HP Cisco Catalyst Blade Switch 3020 Cisco Catalyst Blade Switch 3020 for HP So - Page 254
Encapsulation Types, IEEE 802.1Q Configuration Considerations, Function, Encapsulation
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Configuring VLAN Trunks Chapter 10 Configuring VLANs Table 10-4 Layer 2 Interface Modes Mode switchport mode access switchport mode dynamic auto switchport mode dynamic desirable switchport mode trunk switchport nonegotiate Function Puts the interface (access port) into permanent nontrunking mode and negotiates to convert the link into a nontrunk link. The interface becomes a nontrunk interface regardless of whether or not the neighboring interface is a trunk interface. Makes the interface able to convert the link to a trunk link. The interface becomes a trunk interface if the neighboring interface is set to trunk or desirable mode. The default switchport mode for all Ethernet interfaces is dynamic auto. Makes the interface actively attempt to convert the link to a trunk link. The interface becomes a trunk interface if the neighboring interface is set to trunk, desirable, or auto mode. Puts the interface into permanent trunking mode and negotiates to convert the neighboring link into a trunk link. The interface becomes a trunk interface even if the neighboring interface is not a trunk interface. Prevents the interface from generating DTP frames. You can use this command only when the interface switchport mode is access or trunk. You must manually configure the neighboring interface as a trunk interface to establish a trunk link. Encapsulation Types Table 10-5 lists the Ethernet trunk encapsulation types and keywords. Table 10-5 Ethernet Trunk Encapsulation Types Encapsulation Function switchport trunk encapsulation isl Specifies ISL encapsulation on the trunk link. switchport trunk encapsulation dot1q Specifies IEEE 802.1Q encapsulation on the trunk link. switchport trunk encapsulation negotiate Specifies that the interface negotiate with the neighboring interface to become an ISL (preferred) or IEEE 802.1Q trunk, depending on the configuration and capabilities of the neighboring interface. This is the default for the switch. The trunking mode, the trunk encapsulation type, and the hardware capabilities of the two connected interfaces decide whether a link becomes an ISL or IEEE 802.1Q trunk. IEEE 802.1Q Configuration Considerations The IEEE 802.1Q trunks impose these limitations on the trunking strategy for a network: • In a network of Cisco switches connected through IEEE 802.1Q trunks, the switches maintain one spanning-tree instance for each VLAN allowed on the trunks. Non-Cisco devices might support one spanning-tree instance for all VLANs. When you connect a Cisco switch to a non-Cisco device through an IEEE 802.1Q trunk, the Cisco switch combines the spanning-tree instance of the VLAN of the trunk with the spanning-tree instance of the non-Cisco IEEE 802.1Q switch. However, spanning-tree information for each VLAN is maintained by Cisco switches separated by a cloud of non-Cisco IEEE 802.1Q switches. The non-Cisco IEEE 802.1Q cloud separating the Cisco switches is treated as a single trunk link between the switches. 10-16 Cisco Catalyst Blade Switch 3020 for HP Software Configuration Guide OL-8915-01
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