2.1.a Implement and Troubleshoot Switch Administration Flash Cards

Here are my flash cards for 2.1.a Implement and troubleshoot Switch administration. I am giving these flash cards in TXT and in an ANKI package.

If you don’t have or know what Anki is, it is my favorite , free flash card program:

Here is the Anki package you may import and start using the flash cards right away:

What are the 7 fields that are in the ethernet frame? (excluding payload)
preamble (7 bytes)
start of frame delimiter (1 byte)

dst mac (6 bytes)
src mac (6 bytes)
.1Q tag (4 bytes)
ethertype (2 bytes)
Frame check sequence (4 bytes)
interpacket gap (12 bytes)

In the ethernet header, what is the preamble for?
Used to establish bit synchronization

In the ethernet header, what is the start of frame delimiter?
This field denotes that an ethernet frame is coming.

In the ethernet header, what is the .1Q header?
this field is used to indicate layer 2 qos and vlan membership

In the ethernet header, what is the ethertype field?
This field denotes what the next upper protocol is (0x0800 for IPv4)

In the ethernet header, what is the frame check sequence?
This is a checksum for the entire ethernet frame computed and checked by NICs.

In the ethernet header, what is interpacket gap?
It is a 12 Byte transmission after the frame ends which is to allow the receiver time to recover (buffers)

What is true about the FCS when using cut through switching?
Cut through switching does not check the FCS since it starts immedately sending the frame.

How many bits are MAC addresses?
48 bits

With respect to MAC, what is an OUI? Where is it?
An Organizational unique identifier (OUI) is the first 6 digits of a mac address, this sequence is assigned to NIC manufacterers which can be used to identify them.

When running “show mac address-table” what are the STATIC entires?
These entries are destination mac addresses that the device is listening on for certain processes and multicast addresses such as BPDUs, OSPF, EIGRP, DTP, etc… These have a port type of CPU.

How do we configure and verify disabling MAC learning on Cisco IOS?
Type it out
conf t
no mac-address-table learning
show mac address-table learning

How do you view the CAM table in Cisco IOS?
show mac address-table

What does err-disabled mean as it related to Cisco devices’ ports?
Err-disabled means the port is disabled from receiving traffic due to an issue or policy violation.

How do you view all ports AND an G0/1’s err-disabled status?
sho int status
show int g0/1 status
How do you manually recover an err-disabled port?
conf t
int g0/1
no shut

What 2 methods can you use to see why a port was err-disabled?
1. Check syslog or local log buffer via “show logging”
2. If errdisable recovery is on, it will tell you, use “”show errdisable recovery””

img 5a1626a9e4195

In the above I have enabled “errdisable recovery cause bpduguard”
How do you prevent a specific issue from putting a port into errdisabled? Ex.
Turn off link-flap
conf t
no errdisabled detect cause link-flap
NOTE: not all features can be turned off, ex: bpduguard errdisable cannot be turned off via this method

What show command will verify all of the errdisabled reasons enabled?
show errdisable detect

Is errdisable recovery turned on by default?
No, it is not, it should be enabled via “errdisable recover cause “

How do we change the timeout for errdisable recovery? How can we verify it?
conf t
errdisable recovery interval
sh errdisable recovery

How do switches learn mac addresses?
When a switch receives a frame on a port, it looks at the source mac address of the frame and maps that map address as reachable via this port. If that mac address was reachable via another port it has now moved to this port. These mac addresses can only have 1 port entry.

What is the default mac-address aging timeout?
300 sec or 5 min

What commands will change the CAM aging timeout and then verify it?
mac address-table aging-time
show mac address-table aging-time

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