Page 1 Switching Technologies Lecture 4C Hassan Shuja 03/28/2006

Page 2 Switching Technologies Trunking – A method to support multiple VLANs that have members on more than one switch – Switches tag each frame so that the receiving switch knows which VLAN the frame belongs to – Two trunking methods – Cisco Inter-Switch Link (ISL) – IEEE 802.1q – Cisco ISL – ISL created before IEEE standardized a trunking protocol – ISL is a Cisco proprietary so it can only be used between Cisco switches – ISL encapsulates each Ethernet frame with an ISL header and trailer – ISL header is 26 bytes – VLAN number is encoded in header – ISL trailer is 4 bytes CRC

Page 3 Switching Technologies Trunking – 802.1q – Developed in 1998 – Actual frame is modified or tagged – 4 bytes are added to the original Ethernet header – A field within this header identifies the VLAN number

Page 4 Switching Technologies Dynamic Trunk Protocol (DTP) – DTP is the process that takes place to determine whether tow connecting devices can create a trunk connection – Supports auto-negotiations for both ISL and 802.1q

Page 5 Switching Technologies VLAN Trunking Protocol (VTP) – VTP is a Cisco proprietary messaging protocol that occurs between devices on trunk ports – Allows VLAN information to be propagated across your switched network so you have a consistent VLAN configuration – Makes management easy – Propagates across mixed media – VTP configuration – VTP Domain – A management domain is a grouping of switches that will be sharing information about VLANs – VTP Modes – Server – Responsible for making all VLAN configurations (adds/changes/deletions) – Client – Accepts VTP messages – Transparent – Do not participate in management domain but do forward messages

Page 6 Switching Technologies VLAN Trunking Protocol (VTP) – VTP Messages – Summary – Generated every 300 seconds to ensure all switches are in sync – Contains a revision number – Request – Generated to acquire VLAN information – Subset – Generated in response to a request – VTP Pruning – Allows a switch to make intelligent decisions concerning the forwarding of multicast, broadcast, and unknown destinations across trunk ports – Turned off by default – Switch must be in Server mode – Pruning can be done manually

Page 7 Switching Technologies VTP Configuration