notes: EtherChannel

EtherChannel
- bundles redundant links and treat them as a single link to achieving substantial
bandwidth and redundancy benefits.

-Notice that EtherChannel affects STP because ordinarily one or more of the links would be disabled to prevent a loop.

Guidelines for EtherChannel:
1. All Ethernet interfaces on all modules must support EtherChannel.
2. You have a maximum of eight interfaces per EtherChannel.
3. The ports do not need to be contiguous or on the same module.
4. All ports in the EtherChannel must be set for the same speed and duplex.
5. Enable all interfaces in the EtherChannel.
6. An EtherChannel will not form if one of the ports is a Switched Port Analyzer (SPAN) destination.
7. For Layer 3 EtherChannels, assign a Layer 3 address to the port-channel logical interface, not the physical interfaces.
8. Assign all EtherChannel ports to the same VLAN or ensure they are all set to the same trunk encapsulation and trunk mode.
9. The same allowed range of VLANs must be configured on all ports in an EtherChannel.
10. Interfaces with different STP port path costs can form an EtherChannel.
11. After an EtherChannel has been configured, a configuration made to the physical interfaces affects the physical interfaces only.

EtherChannel load balancing can use MAC addresses, IP addresses, or Layer 4 port numbers—either source, destination, or both source and destination addresses.


Etherchannel Load-Balancing options command:

port-channel load-balance {mode}

dst-ip Destination IP Address.
dst-mac Destination MAC Address(Default for IPv4 and non-IP traffic).
src-dst-ip Source XOR Destination IP Address.
src-dst-mac Source XOR Destination MAC Address.
src-ip Source IP Address (Default for IPv6 traffic).
src-mac Source MAC Address.


EtherChannel Modes:

1. On - no negotiation/non dynamic
2. PagP - cisco proprietary
- desirable - send
- auto - listen
3. LACP - ieee 802.3ad
-active - send
-passive - listen


layer 2 EtherChannel configuration set:

int range fa0/1-2
shutdown
switchport trunk encapsulation dot1q
switchport mode trunk
channel-group 1 mode desirable
no shut
!
interface port-channel1
switchport trunk encapsulation dot1q
switchport mode trunk

layer 2 EtherChannel configuration set:

int range fa0/1-2
shutdown
no switchport
channel-group 1 mode active
!
int Port-Channel1
ip address 1.1.1.1 255.255.255.0
!
int range fa0/1-2
no shutdown

verification command:

show etherchannel summary

SU - for layer 2/in used
RU - for layer 3/in used

notes: VTP Vlan Trunking Protocol

VTP- Vlan Trunking Protocol - is a Cisco proprietary Layer 2 multicast messaging protocol that synchronizes VLAN information across all media types and tagging methods on your switches.

You must configure the VTP domain name identically on each device; domain names are case-sensitive.
1. The switches must be adjacent.
2. The switches must be connected with trunk links.
3. The same VTP password must be configured if used in the domain

Versions

Version3 - enhanced, supports the use of extended VLAN range.

Version1,2 - supports md5 authentication and pruning.

VTP has four possible message types:
1. Summary advertisements
2. Subset advertisements
3. Advertisement requests
4. VTP Join messages (used for pruning)


VTP Modes:

1. Server: Enables you to create, modify, and delete VLANs; these changes are advertised to VTP Client mode systems; Catalyst switches default to this mode.
- VLAN configuration is stored in the VLAN database file called vlan.dat and is located on flash (const_nvram).
- VLANs 2-1000 are configurable.

2. Client: Does not enable the creation, modification, or deletion of VLANs on the local device; VLAN configurations are synchronized from Server mode systems.
- VLAN configuration is stored in the VLAN database file called vlan.dat and is located on flash (const_nvram).

3. Transparent: Permits the addition, deletion, and modification of VLAN information, but the information resides only locally on the Transparent device; these systems forward advertisements from servers but do not process them.
- Transparent mode is needed to configure extended VLAN range (1006-4096).
-If the domain name matches the locally configured domain name, a VTP version-2 transparent switch will transparently relay
transmitted TLV updates between switches, but a VTP version-1 transparent switch will drop those TLV updates.
- VLAN add/removes in the VTP domain does not affect transparent switches as the updates are not stored.
- A revision of 0 indicates a transparent mode switch is not participating in the update sequence of the VTP domain.
Note: pruning will be problem w transparent in the middle of client server.

VTP Revision number

The VTP configuration revision number is important. This value determines whether a switch has stale information about VLANs and ultimately controls whether the switch overwrites its VLAN database with new information.
The revision number increments each time a change is made to the VLAN database on a Server mode VTP system. The number is from 0 to 4,294,967,295.

WARNING: When introducing new Server mode switches, ensure that you do not inadvertently overwrite the VLAN database because of a higher configuration revision number on the new switch. Introducing new switches in Transparent mode helps ensure that this problem never results.

command to configure VTP:

vtp mode server
vtp mode domain-name

Authentication
-domain name is required
-ensure that md5 and passwords are the same

command:

vtp password pwd

VTP Pruning - enables you to limit the amount of traffic sent on trunk ports. It limits the distribution of flooded frames to only switches that have members of the particular VLAN.
- Eliminates the need to statically remove VLANs from trunk links where they not needed, this is done by having the switches automatically communicate with each other which VLANs they have locally assigned or are in the transit path for.
- this also reduces broadcast traffic.
- all vlan are pruned by default except the default vlan1


command:

vtp pruning

- vtp pruning can be configured only on vtp server and it will automatically propagate within the vtp domain.

VTP Pruning eligible list
- select VLANs you choose prune-ineligible
- Removing a VLAN from the "prune eligible list" forces the switch to receive traffic for that VLAN.
- ONLY VLANs 2-1000 are "prune eligible", the 5 default VLANs (1, 1002-1005) and extended VLANs cannot be pruned off an interface.

example command:

switchport trunk pruning vlan 2-11,13-1001

- Vlan 10 removed from the prune eligible list means. So traffic for VLAN 10 will be received.

notes: Switchport : access, trunk, dtp, vlan

Layer 2 ports

1. access ports - default port configuration, belongs to one VLAN
2. trunk ports - carries multiple VLANs.

Layer 3 Routed Ports

1. Switched Virtual Interfaces (SVI) - Logical layer3 VLAN interface.
-use as a management interface and as gateway for VLAN subnets.
2. Native routed interfaces - Using switch ports as a standard layer 3 ports. This features is only available on L3 switches.

command to configure switch interface:
no switchport
ip address 1.1.1.1 255.255.255.0

Trunks

1. ISL - Cisco proprietary.
- traffic is encapsulated within a 30-bytes ISL frame (26-byte header and 4-byte trailer).
Configured with "sw trunk encapsulation isl".

2. 802.1q - Open standard.
- All traffic are tagged with 4-byte 802.1q, except the 'native' VLAN.
- The native VLAN is a VLAN for which frames are not tagged. Following are the aspects of the native VLAN:

1. The VLAN a port is in when not trunking.
2. The VLAN from which frames are sent untagged on an 802.1Q port.
3. The VLAN to which frames are forwarded if received untagged on an 802.1Q port.

Cisco switches produce errors if the native VLAN does not match at each end of the link.
The default native VLAN in Cisco devices is VLAN 1.

You can control the 802.1Q VLAN traffic sent over a trunk, which is possible for security purposes or load balancing.

The command that creates and controls trunks on Cisco IOS-based switches is the interface command:

switchport trunk {allowed vlan vlan-list} | {encapsulation {dot1q | isl | negotiate}} | {native vlan
vlan-id} | {pruning vlan vlan-list}

trunking mode:

1. Static Trunk - hardcode a port as a trunk
Command:
switchport mode trunk

2. DTP (Dynamic Trunking Protocol) -is a Cisco proprietary protocol that negotiates the trunking status of a switchport
- enabled by default

DTP port states

1. auto: Enables the switch to create a trunk if initiated from the other switch. A switch programmed with auto does not initiate a trunk but can form a trunk if the other side initiates. The trunk is formed with desirable and on.
2. desirable: Actively tries to create a trunk link with the peer. The trunk is formed with auto, desirable, and on.
3. on: DTP messages are sent, and a trunk will be formed unless the peer explicitly forbids it. The trunk is formed with auto, desirable, and on.
4. off: Trunking is not allowed on the switchport regardless of the DTP status of the peer.
nonegotiate: Disables DTP and will not form a trunk link with a peer which requires trunk negotiation. Trunk is formed with on and nonegotiate

platform default dtp port states

3550 - desirable
3560 - auto

command to disable dtp:
switchport nonenegotiate

Setting the interface to static mode with "sw mode access|trunk" will not disable DTP negotiations.

VLAN

global command

vlan #
name vlan-name
exit
Note: you must exit for the vlan to be created.

command to activate vlan
vlan config mode
state active

Allowed-list
- Limits which VLANs are allowed on a specific trunk link.