Separate machines into separate collision domains that would exist if they were connected via a hub / directly. This means multiple machines can transmit / receive.
Contain MAC table which is filled when data is sent from a new host. If a switch does not know the destination it sends data out of all ports.
Switches are transparent bridges; do not modify frames. Switches use Application Specific Integrated Circuits ASIC (hardware) whereas bridges use software.
MAC table stored in Content Addressable Memory (CAM) which is a piece of hardware.
Auto at both ends will not work properly, unless a desirable mode is set. Default on switch is Auto. It is best to set 100MB F/d if that is what is needed.
A Switch only ever has a single IP in the native VLAN.
All ports are disabled by default; use no shutdown to enable them and shutdown to disable.
Used to eliminate loops and provide redundancy; without it:
· Broadcast Storm
· Unstable MAC Table Entries
· Duplicate packets
· Only one root bridge per network
· All ports on root bridge are designated
· Non-root bridges have a root port
· Each Segment (collision domain) has a designated port
Each bridge has an ID, the switch with the lowest ID is root.
STP is running By Default on all switches
Spanning-tree blocks all ports by default.
RSTP is much faster, and if f/d assumes that port is an edge-port.
Spanning Tree cont.
Default switch priority is 8000, thus the switch with the lowest MAC address will be root.
Based on path cost:
· 10 Gb – 2
· 1 Gb – 4
· 100Mb – 19
· 10 Mb – 100
Bridge Protocol Data Units – BPDU’s:
Root bridge sends BPDU’s every 2 seconds. If 10 are missed spanning-tree re-evaluates the network; this can take 30-50 seconds.
BPDU data is sent on the default VLAN.
Contain ID of Root, ID of Source, Path Cost
Blocking > Listening > Learning > Forwarding
It is possible to block different ports on different VLAN’s; spreading the load across switches.
Spanning Tree config.
To view current spanning-tree info:
# show spanning tree
This will display if the switch is the root bridge and what the spanning-tree status is for the active ports.
To view spanning-tree info per VLAN:
# show spanning-tree vlan 101
To show spanning-tree info per interface:
# show spanning-tree interface eth 0/1
To set a port as an edge-port:
(config)# int fastethernet 0/1
(config-if)# spanning-tree portfast
Port speed can be set for path cost using:
(config-if)# speed 100
(config-if)# duplex full
To view interface configuration:
# show interface fastethernet 0/1
· Static – assigned per port. One VLAN only per port.
· Dynamic – sever controls membership database consisting of every MAC Address.
Cisco switches support two types of VLAN:
· 802.1q – industry standard, tags frames. Up to 4096 VLAN’s.
· ISL – Cisco proprietary, encapsulates frame. Up to 1024 VLAN’s.
Default Native VLAN on Cisco hardware = 1
With ISAL all VLAN’s are tagged, with 802.1q the native VLAN is not tagged.
The native VLAN must be configured to be the same on all switches within a network.
Dynamic VLAN’s not commonly used due to administrative nightmare involved.
To create a VLAN:
# vlan database
# vlan 101
Will only apply VLAN’s when you exit VLAN d/b.
To assign a VLAN an IP:
# int vlan 101
# ip address 10.1.1.1 255.255.255.0
To assign a port to a vlan:
(config)# int fastethernet 0/1
# switchport access vlan 101
View VLAN information:
# show vlans / show vlan 100
# show ip interface brief
On newer switches it is possible to configure VLANS using:
(config)# vlan 100
The Configuration register specifies start-up mode:
· 2142 – Ignore startup-config
· 2102 – Boot normally
· 2101 – Boot ROM OS
Switches have several types of memory
· Flash – where IOS / IOS Image is stored
· ROM – where bootstrap / mini IOS is stored.
· NVRAM – where startup-config is stored.
VTY’s will only work when a password is set:
# line vty 0 4 – sets p/w for first 4 vty’s
# password password_here
Console – from global config:
# enable secret – encrypted
# enable password – clear text
Boot process: – Interrupt using Ctrl-C / Break
POST > Boot Strap > Config Register > IOS > NVRAM
Trunks – VLAN Trunking Protocol
· Server – can edit VLAN d/b, will send / receive adverts.
· Client – cannot edit d/b, will receive adverts.
· Transparent – will not send / receive adverts, can edit d/b.
All switches by default are Servers. This must be changed!
Requires a trunk to be setup between switches. Trunk carries all VTP data.
# vtp domain name_here
# vtp password pass_here
# vtp mode server / client etc
(config)# interface fastethernet 0/24
(config-if)# switchport mode trunk