Extreme Networks ExtremeWare XOS Command Reference Manual page 556

ExtremeWare XOS 11.5 supports only the Summit X450 family of switches and the BlackDiamond 8800 series switch.
Commands for Status Monitoring and Statistics
Extreme Link Status Monitoring
ExtremeWare XOS 11.4 introduces support for the Extreme Link Status Monitoring (ELSM) protocol.
ELSM is an Extreme Networks proprietary protocol that monitors network health by detecting CPU and
remote link failures. ELSM is available only on Extreme Networks devices and operates on a point-to-
point basis. You configure ELSM on the ports that connect to other network devices and on both sides
of the peer connection.
ELSM monitors network health by exchanging various hello messages between two ELSM peers. ELSM
uses an open-ended protocol, which means that an ELSM-enabled port expects to send and receive hello
messages from its peer. The Layer 2 connection between ports determines the peer connection. Peers can
be either directly connected or separated by one or more hubs. If there is a direct connection between
peers, they are considered neighbors.
If ELSM detects a a failure, the ELSM-enabled port responds by blocking traffic on that port. For
example, if a peer stops receiving messages from its peer, ELSM brings down that connection. ELSM
does this by blocking all incoming and outgoing data traffic on the port and notifying applications that
the link is down.
In some situations, a software or hardware fault may prevent the CPU from transmitting or receiving
packets, thereby leading to the sudden failure of the CPU. If the CPU is unable to process or send
packets, ELSM isolates the connections to the faulty switch from the rest of the network. If the switch
fabric sends packets during a CPU failure, the switch may appear healthy when it is not. For example, if
hardware forwarding is active and software forwarding experiences a failure, traffic forwarding may
continue. Such failures can trigger control protocols such as Extreme Standby Router Protocol (ESRP) or
Ethernet Automatic Protection Switching (EAPS) to select different devices to resume forwarding. This
recovery action, combined with the CPU failure, can lead to loops in a Layer 2 network.
Configuring ELSM on Extreme Networks devices running ExtremeWare XOS is backward compatible
with Extreme Networks devices running ExtremeWare.
sFlow Statistics
®
sFlow is a technology for monitoring traffic in data networks containing switches and routers. It relies
on statistical sampling of packets from high-speed networks, plus periodic gathering of the statistics. A
User Datagram Protocol (UDP) datagram format is defined to send the information to an external entity
for analysis. sFlow consists of a (Management Information Base) MIB and a specification of the packet
format for forwarding information to a remote agent. Details of sFlow specifications can be found in
RFC 3176 and at the following website:
http://www.sflow.org
ExtremeWare XOS allows you to collect sFlow statistics on a per port basis. An agent, residing locally
on the switch, sends data to a collector that resides on another machine. You configure the local agent,
the address of the remote collector, and the ports of interest for sFlow statistics gathering. You can also
modify default values for how frequently on average a sample is taken, how often the data is sent to the
collector, and the maximum load allowed on the CPU before throttling the statistics gathering.
556
ExtremeWare XOS 11.5 Command Reference Guide