Resolving a name through DNS does not mean a connection can be established. A subnet describes an address range, a VLAN divides a link-layer network logically, and a socket is an endpoint for communication. Check the name, address, port, and route separately to distinguish successful lookup from successful connection.
Key terms
DNS can map a name to an IP address. An address combined with a port can identify an endpoint for a transport protocol, but reachability and a listening service still need checking.
| Term | Meaning |
|---|---|
SYN | In the source terminology, the historical Synchronous Idle control character used in character-based communication. This is different from the SYN flag used to begin a TCP connection. |
SDN | Software-Defined Networking: an approach that separates network control from data forwarding and manages behavior through software-defined control. Implementations and benefits vary. |
QoS | Quality of Service: measures or mechanisms related to network performance, such as throughput, latency, loss, and prioritization. |
socket | A software endpoint for communication. For an Internet socket, the protocol, IP address, and port help identify where communication occurs. |
VLAN | Virtual Local Area Network: a logical separation of link-layer networks over physical network infrastructure. |
Terms to distinguish
| Term | Meaning |
|---|---|
Bit Padding | Adds bits to reach a required length or format. Bit stuffing instead inserts bits to prevent a reserved bit pattern from appearing in transmitted data. |
Multicast | Sends traffic to a selected group of receivers. |
Unicast | Sends traffic addressed to one receiver. |
Anycast | Several nodes advertise the same address, and routing delivers traffic to one of them according to routing policy. |
Subnet | A subdivision of an IP network defined by an address prefix. It identifies an address range; it is not necessarily one physical LAN segment. |
Terms in code
| Term | Meaning |
|---|---|
IPv6 | Internet Protocol version 6, using 128-bit addresses rather than IPv4's 32-bit addresses. Its address space is mathematically 2^96 times larger. |
Domain name | A human-readable name in the DNS hierarchy. Records can associate it with IP addresses and other information. |
DNS | Domain Name System: a hierarchical, distributed system for looking up records associated with domain names, including address records. |
Reading a technical document
A DNS answer gives an address, not proof that a socket is listening or that a network path permits the connection.
Start with the name and address, then examine the intended protocol and port. If a connection fails after lookup, the cause may be the route, a firewall rule, or the service rather than DNS.
Key takeaways
Separate names, addresses, network divisions, and communication endpoints.
- SYN — Here, the historical Synchronous Idle control character, not the TCP connection flag.
- Multicast — Delivers traffic to a selected receiver group.
- DNS — Looks up records in a distributed naming system; a successful lookup does not prove connectivity.
