Tshoot Notes: Layer 2 Technologies

VLANs 

- Layer 2 Broadcast Domain
- Data VLAN
- Voice VLAN (Auxilliary VLAN)
- VLAN1: default VLAN, Trunk Link - Native VLAN (untagged)
- Extended Range VLAN 1006 - 4094
- Extended Range VLANs prerequisite is VTP Transpartent mode

conf t
switchport mode access to configure for port access
switch access vlan 100 to assign vlan
switchport voice vlan XXX to assign voice vlan

#show vlan
#show vlan id XX
#show vlan brief

 TRUNK

- ISL
- 802.1Q - takes the frame and inserts a tag (a field of VLAN ID) + (a field for QOS)
- 802.1Q Native VLAN - VLAN1 (untagged)

DTP - dynamic trunk protocol

1. Categorize switches from core, access
2. Core switch will be dynamic desirable - forms trunk links
3. Access switch dynamic auto - auto forms with desirable

#switchport mode access dtp is off not for trunking
#switchport mode trunk dtp is on
#switchport mode dynamic desirable - will be trunk
#switchport mode dynamic auto - will be trunk if other side is desirable
#switchport no negotiate - turing off dtp process (can be use with either mode access or mode trunk)

[Does not work]
SW1
int fa 0/2
switchport trunk encap dot1q
switchport mode dynamic auto
SW2
int fa 0/2
switchport trunk encap dot1q
switchport mode dynamic auto

 [Trunking will work]
SW1int fa 0/2
switchport trunk encap dot1q
switchport mode dynamic desirable
SW2
int fa 0/2
switchport trunk encap dot1q
switchport mode dynamic auto

[Trunking will work - you need to try!]
SW1
int fa 0/2
switchport trunk encap dot1q
switchport mode trunk
switchport mode dynamic auto
SW2
int fa 0/2
switchport trunk encap dot1q
switchport mode trunk

[Trunking will work]
*Not having the same native vlan
SW1 - native vlan 10
SW2 - native vlan 20
[But will have inconsistencies if one of the VLAN20 is not same on SW1]


changing native vlan on other side
int fa 0/2
switchport trunk native vlan 20


[Trunking will work]
SW1
int fa 0/2
switchport trunk encap dot1q
switchport mode trunkswitchport nonegotiateSW2
switchport trunk encap dot1q
switchport mode trunk
switchport nonegotiate

[Will not work]
SW1
switchport trunk encap dot1q
switchport mode trunk
switchport nonegotiate SW2
int fa 0/2
switchport trunk encap dot1q
switchport mode trunk
switchport mode dynamic desirable

Things to remember for TRUNKING
1. Encapsulation mismatch
2. Native VLAN mismatch
3. Layer 1 - port shutdown
4. DTP misconfiguration
5. VTP and DTP relationships

#show int trunk
# show int fa0/1 switchport | ex private|unknown


 Troubleshooting VTP

VLAN Trunking Protocol = VLAN Management
VTP only works with trunks
To propogate VLAN information trunk links must be working

VTP Modes
1. Server - create and manage VLAN devices, propagate to servers and client
2. Client - slave to vtp server, cannot create and edit
3. Transparent - partipate in vtp domain, forward advertisement, not propagated
4. VTP off mode

#show vtp status - configuration revision

VTP Scenarios
1. Trunk
    - port are in access mode
    - incorrect vtp name
2. Domain Name / Password
    - mismatch vtp name --> change the vtp domain
    - mismatch password --> change the password
3. Overwrite versions
    - new swtich has higher revision --> change first to transparent
    - rename vtp domain
4. VTP version no 1 or 2
    - mismatch vtp version

#show cdp neighbors
#show int trunk
#show vlan brief | exclude 100
#show vtp status
#show vtp password

Changing VTP Domain Name (resetting revision numbers)
conf t
vtp domain Boyformat

Troubleshooting STP

1. 802.1D - IEEE
2. 802.1W - RSTP (rapid spanning tree protocol) - enable rapid PVST+
3. 802.1S - MSTP (built in behavior of RSTP)

STP Process
         
            dp        1GB     rp
[ SW1 ] --------------- [ SW4 ]
     |  rp                   nd |
     | 1GB                     | 100 MBPS 
     |  dp                  dp  |
[ SW2 ] --------------- [ SW3 ]
    RB dp         1GB     rp

1. Root Bridge - lowest bridge ID = Priority ID + VLAN ID + Lowest MAC Add
2. Non Root Bridge has a 1 Root Port (bandwidth higher)
3. Each Link has a Designated POrt
4. Non Designated Port

         
            dp        1GB     rp
[ SW1 ] --------------- [ SW4 ]
     |  rp                   nd |
     | 1GB                     | 100 MBPS 
     |  dp                  dp  |
[ SW2 ] --------------- [ SW3 ]
    RB dp         1GB     rp
1. Root Brige - Bridge Priority - Priority (Manual)
                                                  - Root Primary
2. Root Port - Manipulate Cost
3. Designated Port - Manipulate Cost

STP Toolkit
1. PortFast -
2. BPDU Guard -
3. Root Guard - superior bridge, no one can come in with lower priority
4. Loop Guard - stop normal convergence of STP

#show spanning-tree vlan 200
#show spanning-tree vlan 200 bridge
#show spanning-tree vlan 200 root
#show spanning-tree vlan 200 summary
#show spanning-tree vlan 200 details

1. Cost - Root
2. Bridge ID

1. Check for Bridge IDs
2. Check the Priorities

Troubleshooting MSTP


PVST - per vlan spanning tree - each vlan has its own topology
MST - 802.1S can implement only the exact numbers of topology
         - coexist with PVST

Fool-proof MST
1. Region Name
2. Revision Number
3. Instances - VLAN

#show spanning-tree mst 1

#show run | begin spanning tree
  - validate the region name (case sensitive)
  - revision number
  - instance

#conf t
#spanning-tree mst configuration
#name NAME OF REGION
#end

#conf t
#spanning-tree mst 1 root primary - manipulating priority
#spanning-tree mst 1 root secondary - backup

#show run | inc priority

Troubleshooting Etherchannel

Can be Layer 2 or Layer 3 (multilayer switches)

1. Shutdown the other side (to prevent err-disable)
    - err-disable sometimes require to make the configuration to default
2.  Both devices links are physically identical
3. Dynamic or Manual creation (ON:static / LACP: active, passive / PAGP: Auto,des)

#show etherchannel ? alot of verification commands

Creating etherchannel
1. Default the interfaces
#conf t
#default int range fa 0/1-6
#int range fa 0/1-6
#shutdown
#do show int status | include disabled
#switchport trunk encapsulation dot1q
#switchport mode trunk
#switchport trunk allowed vlan 10,20,30
#switchport trunk allowed vlan add 40 - additional vlan
#channel-group 1 mode active - LACP

#show int po1 switchport
#show etherchannel summary - show the ports on the bundle
#show int trunk#show spanning-tree vlan 10 (Cost 4 = 1000 / Cost 19 = 100)

#show etherchannel load-balance

2. Load Balancing
#conf t
#port-channel load-balance ? - shows the options/method for load balancing

#show cdp neighbors
#show etherchannel summary
#show int po1 switchport
#show run | inc FastEthernet|channel-group