Information Technology Reference
In-Depth Information
Before Calling Cisco Systems' TAC Team
Before calling Cisco Systems' Technical Assistance Center (TAC), make sure that you have read through
this chapter and completed the actions suggested for your system's problem.
Additionally, do the following and document the results so that we can better assist you:
•
Capture the output of
show version
from all the affected devices.
•
Capture the output of
show port mod_num/port_num
from all the affected ports.
•
Capture the output of
show port mod_num/port_num capabilities
from all the affected ports.
Additional Sources
•
IEEE web site: www.ieee.org/
ISL Trunking on Catalyst 5000 and 6000 Family Switches
This section illustrates how to create a switch-to-switch Inter-Switch Link (ISL) trunk. Trunk ports
enable connections between switches to carry traffic from more than one virtual local-area network
(VLAN). Without trunking, a link between two switches can carry only traffic from one VLAN.
•
This section shows how to determine the current behavior of a link. It goes on to show how users
can control the behavior, and it also explains situations when autonegotiation will fail.
•
Many different Cisco Catalyst switches and Cisco routers support autonegotiation. This section
focuses on autonegotiation between Catalyst 5000 switches. However, the concepts explained here
can be applied to the other types of devices.
Introduction
Trunking is not required in very simple switched networks with only one VLAN (broadcast domain). In
most LANs, a small portion of traffic is made up of special protocols used for managing the network
(Cisco Discovery Protocol, Virtual Trunking Protocol, Dynamic Trunking Protocol, Spanning-Tree
Protocol, and Port Aggregation Protocol, to name a few examples). The management VLAN (VLAN 1)
is also used when you
ping
or Telnet directly to or from the switch (this VLAN and the IP address of the
switch are defined by configuring the sc0 interface, explained later). In a multi-VLAN environment,
many network administrators advocate restricting this management traffic to its own VLAN, normally
VLAN 1. User traffic is then configured to flow in VLANs other than this default VLAN.
ISL (Cisco proprietary) is one of two possible trunking protocols for Ethernet. The other protocol is the
IEEE 802.1q standard.
Troubleshooting ISL Trunking on Catalyst 5000 and 6000 Family Switches
This section will walk the reader through some basic ISL trunking scenarios. The reader will learn basic
ISL trunking configuration and troubleshooting skills (Figure 23-4).
