Cisco 7206 Network Configuration Guide - Page 90

Licensing Requirements for Layer 2 Port Modes Chapter 3 Configuring Layer 2 Interfaces Send document comments to [email protected] Licensing Requirements for Layer 2 Port Modes The following table shows the licensing requirements for this feature: Product Cisco NX-OS License Requirement Layer 2 port modes require no license. Any feature not included in a license package is bundled with the Cisco NX-OS system images and is provided at no extra charge to you. For a complete explanation of the Cisco NX-OS licensing scheme, see the Cisco NX-OS Licensing Guide. Note Using VDCs requires an Advanced Services license. Prerequisites for Layer 2 Interfaces Layer 2 interfaces have the following prerequisites: • You are logged onto the device. • You must configure the port as a Layer 2 port before you can use the switchport mode command. By default, all ports on the device are Layer 3 ports. Guidelines and Limitations VLAN trunking has the following configuration guidelines and limitations: • A port can be either a Layer 2 or a Layer 3 interface; it cannot be both simultaneously. • When you change a Layer 3 port to a Layer 2 port or a Layer 2 port to a Layer 3 port, all layer-dependent configuration is lost. When you change an access or trunk port to a Layer 3 port, all information about the access VLAN, native VLAN, allowed VLANs, and so forth, is lost. • Do not connect devices with access links because access links may partition a VLAN. • When connecting Cisco devices through an 802.1Q trunk, make sure that the native VLAN for an 802.1Q trunk is the same on both ends of the trunk link. If the native VLAN on one end of the trunk is different from the native VLAN on the other end, spanning tree loops might result. • Disabling spanning tree on the native VLAN of an 802.1Q trunk without disabling spanning tree on every VLAN in the network can cause spanning tree loops. You must leave spanning tree enabled on the native VLAN of an 802.1Q trunk. If you cannot leave spanning tree enabled, you must disable spanning tree on every VLAN in the network. Make sure that your network has no physical loops before you disable spanning tree. • When you connect two Cisco devices through 802.1Q trunks, the devices exchange spanning tree bridge protocol data units (BPDUs) on each VLAN allowed on the trunks. The BPDUs on the native VLAN of the trunk are sent untagged to the reserved IEEE 802.1D spanning tree multicast MAC address (01-80-C2-00-00-00). The BPDUs on all other VLANs on the trunk are sent tagged to the reserved Cisco Shared Spanning Tree (SSTP) multicast MAC address (01-00-0c-cc-cc-cd). Cisco Nexus 7000 Series NX-OS Interfaces Configuration Guide, Release 5.x 3-8 OL-23435-03