Unit 8. Spanning Tree protocol, Virtual LANs (VLANs) and Access Networks

Transcription

1 nit 8 panning ree protocol, Virtual s (Vs) and ccess etworks

2 panning ree Protocol (P) Designed to prevent bridging loops ach bridge has unique D consisting of Priority + address n power up the bridge or layer switch send out BPD (Bridge Protocol Data nit) to determine the spanning tree topology Bridge states Blocking default power on state istening listens for BPDs to avoid loops earning Builds address table Forwarding sends and received all data on bridged port sually takes 50 seconds to reach convergence Root Bridge he bridge having the lowest identifier is chosen to be the root of the spanning tree.

3 Bridge Port onfiguration Root bridge is determined by having the Bridge D and path cost (lowest always wins) Priority ost ddress Root bridge all ports forwarding on-root bridges Root port forwarding Designated port forwarding ll other ports blocking ccess Ports - forwarding

4 Priority he bridge D = Priority + ddress Priority = (isco uses increments of 4096) he root bridge is identified as the bridge with the lowest BD. When there is a tie for the least cost path, the tie is broken by using the priority. an you see why this can create a problem?

5 osts P calculates the path cost based on the media speed (bandwidth) Root port - the port with the lowest path cost to the root bridge becomes the root port. f the speed/duplex of the port is changed, spanning tree recalculates the path cost automatically. change in the path cost can change the spanning tree topology.

6 panning ree Rules Root switch/bridge - ll ports of the root switch must be in forwarding mode. Root port - the root port on each switch must be set to forwarding mode. Designated port ports used to send or receive on a specific segment must be placed in forwarding mode. ll the other non-edge ports - must be placed in blocking mode. dge (ccess) ports remain in forwarding mode he addition or removal of links, trunks or Vlans triggers a spanning tree recalculation for that part of the network

7 1 R BRDG W D 100B (19) D ost xample D R W3 00B D 100B (19) 1GB (4) 1GB (4) D 1GB (4) R R D D W GB (4) D D W Default Priority 3768 ost 10 GB = 1GB = B = B =100

8 thernet Preamble synchronizes data at physical layer F start of frame ses addresses

9 ther hannel Hardware solution - lets you aggregate g up to 8 thernet trunks between two switches into a single thernet channel llows more than one path between switches because P sees a trunk as a single link voids the need for the 50 second P convergence ll trunks must be either blocking or forwarding because ether e channel treats them as a single trunk portfast puts a port immediately into forwarding should only be used on host (edge) ports

10 Rapid panning ree 80.1w - RP converges in anywhere from 1-0 seconds because it ignores everything except root, learning and forwarding ports when building the network topology

11 V Defines a broadcast domain based on logical criteria and is its own subnet and basically a security domain as well oftware based logical grouping independent of physical configuration here is complete isolation between V ach V has a unique D reated by assigning port numbers to the V Require a layer 3 device to communicate

12 ative V he native Vlan is an untagged Vlan and is the default Vlan for all untagged (no V D) traffic an only have one per trunk isco recommend using something other than Vlan 1 as native since Vlan 1 is the default Vlan and all ports are members of Vlan 1 by default Both ends must be set to the same value PV per Vlan spanning tree is a cisco proprietary protocol (RP is better)

13 V runking protocol that allows traffic from multiple Vlans to be carried between switches (nter-witch ink) isco proprietary trunk protocol only supported by cisco hardware that works on thernet, FDD or token ring 80.1Q standard thernet V trunking protocol

14 VP (V runking Protocol) V administration and management protocol reates VP domains an conserve bandwidth by limiting broadcasts, multicasts and other unicast packets with a process called pruning by not sending the packets from a specific V to any switch that has no ports configured for that V witch can only belong to one VP domain and the switches must be adjacent to each other

15 VP witch Roles VP erver maintains the V database VP lient receive information from the servers and can send and receive updates but cannot change the database ransparent does not participate in the VP domain. ll V created, deleted or edited are local to the switch and are not shared with other switches. se revision numbers to determine the current information and then overwrites the existing database. (problem?)

16 V DP runk odes n uto Desirable n yes yes yes uto yes no yes Desirable yes yes yes ccess no no no

17 Routing between Vs Require a router or level 3 switch to communicate between Vs ayer 3 switches provide much faster through put because they just put the packet on the port attached to the destination address

18 ther hannel Hardware solution - lets you aggregate g up to 8 thernet trunks between two switches into a single thernet channel llows more than one path between switches because P sees a trunk as a single link voids the need for the 50 second P convergence ll trunks must be either blocking or forwarding because ether e channel treats them as a single trunk portfast puts a port immediately into forwarding should only be used on host (edge) ports

19 Rapid panning ree 80.1w - RP converges in anywhere from 1-0 seconds because it ignores everything except root, learning and forwarding ports when building the network topology

20 witchport ecurity witchport security allows the administrator to configure which devices are allowed to use a port end information messages Discard frames hutdown the interface switchport port-security enables port security on the interface switchport port-security violation shutdown shuts down the interface if a violation is detected no shut enables the interface shutdown - nused ports should be administratively shut down otherwise a switch plugged into one will become part of the network

21 Duplex Port onfiguration Duplex must be the same on both ends of the cable Full / half mismatch won t work Full / auto negotiate auto side defaults to half - mismatch Half / auto negotiate auto defaults to half works uto negotiate / auto negotiate depends on cables (eg. GB defaults to full and 100bps defaults to half)

22 peed Port onfiguration Different speeds mismatch peed / auto will revert to lowest speed mismatch if different uto / auto each reverts to lowest speed mismatch if different