System information

Chapter 2. Functional comparisons 9
2.1.1.3 Spanning tree protocol
The spanning tree protocol, part of the IEEE 802.1d specification, prevents
loops in a meshed network of Ethernet switches (or bridges).
Our interoperability tests verified that either the IBM switch or the Cisco
Catalyst switch could be the root bridge, and that either switch could be
forced to become the root bridge.
2.1.1.4 VLAN functions
IEEE 802.1Q port-based VLAN interoperated successfully. In Chapter 3,
“Ethernet switch interoperability” on page 25, we provide a detailed example
of how to configure a VLAN across an IBM 8275 and a Catalyst 2924. Make
sure that all the boxes where you plan to use IEEE 802.1Q really support it.
2.1.1.5 Traffic prioritization
IEEE 802.1p Specification is part of the IEEE 802.1D Standard, “Standard for
Local Area Network MAC Bridges”, and adds support for traffic priority to LAN
Make sure that the higher performance switch is the root switch in networks
with many switches.
Note
In small networks with few switches, the spanning tree protocol rarely gives
rise to difficulties. However, to install and operate larger Ethernet switch
networks successfully, it is of paramount importance that spanning tree
parameters are configured carefully, or extended network outages may
result. Do
not automatically assume there is an interoperability problem if
problems of network stability arise as Catalyst switches are added to a
network of IBM switches. It may well be a problem of configuring the
spanning tree protocol correctly.
Caution
On the switches we sampled, only VLAN 1 (the default VLAN) could
connect to the management functions of the switch. To ease configuration
management, we suggest that you leave one port on each switch in VLAN
1, and that VLAN 1 is not excluded from travelling across trunks. However,
be cautious of the security exposure if servers or clients are inadvertently
connected to a VLAN 1 port.
Tip