Layer 2 Lan Port Modes - Cisco WS-SUP32-GE-3B - Supervisor Engine 32 Software Configuration Manual

Understanding How Layer 2 Switching Works
Table 8-1
Encapsulation
switchport trunk encapsulation dot1q
switchport trunk encapsulation negotiate
The trunking mode, the trunk encapsulation type, and the hardware capabilities of the two connected
LAN ports determine whether a link becomes an ISL or 802.1Q trunk.

Layer 2 LAN Port Modes

Table 8-2
Table 8-2 Layer 2 LAN Port Modes
Mode
switchport mode access
switchport mode dynamic desirable
switchport mode dynamic auto
switchport mode trunk
switchport nonegotiate
DTP is a point-to-point protocol. However, some internetworking devices might forward DTP frames
Note
improperly. To avoid this problem, ensure that LAN ports connected to devices that do not support DTP
are configured with the access keyword if you do not intend to trunk across those links. To enable
trunking to a device that does not support DTP, use the nonegotiate keyword to cause the LAN port to
become a trunk but not generate DTP frames.
Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY
8-4
Ethernet Trunk Encapsulation Types (continued)
lists the Layer 2 LAN port modes and describes how they function on LAN ports.
Function
Puts the LAN port into permanent nontrunking mode and negotiates to convert the
link into a nontrunk link. The LAN port becomes a nontrunk port even if the
neighboring LAN port does not agree to the change.
Makes the LAN port actively attempt to convert the link to a trunk link. The LAN
port becomes a trunk port if the neighboring LAN port is set to trunk, desirable, or
auto mode. This is the default mode for all LAN ports.
Makes the LAN port willing to convert the link to a trunk link. The LAN port
becomes a trunk port if the neighboring LAN port is set to trunk or desirable mode.
Puts the LAN port into permanent trunking mode and negotiates to convert the link
into a trunk link. The LAN port becomes a trunk port even if the neighboring port
does not agree to the change.
Puts the LAN port into permanent trunking mode but prevents the port from
generating DTP frames. You must configure the neighboring port manually as a
trunk port to establish a trunk link.
Chapter 8 Configuring LAN Ports for Layer 2 Switching
Function
Specifies 802.1Q encapsulation on the trunk link.
Specifies that the LAN port negotiate with the
neighboring LAN port to become an ISL
(preferred) or 802.1Q trunk, depending on the
configuration and capabilities of the neighboring
LAN port.
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