So, some sort of 元 (IP) to L2 (MAC) address translation mechanism is required. Hence, the sending node needs to learn the receiving node's MAC address first. Thus, the task of sending an IP packet within an 元 segment boils down to sending an Ethernet frame with the IP packet inside to the L2 segment's node that owns that destination IP. IP protocol data units (packets) are encapsulated in the Ethernet protocol data units (frames). But how a node can reach another node (on the same 元 segment) by its IP address? How to send IP packetįirst and foremost, IP packets are sent wrapped into Ethernet frames (assuming the Layer 2 protocol in use is Ethernet, of course). Additionally, any node can emit a broadcast frame with the destination MAC ff:ff:ff:ff:ff:ff and it'll be delivered to all the nodes of its L2 segment. We know, that when a node emits a frame with a certain destination MAC address, it'll be delivered by the underlying L2 networking means to the destination node. Communication within a single L2 segment required only MAC (L2) addresses. Notice, that up to this point we haven't been talking about IP (元) addressing. VLANs split a single L2 segment (potentially formed by bridging multiple smaller L2 segments) into multiple non-intersecting L2 segments (and broadcast domains). Bridges merge multiple L2 segments (and broadcast domains) into one bigger L2 segment. VLAN technology can be seen as inverse to bridging. Hence, an L1 segment was forming a single collision domain (this is □).Ĭheck out the lab on how to set up a simple VLAN using a Linux bridge. Since multiple nodes could be transmitting frames simultaneously over a single cable, collisions were likely to occur. Thus, the nodes were forming a single broadcast domain (this is □). Everything sent by one of the nodes was seen by all other nodes of the segment. A coaxial cable served as a shared medium between multiple nodes. ![]() In the early days of the Ethernet, a bunch of computers connected to a shared coaxial cable was forming a physical segment (so-called bus topology). Nodes on a single L1 segment have a common physical layer. L1 segment ( aka physical segment, aka Ethernet segment) - a network segment formed by an electrical (or optical) connection between networked devices using a shared medium. The actual definition of a segment is technology-specific (see below). Network segment - a portion of a computer network. Examples: a bunch of computers connected to a network switch (Ethernet) a bunch of smartphones connected to a Wi-Fi access point (non-Ethernet). All the nodes of a single network link use the same link-layer protocol. Network link - a physical and logical network component used to interconnect nodes in the network. proximity) of the participants, not the 元 topology. The main determinant of a LAN is the locality (i.e. Much like any WAN, a LAN can consist of multiple IP networks communicating via routers. A LAN is not limited to a single IP subnetwork. LAN (Local Area Network) - a computer network that interconnects computers within a limited area such as a residence, school, office building, or data center. But I'll slightly touch upon its neighboring layers too. The primary focus will be on the Data link layer (OSI L2) of wired networks where the Ethernet is the king nowadays. ![]() This article is my layman's attempt to sort the basic things out with the minimum words and maximum drawings. The domain is pretty broad, and the terminology can get quite confusing quickly. ![]() As a software engineer, I need to deal with networking every now and then - be it configuring a SOHO network, setting up container networking, or troubleshooting connectivity between servers in a data center.
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