ICND2 Flashcards
Two VLAN tagging protocols.
ISL- Cisco proprietary
802.1Q - Open IEEE
Static vs Dynamic VLAN
Static- Port is assigned a VLAN
Dynamic- VLAN is assigned according to MAC address connected to port. Use VMPS Vlan Management Policy Server.
What domain is each separate VLAN in?
Broadcast
Hosts in one VLAN cannot reach hosts in another VLAN, by default
A Layer 3 device is needed for inter-VLAN communication (this will be
covered later)
Each VLAN needs its own subnet, for example, VLAN 1 –
192.168.1.0/24, VLAN 2 – 192.168.2.0/24
All hosts in a VLAN should belong to the same subnet
Which VLAN is generally native by default?
VLAN 1
At what point are frames tagged with VLAN ID?
At trunk port based on access port it originated from.
Vlan tagging only occurs on the trunk, not access port. It just states that if the port is an access port and not trunk, the frame will not be tagged. The switch will strip off the vlan tag at the end of the trunk and switch it in hardware to the correct access port it needs to go to.
Is Native VLAN traffic tagged?
No.
3 types of switchports?
Access links or ports
Trunk links or ports
Dynamic (this will be discussed shortly)
How many VLANs can be created?
4096
VLAN 802.1Q trunking commands
Sw(config)#interface FastEthernet 0/1
Sw(config-if)#switchport
Sw(config-if)#switchport mode trunk
Sw(config-if)#switchport trunk encapsulation dot1q
5 trunk modes:
- On – forces the port into permanent trunking mode. The port becomes a trunk, even if the connected device does not agree to convert the link into a trunk link.
- Off – the link is not used as a trunk link, even if the connected device is set to “trunk.”
- Auto – the port is willing to become a trunk link. If the other device is set to “on” or “desirable,” then the link becomes a trunk link. If both sides are left as “auto,” then the link will never become a trunk, as neither side will attempt to convert.
- Desirable – the port actively tries to convert to a trunk
link. If the other device is set to “on,” “auto,” or “desirable,” then the link will become a trunk link. - No-negotiate – prevents the port from negotiating a trunk connection. It will be forced into an access or trunk mode as per the configuration.
Switchport: Auto -> Auto
Access
Switchport: Auto -> Desirable
Trunk
Switchport: Auto -> Trunk
Trunk
Switchport: Auto -> Access
Access
Switchport: Desirable -> Auto
Trunk
Switchport: Desirable -> Desirable
Trunk
Switchport: Desirable -> Trunk
Trunk
Switchport: Desirable -> Access
Access
Switchport: Trunk -> Auto
Trunk
Switchport: Trunk -> Desirable
Trunk
Switchport: Trunk -> Trunk
Trunk
Switchport: Trunk -> Access
Limited Connectivity
Switchport: Access -> Auto
Access
Switchport: Access -> Desirable
Access
Switchport: Access -> Trunk
Limited Connectivity
Switchport: Access -> Access
Access
Command show port trunk info. i.e auto, desirable
show interface trunk
or
show interfaces switchport
What file is VLAN info stored in?
VLAN.dat in flash memory.
SwitchA#dir flash:
Signs of duplex mismatches?
input and CRC errors on the interface
755 input errors, 739 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
Inter-VLAN routing not working:
Check to ensure that the link between the switches and the routers is set up correctly, and the relevant VLANs
are allowed and not pruned (see VTP pruning). The show interface trunk command will provide the required information. Also, check to ensure that the router’s sub interfaces are configured with correct encapsulation and
VLAN, and the sub interface’s IP address is the default gateway for the hosts.
VLANs cannot be created:
Check whether the VTP mode on the switch is
set to “client.” VLANs cannot be created if the VTP mode is client. Another important factor is the number of VLANs allowed on the switch.
The show vtp status command will provide the information required (see the Troubleshooting Trunking and VTP section below).
Hosts within the same VLAN cannot reach each other:
It is important that hosts in a VLAN have an IP address that belongs to the same subnet. If the subnet is different, then they will not be able to reach each other. Another factor to consider is whether the hosts are connected to the same switch. If they are not connected to the same switch, then ensure that the trunk
link(s) between the switches is/are working correctly and that the VLAN is not excluded/not pruned from the allowed list. The show interface trunk command will show needed information regarding the trunk link.
Commands to configure a voice vlan
SW1(config-vlan)#interface FastEthernet0/6
SW1(config-if)#switchport mode access
SW1(config-if)#switchport access vlan20
SW1(config-if)#switchport voice vlan10
Command to turn off DTP
switchport nonegotiate
Is DTP still on when you create a trunk port?
Yes. Must turn off with switchport nonegotiate
What is native VLAN used for?
used by the switch to carry specific protocol traffic, like Cisco Discovery Protocol (CDP), VLAN Trunking Protocol (VTP), Port Aggregation Protocol (PAgP), and Dynamic Trunking Protocol (DTP) information.
Commands to change trunk native VLAN
Switch(config)#interface FastEthernet0/1
Switch(config-if)#switchport trunk native vlan ?
Turning on VTP
Switch(config)#vtp mode server ‹this is on by default
Switch(config)#vtp domain in60days
Turning on VTP password
Switch(config)#vtp password Cisco321
Setting device VLAN database password to Cisco321
VTP modes
Server (default)
Client
Transparent
VTP Server
In Server mode, the switch is authorized to create, modify, and delete VLAN
information for the entire VTP domain. Any changes you make to a server
are propagated throughout the whole domain. VLAN configuration is stored
in the VLAN database file “vlan.dat” located on the flash memory.
VTP Client Mode
In Client mode, the switch will receive VTP information and apply any changes, but it does not allow adding, removing, or changing VLAN information on the switch. The client will also send the VTP packet received
out of its trunk ports. Remember that you cannot add a switch port on a VTP client switch to a VLAN that does not exist on the VTP server. VLAN configuration is stored in the VLAN database file “vlan.dat” located on the
flash memory
VTP Transparent Mode
In Transparent mode, the switch will forward the VTP information received out of its trunk ports, but it will not apply the changes. A VTP Transparent mode switch can create, modify, and delete VLANs, but the changes are not propagated to other switches. VTP Transparent mode also requires configuration of domain information. A VTP transparent switch is needed when a switch separating a VTP server and client needs to have a different VLAN database. Transparent mode is needed to configure the extended VLAN range (1006 to 4096).
How to reset VTP config number on switch
In order to reset the configuration revision of a switch,
change the VTP domain name, and then change the name back to the original name.
VTP configuration number
The configuration revision number is a 32-bit number that indicates the level
of revision for a VTP packet (see the show vtp status output above). This
information is used to determine whether the received information is more
recent than the current version.
If switch with higher VTP config # is connected to network it can wipe out all other VLAN database files and bring network down.
STP IEEE
IEEE 802.1D
STP Data units?
BPDU (Bride Protocol Data Unit) tagged with VLAN ID
How often are STP messages sent?
BPDUs sent every 2 seconds
How many Designated Ports can be on a LAN segment?
- That means if two are facing eachother, one must block.
STP Port States. How many? What are they?
Blocking – BPDUs received only (20 seconds)
Listening – BPDUs sent and received (15 seconds)
Learning – Bridging table is built (15 seconds)
Forwarding – Sending/receiving data
Disabled – Administratively down
Port State Movement
- From Initialization to Blocking
- From Blocking to either Listening or Disabled
- From Listening to either Learning or Disabled
- From Learning to either Forwarding or Disabled
- From Forwarding to Disabled
STP timer values
STP timers are used in the process to control convergence:
Hello – 2 seconds (time between each Configuration BPDU)
Forward Delay – 15 seconds (controls durations of Listening/Learning
states)
Max Age – 20 seconds (controls the duration of the Blocking state)
Default convergence time is 30 to 50 seconds.
STP Bride ID. Composed of what?
Priority (16 bits) + MAC Address (48 bits)
Default STP priority
32768
STP priority values multiplier value?
4096
Command to set switch as STP root?
spanning-tree vlan 2 root {primary | secondary}
spanning-tree vlan 2 priority 0
in increment of 4096 starting at 0
Metrics used in calculating STP.
Cost and Priority
Better is lower # based on better bandwidth
STP Root Port Election tiebreaker metrics
- Lowest Root Bridge ID
- Lowest Root path cost to Root Bridge
- Lowest sender Bridge ID
- Lowest sender Port ID