Link Aggregation Group (LAG)
Link Aggregation takes place on point to point connections between two devices.In a link Aggregation physical ports are bundled up together to increase the uplink bandwidth and it provides availability, since it contains multiple links if one links fails one link will be utilised during the same duration.
Link Aggregation at Layer 2 is called Ether Channel while Link Aggregation or dynamic link aggregation could take place at with the help of protocols PaGP(Port Aggregation Protocol) or LACP(Link Aggregation Control Protocol).
If we have two ISP links used in a network of 20Mb each and our network bandwidth utilisation is increased to more than 20Mb, so rather increase in link utilisation we can do link aggregation and make it as 40Mb single link. We can load balance traffic with the help of Link Aggregation.
Layer 2 Link Aggregation:
Ether Channel: It is a Cisco term of bundling two or more Ethernet links for the purpose of aggregating available bandwidth and physical redundancy.A maximum of 8 ports can be bundled up with the help of Ether Channel of same bandwidth in to is eight ratio.
Lets say we have 100Mb link, then maximum capacity of Ether channel group is 800Mb.
Ether channel conditions:
1. Bundled ports must belong to the same vlan.
2. If used as a trunk, bundled ports should be in trunking mode and in native vlan.
3. Each port should have same speed and duplex mode.
4. All bundlled ports should have identical spanning tree settings.
Ether Channel utilises the Hashing algortithm in which we do XOR operations of the last bit/s of octet to be used for communication. Let us assume we need to pass traffic from 192.1682.1.1 to 172.16.119.32 and we have aggregated two links.
Then for 192.168.1.1 last bit of last octet is 1 which is 001 in binary.
similarly, 172.16.119.32 las bit of las octet is 2 which is 010 in binary.
so XOR operation of 1 XOR 0 become 011 which equals to 1, so link which has index 1 will be utilised and viceversa.
so if four links are used we used 01 XOR 10 which becomes 11 which eqauls to 3. so the link which has index figure 3 will be utilised and the same for 8links.
Ques:What if IP frames are not sent over Ether Channeles or i mean layer 2 is used only?
Ans: Then lowest machanism is used which is MAC address based port aggregation.
Ques: How loops avoids in Ether Channel?
Ans: No inbound broadcasts or multicast are sent back to the other ports used in port channel. Outbound broadcast and multicast frames are load balancing lik any other.
Configuring ETher Channel on cisco:
SW1(config-if-range)#int range f0/1 -2
SW1(config-if-range)#exit
SW1(config)#interface range f0/1 - 2
SW1(config-if-range)#switchport trunk encap dot1q
SW1(config-if-range)#switchport mode trunk
SW1(config-if-range)#channel-group 10 mode active
SW1(config-if-range)#end
Configurinf the LAG on Juniper device
set chassis aggregated-devices ethernet device-count 50
set interfaces xe-0/1/0 ether-options 802.3ad ae0
set interfaces xe-3/1/0 ether-options 802.3ad ae0
set interfaces ae0 aggregated-ether-options lacp active
set interfaces ae0 unit 0 family ethernet-switching port-mode trunk
set interfaces ae0 unit 0 family ethernet-switching vlan members all
set class-of-service interfaces ae0 scheduler-map ezqos-voip-sched-maps
Reference: http://kb.juniper.net/InfoCenter/index?page=content&id=KB11431
PaGp and LACP are dynamic link aggregation protocols where PaGP is cisco propietary and LACP is open standard.
LACP:
Link Aggregation Control Protocol is the standard 802.3ad. You combine multiple links into a single logical link to increase bandwidth and redundancy. All links participating in a single logical link must have the same settings such as duplex mode, link speed, and interface mode such as access or trunk.
You can have up to 16 ports in an LACP EtherChannel but only eight can be active at one time.
LACP can be configured in either passive or active mode. In active mode, the port actively tries to bring up LACP. In passive mode, it does not initiate the negotiation of LACP.
Here are a few parameters which can be configured with LACP ports:
System Priority – Forms the system ID and is used during negotiation.
Port Priority – Used to decide which ports should be put in standby mode when there is a limitation or something preventing a port from aggregating.
Administrative Key – Defines the ability of a port to aggregate with other ports.
In the event one of the links within an LACP bundle fails, traffic continues to flow on the other available links in the bundle.
PaGP:
Cisco’s proprietary alternative to LACP, Port Aggregation Protocol. It also creates Etherchannel links and is configured similarly to LACP.
Configuring PAgP properly and it will automatically configure individual ports into a single logical link.
There are two modes for PAgP:
auto – This is the passive negotiating state which responds to PAgP packets.
desirable – Places interface into an active negotiating state.
Having two ends of a PAgP link in auto mode will not result in a PAgP link because neither will negotiate to bring up the PAgP EtherChannel.
PAgP protocol data units (PDUs) are sent and received on the lowest numbered VLAN of the trunk link.
You can have up to eight ports in a single PAgP EtherChannel.
Just like LACP, all ports in a PAgP EtherChannel must have the same speed and duplex settings.
Having two ends of a PAgP link in auto mode will not result in a PAgP link because neither will negotiate to bring up the PAgP EtherChannel. PAgP protocol data units (PDUs) are sent and received on the lowest numbered VLAN of the trunk link.
You can have up to eight ports in a single PAgP EtherChannel. Just like LACP, all ports in a PAgP EtherChannel must have the same speed and duplex settings.
Configuring PaGP at cisco Switch:
SW1(config)#interface range f0/1 - 2
SW1(config-if-range)#switchport trunk encapsulation dot1q
SW1(config-if-range)#switchport mode trunk
SW1(config-if-range)#channel-group 10 mode desirable
SW1(config-if-range)#end
Link Aggregation takes place on point to point connections between two devices.In a link Aggregation physical ports are bundled up together to increase the uplink bandwidth and it provides availability, since it contains multiple links if one links fails one link will be utilised during the same duration.
Link Aggregation at Layer 2 is called Ether Channel while Link Aggregation or dynamic link aggregation could take place at with the help of protocols PaGP(Port Aggregation Protocol) or LACP(Link Aggregation Control Protocol).
If we have two ISP links used in a network of 20Mb each and our network bandwidth utilisation is increased to more than 20Mb, so rather increase in link utilisation we can do link aggregation and make it as 40Mb single link. We can load balance traffic with the help of Link Aggregation.
Layer 2 Link Aggregation:
Ether Channel: It is a Cisco term of bundling two or more Ethernet links for the purpose of aggregating available bandwidth and physical redundancy.A maximum of 8 ports can be bundled up with the help of Ether Channel of same bandwidth in to is eight ratio.
Lets say we have 100Mb link, then maximum capacity of Ether channel group is 800Mb.
Ether channel conditions:
1. Bundled ports must belong to the same vlan.
2. If used as a trunk, bundled ports should be in trunking mode and in native vlan.
3. Each port should have same speed and duplex mode.
4. All bundlled ports should have identical spanning tree settings.
Ether Channel utilises the Hashing algortithm in which we do XOR operations of the last bit/s of octet to be used for communication. Let us assume we need to pass traffic from 192.1682.1.1 to 172.16.119.32 and we have aggregated two links.
Then for 192.168.1.1 last bit of last octet is 1 which is 001 in binary.
similarly, 172.16.119.32 las bit of las octet is 2 which is 010 in binary.
so XOR operation of 1 XOR 0 become 011 which equals to 1, so link which has index 1 will be utilised and viceversa.
so if four links are used we used 01 XOR 10 which becomes 11 which eqauls to 3. so the link which has index figure 3 will be utilised and the same for 8links.
Ques:What if IP frames are not sent over Ether Channeles or i mean layer 2 is used only?
Ans: Then lowest machanism is used which is MAC address based port aggregation.
Ques: How loops avoids in Ether Channel?
Ans: No inbound broadcasts or multicast are sent back to the other ports used in port channel. Outbound broadcast and multicast frames are load balancing lik any other.
Configuring ETher Channel on cisco:
SW1(config-if-range)#int range f0/1 -2
SW1(config-if-range)#exit
SW1(config)#interface range f0/1 - 2
SW1(config-if-range)#switchport trunk encap dot1q
SW1(config-if-range)#switchport mode trunk
SW1(config-if-range)#channel-group 10 mode active
SW1(config-if-range)#end
Configurinf the LAG on Juniper device
set chassis aggregated-devices ethernet device-count 50
set interfaces xe-0/1/0 ether-options 802.3ad ae0
set interfaces xe-3/1/0 ether-options 802.3ad ae0
set interfaces ae0 aggregated-ether-options lacp active
set interfaces ae0 unit 0 family ethernet-switching port-mode trunk
set interfaces ae0 unit 0 family ethernet-switching vlan members all
set class-of-service interfaces ae0 scheduler-map ezqos-voip-sched-maps
Reference: http://kb.juniper.net/InfoCenter/index?page=content&id=KB11431
PaGp and LACP are dynamic link aggregation protocols where PaGP is cisco propietary and LACP is open standard.
LACP:
Link Aggregation Control Protocol is the standard 802.3ad. You combine multiple links into a single logical link to increase bandwidth and redundancy. All links participating in a single logical link must have the same settings such as duplex mode, link speed, and interface mode such as access or trunk.
You can have up to 16 ports in an LACP EtherChannel but only eight can be active at one time.
LACP can be configured in either passive or active mode. In active mode, the port actively tries to bring up LACP. In passive mode, it does not initiate the negotiation of LACP.
Here are a few parameters which can be configured with LACP ports:
System Priority – Forms the system ID and is used during negotiation.
Port Priority – Used to decide which ports should be put in standby mode when there is a limitation or something preventing a port from aggregating.
Administrative Key – Defines the ability of a port to aggregate with other ports.
In the event one of the links within an LACP bundle fails, traffic continues to flow on the other available links in the bundle.
PaGP:
Cisco’s proprietary alternative to LACP, Port Aggregation Protocol. It also creates Etherchannel links and is configured similarly to LACP.
Configuring PAgP properly and it will automatically configure individual ports into a single logical link.
There are two modes for PAgP:
auto – This is the passive negotiating state which responds to PAgP packets.
desirable – Places interface into an active negotiating state.
Having two ends of a PAgP link in auto mode will not result in a PAgP link because neither will negotiate to bring up the PAgP EtherChannel.
PAgP protocol data units (PDUs) are sent and received on the lowest numbered VLAN of the trunk link.
You can have up to eight ports in a single PAgP EtherChannel.
Just like LACP, all ports in a PAgP EtherChannel must have the same speed and duplex settings.
Having two ends of a PAgP link in auto mode will not result in a PAgP link because neither will negotiate to bring up the PAgP EtherChannel. PAgP protocol data units (PDUs) are sent and received on the lowest numbered VLAN of the trunk link.
You can have up to eight ports in a single PAgP EtherChannel. Just like LACP, all ports in a PAgP EtherChannel must have the same speed and duplex settings.
Configuring PaGP at cisco Switch:
SW1(config)#interface range f0/1 - 2
SW1(config-if-range)#switchport trunk encapsulation dot1q
SW1(config-if-range)#switchport mode trunk
SW1(config-if-range)#channel-group 10 mode desirable
SW1(config-if-range)#end
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