S
SA
Source address. The SA is the IP or MAC address of the device issuing the
packet.
SCP
Secure Copy Protocol. SCP2, part of SSH2, is used to transfer configuration and policy
files.
SDN
Software-defined Networking. An approach to computer networking that seeks to manage
network services through decoupling the system that makes decisions about where traffic is
sent (control plane) from the underlying systems that forward traffic to the selected
destination (data plan).
secondary port
In
EAPS, the secondary port is a port on the master node that is
designated the secondary port to the ring. The transit node ignores the secondary port
distinction as long as the node is configured as a transit node.
segment
In Ethernet networks, a section of a network that is bounded by bridges, routers, or
switches. Dividing a LAN segment into multiple smaller segments is one of the most common ways
of increasing available bandwidth on the LAN.
server
certificate
A certificate
identifying a server. When a client connects to the server, the server sends its certificate
to the client and the client validates the certificate to trust the server.
sFlow
sFlow allows you to monitor network traffic by statistically sampling the network
packets and periodically gathering the statistics. The sFlow monitoring system consists of an
sFlow agent (embedded in a switch, router, or stand-alone probe) and an external central data
collector, or sFlow analyzer.
SFP
Small form-factor pluggable. These transceivers offer high speed and physical
compactness.
slow path
This term refers to the data path for packets that must be processed by the switch
CPU, whether these packets are generated by the CPU, removed from the network by the CPU, or
simply forwarded by the CPU.
SLP
Service Location
Protocol. A method of organizing and locating the resources (such as printers, disk drives,
databases, e-mail directories, and schedulers) in a network.
Using SLP, networking
applications can discover the existence, location and configuration of networked devices.
With Service Location Protocol, client applications are 'User Agents' and services are
advertised by 'Service Agents'. The User Agent issues a multicast 'Service Request'
(SrvRqst) on behalf of the client application, specifying the services required. The User
Agent will receive a Service Reply (SrvRply) specifying the location of all services in the
network which satisfy the request.
For larger networks, a third entity, called a 'Directory
Agent', receives registrations from all available Service Agents. A User Agent sends a
unicast request for services to a Directory Agent (if there is one) rather than to a Service
Agent.
(SLP version 2, RFC2608, updating RFC2165)
SMF
Single-mode fiber. SMF
is a laser-driven optical fiber with a core diameter small enough to limit transmission to a
single bound mode. SMF is commonly used in long distance transmission of more than three
miles; it sends one transmission at a time.
SMI
Structure of Management
Information. A hierarchical tree structure for information that underlies Management
Information Bases (MIBs), and is used by the SNMP protocol. Defined in RFC 1155 and RFC 1442
(SNMPv2).
SMON
Switch Network Monitoring Management (MIB) system defined by the IETF document RFC
2613. SMON is a set of MIB extensions for RMON that allows monitoring of switching equipment
from a SNMP Manager in greater detail.
SMT
Station Management. The
object class in the 802.11 MIB that provides the necessary support at the station to manage
the processes in the station such that the station may work cooperatively as a part of an IEEE
802.11 network. The four branches of the 802.11 MIB are:
- dot11smt—objects
related to station management and local configuration
- dot11mac—objects
that report/configure on the status of various MAC parameters
- dot11res—objects
that describe available resources
- dot11phy—objects
that report on various physical items
SNMP
Simple Network Management Protocol. SNMP is a standard that uses a common software
agent to remotely monitor and set network configuration and runtime parameters. SNMP operates
in a multivendor environment, and the agent uses MIBs, which define what information is
available from any manageable network device. You can also set traps using SNMP, which send
notifications of network events to the system log.
SNTP
Simple Network Time Protocol. SNTP is used to synchronize the system clocks throughout
the network. An extension of the Network Time Protocol, SNTP can usually operate with a single
server and allows for IPv6 addressing.
SSH
Secure Shell, sometimes known as Secure Socket Shell, is a UNIX-based command
interface and protocol of securely gaining access to a remote computer. With SSH commands,
both ends of the client/server connection are authenticated using a digital certificate, and
passwords are protected by being encrypted. At Extreme Networks, the SSH is a separate
software module, which must be downloaded separately. (SSH is bundled with SSL in the software
module.)
SSID
Service Set Identifier.
A 32-character unique identifier attached to the header of packets sent over a Wireless LAN
that acts as a password when a wireless device tries to connect to the Basic Service Set
(
BSSs). Several BSSs can be
joined together to form one logical WLAN segment, referred to as an extended service set
(
ESS). The SSID is used to
identify the ESS.
In 802.11 networks, each access
point (AP) advertises its presence several times per second by broadcasting beacon frames
that carry the ESS name (SSID). Stations discover APs by listening for beacons, or by
sending probe frames to search for an AP with a desired SSID. When the station locates an
appropriately-named access point, it sends an associate request frame containing the desired
SSID. The AP replies with an associate response frame, also containing the SSID.
Some APs
can be configured to send a zero-length broadcast SSID in beacon frames instead of sending
their actual SSID. The AP must return its actual SSID in the probe response.
SSL
Secure Sockets Layer.
SSL is a protocol for transmitting private documents using the Internet. SSL works by using a
public key to encrypt data that is transferred over the SSL connection. SSL uses the
public-and-private key encryption system, which includes the use of a digital certificate. SSL
is used for other applications than SSH, for example, OpenFlow.
spoofing
Hijacking a server‘s IP address or hostname so that requests to the server are
redirected to another server. Certificate validation is used to detect and prevent
this.
standard mode
Use ESRP standard mode if your network contains switches running ExtremeWare and
switches running ExtremeXOS, both participating in ESRP.
STP
Spanning Tree Protocol. STP is a protocol, defined in IEEE 802.1d, used to eliminate
redundant data paths and to increase network efficiency. STP allows a network to have a
topology that contains physical loops; it operates in bridges and switches. STP opens certain
paths to create a tree topology, thereby preventing packets from looping endlessly on the
network. To establish path redundancy, STP creates a tree that spans all of the switches in an
extended network, forcing redundant paths into a standby, or blocked, state. STP allows only
one active path at a time between any two network devices (this prevents the loops) but
establishes the redundant links as a backup if the initial link should fail. If STP costs
change, or if one network segment in the STP becomes unreachable, the spanning tree algorithm
reconfigures the STP topology and re-establishes the link by activating the standby
path.
STPD
Spanning Tree Domain. An STPD is an STP instance that contains one or more VLANs. The
switch can run multiple STPDs, and each STPD has its own root bridge and active path. In the
Extreme Networks implementation of STPD, each domain has a carrier VLAN (for carrying STP
information) and one or more protected VLANs (for carrying the data).
STPD mode
The mode of operation for the STPD. The two modes of operation are:
- 802.1d—Compatible with legacy STP and other devices using the IEEE 802.1d standard.
- 802.1w—Compatible with Rapid Spanning Tree (RSTP).
stub areas
In
OSPF, a stub area is connected to only one other area (which can
be the backbone area). External route information is not distributed to stub areas.
subnets
Portions of networks that share the same common address format. A subnet in a TCP/IP
network uses the same first three sets of numbers (such as 198.63.45.xxx), leaving the fourth
set to identify devices on the subnet. A subnet can be used to increase the bandwidth on the
network by breaking the network up into segments.
superloop
In
EAPS, a superloop occurs if the common link between two EAPS
domains goes down and the master nodes of both domains enter the failed state putting their
respective secondary ports into the forwarding state. If there is a data VLAN spanning both
EAPS domains, this action forms a loop between the EAPS domains.
SVP
SpectraLink Voice
Protocol, a protocol developed by SpectraLink to be implemented on access points to facilitate
voice prioritization over an 802.11 wireless LAN that will carry voice packets from
SpectraLink wireless telephones.
syslog
A protocol used for the
transmission of
event notification
messages across networks, originally developed on the University of California Berkeley
Software Distribution (BSD) TCP/IP system implementations, and now embedded in many other
operating systems and networked devices. A device generates a messages, a relay receives and
forwards the messages, and a collector (a syslog server) receives the messages without
relaying them.
Syslog uses the user datagram protocol (UDP) as its underlying transport layer
mechanism. The UDP port that has been assigned to syslog is 514. (RFC 3164)
system health check
The primary responsibility of the system health checker is to monitor and poll error
registers. In addition, the system health checker can be enabled to periodically send
diagnostic packets. System health check errors are reported to the syslog.