Information Technology Reference
In-Depth Information
EtherChannel
EtherChannel
is a technique that can be used when you have multiple connections to the same device.
Instead of having each link function independently, EtherChannel groups the ports together to work as
one unit. It distributes traffic across all the links and provides redundancy in case one or more links fail.
EtherChannel settings must be the same on both sides of the links involved in the channel. Normally, the
Spanning-Tree Protocol would block all these parallel connections between devices because they are
loops; however, EtherChannel runs “underneath” Spanning-Tree Protocol so that the protocol thinks that
all the ports within a given EtherChannel are only a single port.
Multilayer Switching
Multilayer switching
(MLS) refers to the capability of a switch to forward frames based on information
in the Layer 3 (and sometimes Layer 4) header. This usually applies to IP packets, but now it also can
occur for IPX packets. The switch learns how to handle these packets by communicating with one or
more routers. Using a simplified explanation, the switch watches how the router processes a packet, and
then the switch takes over processing future packets in this same flow. Traditionally, switches have been
much faster at switching frames than routers, so to have them offload traffic from the router can result
in significant speed improvements. If something changes in the network, the router can tell the switch to
erase its Layer 3 cache and build it from scratch again as the situation evolves. The protocol used to
communicate with the routers is called Multilayer Switching Protocol (MLSP).
How to Learn About These Features
These are just some of the basic features that switches support. More are being added every day. It is
important to understand how your switches work, which features you are using, and how those features
should work. One of the best places to learn this information about Cisco switches is on Cisco's web site.
Go to www.cisco.com; under the section “Service & Support,” select Technical Documents. From here,
select Documentation Home Page to find documentation sets for all Cisco products. The “Multilayer
LAN Switches” link will lead you to documentation for all Cisco LAN switches. To learn about the
features of a switch, read the “Software Configuration Guide” for the particular release of software that
you use. The software configuration guides give you background information about what the feature
does and what commands to use to configure it on your switch. All this information is free on the web;
you do not even need an account for this documentation because it is available to anyone. Some of these
configuration guides can be read in an afternoon and are well worth the time spent.
Another part of Cisco's web site is populated by Cisco's Technical Assistance Center (TAC). It is filled
with information designed to help you implement, maintain, and troubleshoot your network. Go to the
TAC web site at: www.cisco.com/tac; from here, you can select Products Home Page to get detailed
support information organized by specific products, or you can go to the Technologies Home Page to get
support information on technology (Fast Ethernet, Spanning-Tree Protocol, trunking, and so on). TAC
documents and online tools specific to LAN Technologies are here:
www.cisco.com/warp/customer/473/. Some of the material on the TAC web site, and, in particular, the
online tools, are accessible only to users with a Cisco support contract.
