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S7C4 – VLANs

S7C4 – VLANs. VLAN Details. Problems with Layer 2 Switching. Results in flat network structure Every device sees every pack transmitted Security All users have access to all devices Multiple paths to destinations Do not allow for redundant paths

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S7C4 – VLANs

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  1. S7C4 – VLANs VLAN Details

  2. Problems with Layer 2 Switching • Results in flat network structure • Every device sees every pack transmitted • Security • All users have access to all devices • Multiple paths to destinations • Do not allow for redundant paths • Are not capable of intelligent load balancing

  3. VLAN Characteristics • All VLAN members are in same broadcast domain • Logical subnet • Devices can exist any place in switch block • Membership usually based on port number • Can be dynamically assigned based on MAC • End-to-end throughout switch fabric • Can span several wiring closets or buildings

  4. VLANs Solve Problems • Efficient bandwidth utilization • Traffic routed between switches with router • Security • Forces layer 3 routing process to occur • Access lists • Load balancing • Layer 3 device determines best path • Isolation of problem components • Router keeps problems from propagating

  5. End-to-End VLAN • Users grouped into VLANs independent of physical location • All users have same 80/20 traffic flow pattern • As user moves, VLAN membership remains the same • Each VLAN has a common set of security requirements for all members

  6. Local VLANs • Range from single switch in a wiring closet to an entire building • Multiple paths to destinations • Maximum scalability by keeping the VLAN within a switch block

  7. VLAN Memberships • Static • Port-based – assigning a port to a VLAN • As device enters network, it assumes port’s VLAN • Requires administrator to make a port-to-VAN assignment for new connection when move is maDE • Dynamic • CiscoWorks 2000 or SWSI • As device enters network, it queries database for VLAN membership • Not covered in this course

  8. Configuring Static VLANs • Switch#vlan database • Switch(vlan)# vlan vl# name vlname • Switch (config)#int 1/1 • Switch (config-if)# switchport mode access • Switch (config-if)# switchport access vlan vl# • CLI • Set vlan vl# name vlname • Set vlan vl# mod#/portlist

  9. Verifying VLAN ConfigurationVLAN Identification • Show vlan • Displays each vlan number, status, and ports assigned • Identification • Frame Tagging • Places unique identifier in header of each frame • Called id or color • Used across backbone • Discarded if destination host is on same switch • VLAN hidden from end user

  10. Link Types • Access • Member of only one VLAN • Called port’s native VLAN • Can’t receive information from another VLAN • Requires router to communicate with another VLAN • Trunk • Fast Ethernet of Gigabit Ethernit (can be aggregated) • Can carry multiple VLANs • Cisco ISL or IEEE 802.1q • Does not belong to any specific VLAN • Does have a native VLAN – uses when trunk link fails

  11. ISL and 802.1q • ISL • Cisco proprietary • Can carry ethernet, tokenring, FDDI • Adds 26-byte header and 4-byte trailer to frame • 10-bit VLAN ID • 802.1q • Standardized • Embeds tagging information within frame • Adds 4-byte tag after source address field • First two bytes are 0x8100 (signifies 802.1Q tag) • Native VLAN not encapsulated with tagging information • SAID (security Association Identifier) – holds Cisco proprietary VLAN information

  12. NOTES • Dynamic Trunking Protocol – DTP • Can be manually configured for either ISL or 802.1q • Should be disables if switch has trunk line connected to router because router can’t participate in DTP negotiation protocol • Trunk Line Negotiations • Possible only if both switches belong to same VLAN Trunking Protocol management cdomain

  13. VLAN Trunk Configuration • (config)#int 1/3 • (config-if)#switchport mode trunk • (config-if)#switchport trunk encapsulation [isl | 802.1q] • (config-if)#switchport trunk allowed vlan remove vllist • (config-if)#switchport trunk allowed vlan add vllist • CLI Switch • Set trunk 3/1 [on|off |desirable|auto|nonegotiate] vlan—range [isl|dotq.1|lane|negotiate] • Dtp frames sent every 30 seconds • Clear trunk 3/1 vlan-range

  14. VTP Domains • Management Domains • Advertise attributes (revision number, known VLANs, VLAN parameters) • Server mode • Full control (default) • Client mode • Can’t create, change or delete VLANs • Transparent mode • Does not participate in VTP; does not advertise

  15. Advertisements • Management domain name • Configuration revision number • MD5 digest • Key sent with VTP when a password is assigned • Updater identity – switch sending advertisement

  16. VTP Configuration • VTP must be configured BEFORE VLAN • Switch#vlan database • Switch (vlan)# vtp domain domName • Switch (vlan)# vtp [server|client|transparent] • Switch (vlan)# password psswrd • Switch (vlan)# vtp v2-mode • CLI • Switch(enable) SET VTP DOMAIN DNAME [server|client|transparent] [password psswrd] • Switch (enable) set vtp v2 enable

  17. Confirming VTP • Show vtp domain • Shows version number, local mode, password • Show vtp counters • Shows exchange of advertisements • Show vtp statistics • Shows exchange of advertisements

  18. VTP Pruning • Disabled by default • Switch#vtp pruning • IOS • Set vtp pruning enable • Clear vtp pruneeligible vlan-range • Set vtp pruneligible vlan-range

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