VLANS, TRUNKS, AND VTP

  1. Use the vlan command to create your VLANs this can be done from Privilege EXEC mode within the vlan database or from Configuration mode. Use the switchport mode access command to define an interface as an access link and the switchport access vlan command to associate an interface to a VLAN.

  2. ISL encapsulates, whereas 802.1Q tags. ISL adds a 26-byte header and 4-byte trailer (CRC). 802.1Q inserts a 4-byte field and recomputes the frame's CRC. A native VLAN is a VLAN on an 802.1Q trunk where the frames for this VLAN are not tagged. This allows non-802.1Q devices also to be connected to the trunk.

  3. DTP is a Cisco-proprietary protocol to dynamically form trunks. One side needs to be set to trunk, dynamic desirable, or dynamic auto and the other to either trunk or dynamic desirable to form a trunk. Use nonegotiate to form trunks between a Cisco and non-Cisco switch. Use the switchport trunk encapsulation command to specify ISL or 802.1Q trunking. Use the switchport mode command to set the trunk. Use the switchport trunk vlan allowed command to restrict VLANs on a trunk.

  4. VTP server mode can create, modify, and delete VLANs, as well as advertise these changes. Clients can accept changes only from server switches. Transparent switches can also create, modify, and delete VLANs, but they don't advertise this and don't process messages from other switches.

  5. Use the vtp command to configure VTP: vlan database, vtp domain domain_name, vtp password password, vtp server|client|transparent, and vtp pruning. Use the show interface [switchport|trunk] command to troubleshoot pruning problems.



BCMSN Exam Cram 2 (Exam Cram 642-811)
CCNP BCMSN Exam Cram 2 (Exam Cram 642-811)
ISBN: 0789729911
EAN: 2147483647
Year: 2003
Pages: 171
Authors: Richard Deal

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