Trunking Support - Cisco WS-C2948G-GE-TX Configuration Manual

Chapter 11 Configuring VLAN Trunks on Fast Ethernet and Gigabit Ethernet Ports
The trunking mode, the trunk encapsulation type, and the hardware capabilities of the two connected
ports determine whether a trunk link comes up and the type of trunk the link becomes.
the result of the possible trunking configurations.
Table 11-3 Results of Possible Fast Ethernet and Gigabit Ethernet Trunk Configurations
Neighbor Port
Trunk Mode and
Trunk
Encapsulation
off
dot1q
on
dot1q
desirable
dot1q
auto
dot1q
DTP is a point-to-point protocol. However, some internetworking devices might forward DTP frames
Note
improperly. To avoid this problem, ensure that trunking is turned off on ports that are connected to
nonswitch devices if you do not intend to trunk across those links. When manually enabling trunking on
a link to a Cisco router, use the nonegotiate keyword to cause the port to become a trunk but not generate
DTP frames.

Trunking Support

Trunking capabilities are hardware dependent.
hardware that supports the two trunking encapsulations. To determine whether a specific piece of
hardware supports trunking, and to determine which trunking encapsulations are supported, see your
hardware documentation or use the show port capabilities command.
Catalyst 4500 Series, Catalyst 2948G, Catalyst 2948G-GE-TX, and Catalyst 2980G Switches Software Configuration Guide—Release 8.2GLX
78-15908-01
Local Port Trunk Mode and Trunk Encapsulation
off on
dot1q dot1q
Local: Local:
Nontrunk 1Q trunk
Neighbor: Neighbor:
Nontrunk Nontrunk
Local: Local:
Nontrunk 1Q trunk
Neighbor: Neighbor:
1Q trunk 1Q trunk
Local: Local:
Nontrunk 1Q trunk
Neighbor: Neighbor:
Nontrunk 1Q trunk
Local: Local:
Nontrunk 1Q trunk
Neighbor: Neighbor:
Nontrunk 1Q trunk
Understanding How VLAN Trunks Work
desirable
dot1q
Local:
Nontrunk
Neighbor:
Nontrunk
Local:
1Q trunk
Neighbor:
1Q trunk
Local:
1Q trunk
Neighbor:
1Q trunk
Local:
1Q trunk
Neighbor:
1Q trunk
Table 11-4 shows which switches have available
Table 11-3 shows
auto
dot1q
Local:
Nontrunk
Neighbor:
Nontrunk
Local:
1Q trunk
Neighbor:
1Q trunk
Local:
1Q trunk
Neighbor:
1Q trunk
Local:
Nontrunk
Neighbor:
Nontrunk
11-3