Fluke 2680A User Manual page 252

2680A/2686A
Users Manual
•
A Bridge is used on Ethernet networks to isolate two portions of the network
at the Frame level (see Basic Network Packet and Frame Contents later in this
appendix). This is done to minimize transmission collisions, but the two
portions isolated by a Bridge remain on the same subnet. A Bridge also acts as
a Repeater.
•
A Router is used to isolate two portions of the network into subnets, as
described in IP Addresses and Segmented Networks in this appendix. A
Router also acts as a Bridge. Make sure your Router will route IP packets if
you want to place the PC and 2680 Series instruments in different subnets.
•
A Gateway is used to connect two networks with different architecture and
protocols. For example, a Gateway could be used to connect an Ethernet to an
X.25 net running on public telephone wiring. Gateways also perform Router,
Bridge, and Repeater functions.
The operation of 2680 Series software and instruments should be unaffected by a
properly designed network using any of these network devices. However, you
must use extra care when setting up PCs and 2680 Series instruments in a network
containing multiple subnets (net containing one or more routers and/or gateways).
The IP addresses assigned to the PC and instruments must be carefully selected in
this case. See IP Addresses and Segmented Networks for more information on IP
address assignment.
When a Bridge, Router, or Gateway is used in a network containing 2680 Series
instruments and hosts, be sure to reboot the host PC whenever an instrument is
moved from one section of the net to another. This is required to allow the network
hardware devices to initialize bridging and routing tables.
Also, when a 2680 Series instrument is used in a different subnet from the PC, the
Routers and Gateways used to connect the subnets must be able to route IP
packets. The default gateway addresses on the 2680 Series instrument and PC must
be set properly as well.
Basic Network Packet and Frame Contents
Network messages consist of short (mostly less than 1 KB) hunks of data,
surrounded by header and error detection information used by the protocols. The
message, together with the protocol information, is called a "Packet." When
physical network information (clock synchronization, error detection, etc.) is
wrapped around the packet, it is called a "Frame." The interface hardware adds and
strips off the Frame information around the packet. So, unless you're doing low-
level analysis of network traffic, you never need to deal with Frame information.
For any protocol, the Packet consists of a destination address, a source address,
some protocol type information, a message length field, and error detection
information.
H-4