SWITCH Study Notes – Basic Switch Operation & Configuration

Here are my notes from chapter one of Chris Bryant's (@ccie12933) BCMSN study guide and some of my own blending. I'm kind of breezing through much of the material not spending too much time, but just getting familiar with the general concepts again. It's been a long time since working with switching – about 3 years exactly! I more involved at  layer 3.

So if the notes seem a bit "light", take these as primer notes. I don't want to spend too much time here when I've got real SWITCH reading soon. I know, you're asking "why the hell waste your time there then?" – right? I briefly mentioned before why I'm going this route first instead of the CiscoPress reading. The reason is I always feel like I'm lost or don't know jack when it comes to reading Cisco Press material on something I'm not too familiar with. So Chris teaches in a very practical format and then I go to Cisco Press teach me the Cisco way

This approach worked well for me on the BSCI. I'll slowly post my notes (I'm up to chapter 5) daily until I catch up.

• Ethernet Types
  • Basic Ethernet
    • Based on IEEE 802.3
    • 10MB BW to users
    • Each port on a switch is its own collision domain
    • Uses UTP (unshielded twisted pair) cabling
    • 100 meter length max
  • Fast Ethernet (FE)
    • Defined in IEEE 802.3u
    • Operates at 100MB
    • Can use UTP or Fiber wiring
    • Full duplex FE total BW is 200 MBPS – FE ports send/receive at the same time
    • FE ports can operate in 10 or 100 MB
  • Gigabit Ethernet
    • Defined in IEEE 802.3z
    • Supports speeds up to 1000MBPS or 1 Gigabit Per Second (GBPS)
    • Cabling varies depending on the standard in use on your switch. Shielded Twisted Pair (STP), Multimode Fiber (MMF) and Single-Mode Fiber (SMF) are some possibilities
  • 10 Gigabit Ethernet
    • Defined in IEEE 802.3ae
    • Only works on fiber-optic cable and in full duplex mode
  • Long Range Ethernet (LRE)
    • Defined in IEEE 802.3ab
    • LRE can use preexisting phone wiring to provide Ethernet service
    • Available speed depends on cable length. The longer – the less bandwidth is available

• Cable review
  • To connect to the console port of a switch, you must use a rollover cable – requires a DB9 port
  • To connect a router, PC, or server to a switch – you need a straight through cable.
  • To connect a switch to another switch, you’ll need a cross-over cable

• Geebic
  • A module that fits into a Gig Ethernet port.
  • They are hot swappable
  • Used when migrating to a new media type

• How The Switch Builds Its MAC Table
  • The official terminology for the MAC table is the CAM table, or Content Addressable Memory table.
  • Switches use Layer 2 (MAC) addresses to forward or filter frames as needed
  • Switches can learn MAC addresses dynamically or statically – its more efficient to have the switch learn them dynamically
  • Switches learn dynamically by examining the source MAC first
  • It refers to its MAC / CAM table to determine if it already knows of the source. If not, it adds the source’s MAC and the port it can be reach on to its MAC / CAM table
  • It repeats the same process for the destination. One of the following can take place for the destination MAC
    • The destination MAC is a unicast and there is no entry for the address in the MAC table. This frame will be flooded – it will be sent out every switch port except the one it came in on
    • The destination MAC is a unicast and there is an entry for the address in the MAC table. In this case, the frame will be sent out only the port leading to the host with the proper destination MAC.
    • The destination MAC is a unicast, and there is an entry for the address in the MAC table, AND the source and destination address are off the same port. This frame will be filtered – it will not be forwarded at all by the switch
    • The destination MAC is a broadcast or multicast, in which case the frame will be sent out every port except the one it was received upon

• Assign an IP address to the switch's management interface (by default, the vlan 1 interface)
  • SWITCH_2(config)#interface vlan 1
  • SWITCH_2(config-if)#ip address 20.1.1.1 255.255.255.0

• The Interface Range And Description Commands
  • To choose a range of ports use the “interface range” command
    • SW2(config)#interface range fast 0/1 – 11
    • SW2(config-if-range)#speed 10
    • SW2(config-if-range)#duplex half
  • You can also use the “interface range’ command to describe ports as well.
    • SW2(config)#interface range fast 0/11 – 12
    • SW2(config-if-range)#description ports trunking with SW1

• The Errdisable Recovery Command
  • Ports will usually enter the state error-disabled or err-disabled under certain circumstances such as a violation of port security (802.1x)
  • Once a port enters this state, by default they must be manually reopened.
  • You can set the port to open on its own – autorecover – using the “errdisable recovery” command
    • SW2(config)#errdisable recovery cause all
    • SW2(config)#errdisable recovery interval ?
      <30-86400> timer-interval(sec)
    • SW2(config)#errdisable recovery interval 300

Any corrections or additions are greatly appreciated! You can download a copy of these notes by clicking the "Printer Friendly" below.

Cheers!

@LBSources