Identify interface and cable issues Flashcards
Collision Domains
Each switchport creates a collision domain
How to tell if collisions are occuring
Symptom: Slow down of traffic
Triage:
show interfaces (can see all collisions)
Can also look into the packets
Info seen in show interfaces
Is interface up (layer 1)
Is line protocol up (layer 2)
Determine if layers are up
Layer 1 - show interface - is interface up?
Layer 2 - show interface - is protocol up?
Layer 3 - ping/traceroute/show ip route
show int shows up/up
L1 and L2 are connected
show int shows admin down down
shutdown (do no shut to reenable
show int shows down / down
No cable
Bad cable
Wrong cable pin out
Speed mismatch
Neighbor dev is powered off/shutdown/or error disable
up / down
Not expected on LAN switch physical inteface
maybe on loopback or vlan (virtual interface)
show int shows down / down (err-disabled)
Port security has disabled interface
Feature on switchport to secure port
Input errors
Counters increase when interface gets frame with any kind of error - includes runts, giants, no buffer available, CRC errors.
Output errors
Increase when sends frame with error, including runts, giants, no buffer, CRC error
Runts
ethernet frames less than 64 bytes
Giants
Ethernet frames that exceed IEEE 802.3 frame size (1518 bytes, no jumbo frames) and have incorrect FSC
throttles
when interface fails to buffer incoming packet
CRC errors
Cyclic Redundancy Check errors
Checksum generated doesnt match checksum that receiver calculated
Usually means cabling issues or defective card
