Router Redundancy Protocol
Open standard (RFC 5798) for gateway redundancy. A virtual router shares IP and MAC between devices; the active master handles traffic, the backup takes over on failure. Open alternative to HSRP.
Want to dig deeper?
Rasys has been operating ISP networks in Brazil for over 6 years. If any of these terms is a headache in your operation, talk to us — initial conversation, no commitment.