What is LACP?
This is Standards-based (IEEE 802.3ad) negotiation protocol. Link Aggregation Control Protocol, is used to dynamically build an EtherChannel. There are different modes of LACP.
- Active: The active end of the group sends out a LACP frame and initiates the negotiation to form the EtherChannel. Both ends could be active and the result would be the same.
- Passive: Passive Mode does not initiate the negotiation. It just responds to LACP packets initiated by other end. So if both ends were passive, the EtherChannel would not be formed.
What is PAgP?
This is Cisco proprietary negotiation protocol. Port Aggregation Protocol is used to achieve the same goal as LACP. PAgP has 2 modes:
- Desirable: In this mode, the negotiation will be initiated by sending the special frames to form EtherChannel with the other end.
- Auto: In this mode, negotiation is not initiated. It only responds to the special frames received for negotiation form the other end. So, if both ends are in Auto mode, EtherChannel would not be formed.
There is basically no difference between the two other than the names of the mode.
One thing to note is that there is no particular command to enable LACP or PAgP on a Cisco router. Instead, the mode names are used.
For example: If you use Desirable mode, then the router understands that you are implementing PAgP and if you use Active mode, the router will understand that you're trying to use LACP.
One thing to note is that there is no particular command to enable LACP or PAgP on a Cisco router. Instead, the mode names are used.
For example: If you use Desirable mode, then the router understands that you are implementing PAgP and if you use Active mode, the router will understand that you're trying to use LACP.
Ether Channel Modes
-------------------------------------------------------------------------------------------------
Mode Protocol Description
-------------------------------------------------------------------------------------------------
Auto | PAGP | Sets the interface to respond to PAgP negotiation packets, but
the interface will start negotiations on its own.
Desirable | PAGP | Sets the interface to actively attempt to negotiate a PAgP
connection.
On | EtherChannel | Forces the connection to bring all links up without using a
protocol to negotiate connections. This mode can only connect to
another device that is also set to on. When using this mode, the
switch does not negotiate the link using either PAgP or LACP.
Active | LACP | Sets the interface to actively attempt to negotiate connections
with other LACP devices.
Passive | LACP | Sets the interface to respond to LACP data if it receives
negotiation requests from other systems.
----------------------------------------------------------------------------------------------------------------
EtherChannel Configuration:
- Conf t
- interface range fastEthernet 0/1 - 2
- speed auto
- duplex full
- switchport trunk encapsulation dot1q
- switchport mode trunk
- channel-group 10 mode desirable
SW2
- Conf t
- interface range fastEthernet 0/1 - 2
- speed auto
- duplex full
- switchport trunk encapsulation dot1q
- switchport mode trunk
- channel-group 20 mode auto
- sh ip inter br
- sh etherchannel summary
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use f - failed to allocate aggregator
u - unsuitable for bundling
w - waiting to be aggregated
d - default port
Number of channel-groups in use: 1
Number of aggregators: 1
Group Port-channel Protocol Ports
------+-------------+-----------+----------------------------------------------
10 Po10(SU) PAgP Fa0/1(I) Fa0/2(I)
SW2
- sh ip inter br
- sh etherchannel summary
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use f - failed to allocate aggregator
u - unsuitable for bundling
w - waiting to be aggregated
d - default port
Number of channel-groups in use: 1
Number of aggregators: 1
Group Port-channel Protocol Ports
------+-------------+-----------+----------------------------------------------
20 Po20(SU) LACP Fa0/1(I) Fa0/2(I)
- show etherchannel port-channelChannel-group listing:
----------------------
Group: 20
----------
Port-channels in the group:
---------------------------
Port-channel: Po20 (Primary Aggregator)
------------
Age of the Port-channel = 00d:00h:11m:53s
Logical slot/port = 2/20 Number of ports = 0
GC = 0x00000000 HotStandBy port = null
Port state = Port-channel
Protocol = PAGP
Port Security = Disabled
- show interfaces Port-channel 20 (To check bandwidth of etherchannel)
Hardware is EtherChannel, address is 00e0.b008.3130 (bia 00e0.b008.3130)
MTU 1500 bytes, BW 500000 Kbit, DLY 1000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Half-duplex, 500Mb/s
input flow-control is off, output flow-control is off
Members in this channel: Fa0/1 ,Fa0/2 ,Fa0/3 ,Fa0/4 ,
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:08, output 00:00:05, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
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