Link Aggregation Group - Summary- it address - It address two problems with Ethernet connections : Bandwidth limitation and lack of resilience- LAG is an umbrella term for : port trunking , link bundling , Ethernet/NIC bonding.- A LAG or Trunk may be created on the following mode:

- Static mode - Dynamic mode

- LACP - PAPG

Link Aggregation Control Protocol 802.3ad- LACP port trunks perform the same functions as static trunks- LACP provides a method to control the bundling of several physical ports to form a single logical channel- LAG's are used to increase the bandwidth between network devices by distribution the traffic load over multiple physical links- LACP LAG can operate in standby mode , if one port goes down another one can be activated to sustained the overall bandwidth - LACP Packets are sent with multicast group MAC Address 01:80:c2:00:00:02 , on all the LAG's interfaces - LACP can handle port-channel load-balance mode:

- a hash key mechanism (XOR operation) is used to load-balance frames across LAG interfaces as well as the input logical interface - default LAG algorithm is optimized for Layer 2 switching , using src-mac and dst-mac- in a Layer 2 switch, one link will end being over utilized and other links are underutilized- we can configure the hash to used also Layer 3 and 4 fields (src-ip , dst-ip , src-port and dst-port)

- LACP negotiation (Cisco): - Active:

- When trunk in active it is trying to bring up the LAG- it will send continuously LACPDU to initiate the LAG

- Passive: - it waits for the neighbor end to initiate the LAG creation- initially it doesn’t send LACPDU , once the LAG is formed then it will start to send LACPDU

- LACP Timeout: - Fast:

- the timeout period for receiving LACPDUs is 3 seconds, and the peer sends an LACPDU every second.

- Slow - The timeout period for receiving LACPDUs is 90 seconds, and the peer sends an LACPDU every 30 seconds.

- LACP defines the following parameters: - System Priority:

- use to decide which end LACP settings take precedence - the lower the value the higher the priority- is created from System Priority+ MAC address - the end with the highest priority is called Actor , its neighbor end will become Partner

- Port Priority Value : - used to determine which port is active and which is inactive- the lower the value the higher the priority

- the selection is performed by the Actor node / Highest priority

Multi Chassis LAG- it provides node and link level redundancy- usually used in CE interconnection- the CE is unaware of the MC-LAG , the configuration at CE level is as plain LAG configuration- in MC-LAG configuration one side should be active while the other side should be in passive mode ( Cisco case)- MC-LAG uses a control connection signaled over IP , so the two ends don't require direct connection- the MC-LAG Control Connection uses priority per box , the lowest the number the highest the priority of a node of becoming the Main node.- on the PE side both LAG ends should be configured in same way , sharing the same System ID - System Order :

- Placing the highest System ID on the PE side means that the PE side will become the Actor Node- the highest priority configured on the MC-LAG Control connection will determine the Master node and the Slave node.- the port priority on the Main node will determine the active ports .- in case there is a minimum active links configured and not satisfied by the Master node , traffic will be switched over the Slave Node.