Cisco - Switch Port Configuration

Ethernet Overview

  • Determining Bandwidth Requirements
    • Types of applications used
    • Traffic flow in use
    • Size of user community
  • Links between access, distribution and core should be scaled to match required load
  • Ethernet based on IEEE 802.3 standard
  • A shared medium becoming both a collision and broadcast domain
  • Based on Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
  • More “Crowded” segments likely to suffer more collisions and therefore operate ineffectively
  • switching eliminates the collection problem by dividing a single segment into multiple segments, each port is a unique collision domain
  • Hosts/stations can operate in full duplex when using switched, effectively doubling bandwidth.

Scaling Ethernet

  • Originally 10Mbps per segment
  • 100Mbps, 1Gbps, 10Gbps, 40Gbps and 160Gbps standard exist
  • Fast Ethernet (100Mbps)
    • Supported on UTP, STP and fibre-optic cables
    • UTP/STP limited to 100 Metres
    • 62.5/125 Multimode fibre (MMF) supported 400 Metres (half-duplex) or 2000M (Full Duplex)
    • Single Mode fibre (SMF) max 10KM
    • Can be bundled into etherchannels to increase bandwidth
  • Gigabit Ethernet (1Gbps)
    • Uses same 802.3 frame format
    • Physical later modified to increase transmission speeds
    • Merges 802.3 and ANSI X3T11 Fibre Channel Standards
    • Supported on STP up to 2M (1000Base-CX)
    • UTP Cat 5 upto 100M (1000Base-T)
    • Fibre Optic
      • 1000Base-SX MMF 62.5 (275M) or 50 (550M)
      • 1000Base-LX/LH MMF 62.5 (550M) or 50 (550M), SMF 9 (10KM)
      • 1000Base-ZX SMF 9 (70KM), 8 (100KM)
    • “Gigabit over copper” switch ports can operate at 10/100Mbps or 1Gbps
    • Gigabit Ethernet offers up to 16Gbps (Full Duplex)
  • 10-Gigabit Ethernet (10Gbps)
    • Layer 2 details unchanged
    • Uses different transceivers - Physical Mediia Dependant (PMD) Interfaces
    • LAN PHY - Connects switches to Campus (Core) Layer
    • WAN PHY - Connects existing SONET/SDH, typically found in Metropolitan Area Networks (MAN)
    • PMD Interfaces use “10GBASE” prefix
    • Runs over MMF (33M - 330M)
    • Runs over SMF (10KM)
    • Copper: CX4 with Infiniband (15M)
    • Transceiver Types
      • Wavelength - S = Short, L = Long, E = Extra Long
      • PHY Type - R = LAN PHY, W = WAN PHY
      • LX4/LW4 Long Wave length, X/W indicate the coding used, 4 is number of wavelengths
      • WWDM = Wide Wavelength Division Multiplexing
  • Beyond 10-Gigabit Ethernet
    • 40Gbps bonds 4 x 10Gbps using a Quad SFP+ Module (QSFP+)
    • 100Gbps bonds multiple channels/lanes
    • 40/160Gbps defined in 802.3ba Standard

Duplex Operation Over Ethernet

  • Max throughput only possible when one device is connected to switch port
  • Switch ports are capabble of negotiating both speed and duplex, both ports muust be configured for auto-negotiation
  • Link speed is determined by electrical signaling, highest common speed is used
  • Duplex mode involves and exchange of information. Both ports must be auto otherwise half-duplex is the default
  • Errors on a link will occur when there is a duplex mismatch
  • Cisco recommendation is to use manual setings in order to avoid unusable connections
  • Catalyst switches 10/100/1000 auto sensing ports using RJ-45 connections with UTP cable
  • UTP cabling uses 4 pairs (Pins 1/2, 3/6, 4/5, 7/8) to connect straight through to other end
  • Gigabit provides SFP modules
    • Hot swappable
    • LC/MT-RJ Fibre Optic, RJ45 UTP Copper connectors
  • 10 Gigabit Ethernet uses X2 and SFP+ modules

Configuring Switch ports

  • Performed through global configuration mode

Selecting a single switch port

interface <type> <memmber>/<module>/<number>

Selecting multiple ports

interface range <name> , <name-2> [, <name-x>]
  <commands>

or

interface range <name> - <name>
  <commands>

Using Interface macros

define interface-range <name> [ , <name> ] [ - <name>]
interface range macro <name>
  <commands>

Adding Comments to interfaces

interface <name>
  description <one-line-string>

Manually setting port speed

interface <name>
  speed {10|100|1000|auto}

Manually setting duplex mode

interface <name>
 duplex {auto|full|half}

Managing Error Conditions On Switch Ports

General notes on error Conditions

  • Network management applications can poll devices to check for errors
  • Catalyst switches can detect errors an take action automatically
  • By default switches will detect errors on every port for all causes
  • By default switch ports must be manually shutdown then restored in order to recover
  • Ports are disabled for 300 seconds by default if automatically error recovery is enabled

Tune trigger clauses globally

[no] errdisable detect cause {all | <cause>}

Enable Auto Recovery

errdisable recovery cause {all | <cause>}

Change recovery timer

errdisable recovery interval <seconds>

Troubleshooting Port Connectivity

Check Port State - Up/Up is expected for normal operation

show interfaces [<name>]

Get Summary of all switch port states

show interface status

Show ports in error disabled states

show interface status err-disabled

Checking for speed/duplex mismatches

  • Check for error count greater than 0
  • “Runts” are packets truncated before being fully received
  • Input” errors usually show
  • Check if running at half-duplex, indicating unsuccessful auto-negotiation

Discovering Connected Devices

Cisco Discovery Protocol

  • Automated method for devices to advertise prescense to directly connected neighbors
  • Cisco propietary feature
  • One-Way, no response expected
  • Sent at the Data Link Layer (Layer 2) every 60 seconds
  • Information advertised
    • Hostname
    • Connected Interface
    • Device Capabilities
    • Hardware Platform
    • Software Version
    • Duplex Mode
    • Power Info
    • Management IP(s)
  • Cisco routers and switches have CDP enabled by default

See advertised neighbours

show cdp neighbors [<interface-name>] [detail]

Disable/Enable CDP globally on the switch

[no] cdp run

Disable/Enable CDP per interface

[no] cdp enable

View CDP info for named device

show cdp entry <name>

Using Power Over Ethernet (POE)

  • PoE can be used to provide power to IP phones and wireless access points (WAPs)
  • Provide a means of centralised power management, unlike using individual wall warts
  • PoE can be managed, monitored and offerred only to known devices
  • Best Practice: Connect switch to UPS so power can be maintained in the event of a power outage

How PoE Works

  • Switches must be rated to supply power to external devices
  • PoE methods
    • Cisco Inlne Power (ILP) - Cisco proprietary upto 7W
    • IEEE 802.3AF (PoE) up to 15.4W
    • IEEE 802.3AT (PoE+) up to 25.5W
    • Cisco Universal Power (UPoE) - Cisco propertiary up to 60W

Detecting A Powered Device

  • Power is disabled when port is down
  • Small voltage is sent across transmit/receive pairs
  • Resistance is measured and if detected a device must be present
  • Resistance values determine a specific power clauses
    • Class 0 - Default (15.4W)
    • Class 1 - 4.0W
    • Class 2 - 7.0W
    • Class 3 - 15.4W
    • Class 4 (802.3AT) - Upto 30W
  • Class 0 used when device/switch does not attempt discovery
  • Max of 15.4W is usually offered
  • CDP/LLDP can be used to request power up to 30W
  • Special TLVs used with CDP/LLDP for UPoE (Catalyst 4500 only)

Configuring PoE

  • General Notes
    • By default each port auto-detects if power is needed
    • If a device requests more power than configued, a log message is generated and port remains in non-connected state

Configure Power offered on a port

power inline auto [max <milliwatts>]
power inline static
power inline never

Verifying PoE

** Monitor power available/used/total **

show power inline [module <member>] [detail]
show power inline [<interface-name>] [detail]