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
- 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
IEEE autonegotiation (IEEE standard 802.3u)
- 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
Autonegotiation
show interfaces and show interfaces description
- -Line status = administratively downProtocol status = down
- Interface status = disabled
Shutdown command is configured
- -Line status = downProtocol status = down
- Interface status = notconnect
Cable, speed mismatch, neighbor device is off , shutdown, or err-disabled
- -Line status = upProtocol status = down
- Interface status = notconnect
Not expected on LAN switch physical interfaces
- -Line status = downProtocol status = down (err-disabled)
- Interface status = err-disabled
Port security has disabled the interface
- -Line status = upProtocol status = up
- Interface status = connected
the interface is working
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
Quick Commands Speed/ duplex #duplex auto/full/half#speed auto/10/100/1000 Description #description (text) Interface #show interfaces status#show interfaces fa0/3
###### 7. Switch InterfacesWednesday, June 30, 2021 8:01 AM
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
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:
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
- -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:
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
- if the CRC errors grow, but the collisions counters do not, the problem might simply be interference on the cable.