# Switch Interfaces

1.0 Network Fundamentals1.1 Explain the role and function of network components
1.1.b L2 and L3 switches1.4 Describe switching concepts
Configuring Speed, Duplex, and Description
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- autonegotiate○○What speed to useenabled by default  
    **duplex {auto | full | half} and speed {auto | 10 | 100 | 1000}** ○configure the speed and duplex settings  
    **(config** - add a text description to the interface **- int) # description** _text_  
    **show interfaces status** - lists port #, Name, status, vlan, duplex, speed, and type  
    a-full and aa-means that the listed speed and duplex values were autonegotiated.- 100

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IEEE autonegotiation (IEEE standard 802.3u)
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- each node states what it can do, and
- then each node picks the best options that both nodes support: -the fastest speed and the best duplex setting, with full duplex being better than half duplex.
- disable autonegotiation-Configure both the speed and duplex on a switch interface
- when a node tries to use autonegotiation but hears nothing from the device.  
    Speed: Use your slowest supported speed (often 10 Mbps).Duplex: If your speed = 10 or 100, use half duplex; otherwise, use full duplex.  
    Cisco switches can actually sense the speed used by other nodes, even without IEEE autonegotiation. -Cisco switches use this slightly different logic to choose the speed when autonegotiation fails:
- Speed: Sense the speed (without using autonegotiation), but if that fails, use the IEEE default (slowest supported speed, often 10 Mbps).
- Duplex: Use the IEEE defaults: If speed = 10 or 100, use half duplex; otherwise, use full duplex.
- -Ethernet interfaces using speeds faster than 1 Gbps always use full duplex.hubs do not react to autonegotiation messages

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Autonegotiation
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show interfaces and show interfaces description
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- -Line status = administratively downProtocol status = down
- Interface status = disabled

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Shutdown command is configured
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- -Line status = downProtocol status = down
- Interface status = notconnect

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Cable, speed mismatch, neighbor device is off , shutdown, or err-disabled
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- -Line status = upProtocol status = down
- Interface status = notconnect

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Not expected on LAN switch physical interfaces
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- -Line status = downProtocol status = down (err-disabled)
- Interface status = err-disabled

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Port security has disabled the interface
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- -Line status = upProtocol status = up
- Interface status = connected

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the interface is working
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show interfaces fa0/13 - -lists the speed and duplex for interface Fast Ethernet 0/13with nothing implying that the values were learned through autonegotiation.(without the status option)
speed manually set 10 Mbps on one switch and 100 Mbps on the other
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Quick Commands
Speed/ duplex
#duplex auto/full/half#speed auto/10/100/1000
Description
#description (text)
Interface
#show interfaces status#show interfaces fa0/3
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###### 7. Switch InterfacesWednesday, June 30, 2021 8:01 AM

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speed manually set 10 Mbps on one switch and 100 Mbps on the other-both switches would list the port in a down/down or notconnect state
if the duplex settings do not match-the switch interface will still be in a connected (up/up) or connected state.
How to identify duplex mismatch problems, --check the duplex setting on each end of the link to see if the values mismatch.watch for incrementing collision and late collision counters
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Common Layer 1 problems

- -receiving device might receive a frame whose bits have changed values.These frames do not pass the error detection logic as implemented in the FCS field in the Ethernet trailer,
- -The receiving device discards the frame and counts it as some kind of input error.Cisco switches list this error as a CRC error
    - -Frames that did not meet the minimum frame size requirement Can be caused by collisions.-(64 bytes, including the 18-byte destination MAC, source MAC, type, and FCS).  
        Runts:
- Frames that exceed the maximum frame size requirement -(1518 bytes, including the 18-byte destination MAC, source MAC, type, and FCS)  
    Giants:  
    Input Errors: -A total of many counters, including runts, giants, no buffer, CRC, frame, overrun, and ignored counts.  
    CRC: --Received frames that did not pass the FCS mathcan be caused by collisions
- -Received frames that have an illegal formatcan be caused by collisions.-(like ending with a partial byte)  
    Frame:

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Packets Output: -Total number of packets (frames) forwarded out the interface.
Output Errors: -Total number of packets (frames) that the switch port tried to transmit, but for which some problem occurred.
Collisions: -Counter of all collisions that occur when the interface is transmitting a frame
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- -The subset of all collisions that happen after the 64th byteOften point to a duplex mismatch-(In a properly working Ethernet LAN, collisions should occur within the first 64 bytes  
    Late Collisions:

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Collisions occur as a normal part of the halfa switch interface with an increasing collisions counter might not even have a problem. -duplex logic imposed by CSMA/CD
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- if the CRC errors grow, but the collisions counters do not, the problem might simply be interference on the cable.