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Dell Networking SONiC Multi-chassis Link Aggregation Group Terminology

Summary: This article explains the basic terminologies of Multi-chassis Link Aggregation Group (MC-LAG) in Dell Networking SONiC.

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Instructions

A port channel (LAG) allows the bundling of multiple interfaces together into an aggregate group for redundancy and increased bandwidth. All links are on the same switch. A Multi-chassis LAG (MC-LAG) allows the creation of a logical switch in which multiple interfaces on peer switches are bundled. The MC-LAG peer switches are managed separately as independent devices. The MC-LAG provides redundancy and load balancing between the MC-LAG peers. A downstream switch or server connects to the MC-LAG peer through an MC-LAG port channel.

Sample MCLAG Topology


Basic Terminologies

 

Terminology

Explanation

MC-LAG Domain
 		 Two peer switches connected with a keepalive and a peer link. One MC-LAG Domain supports two switches, and only one MC-LAG can be configured in a switch.

ICCP

Inter-Chassis Communication Protocol (ICCP) is the underlying protocol of MC-LAG. ICCP use TCP port 8888 to make the connection between MC-LAG peers. ICCP is defined in RFC7275. In Dell Networking SONiC MC-LAG Peer Keepalive link carries the ICCP messages. 

MC-LAG Peer

The other switch in the MC-LAG connected with the keepalive and peer links

MC-LAG Peer Link

The Link between two MC-LAG Peers - The link acts as data backup path between MC-LAG peers. It is used to carry data traffic when an MC-LAG member port is down. This can be a single link or Port Channel.

MC-LAG Peer Keepalive Link

MC-LAG Peer Keepalive Link is a Layer 3 link that connects MC-LAG peer switches. Ensure that the peer's Keepalive IP address is reachable from another peer. 
The best practice would be not to use Out Of Band Management interface IP address for MC-LAG Peer Keepalive Link. It would be ideal to use a L3 interface which has multiple links to reach peers keepalive IP address.  

MC-LAG Peer Keepalive link has the following functions.

  • It carries periodic heartbeat messages between MC-LAG peer devices to monitor their operational status. 
  • Control plane information like ARP, MAC between MC-LAG peer devices is synchronized through MC-LAG Peer Keepalive Link.
Orphan Port 
The orphan port is a Non-MC-LAG port. On an MC-LAG switch, port interfaces that are not configured as member interfaces in the MC-LAG, and which connect to downstream devices and belong to VLANs synchronized through the peer link, are orphan ports.
 

MC-LAG interface
 		 Member port interface on one of the peer switches that is assigned to the MC-LAG.



MC-LAG Peer Roles

  • One MC-LAG peer is chosen as Active and the other as Standby.
  • The IP address provided for MC-LAG Keepalive is used to elect Active and Standby. The switch with the lowest source-ip among the peers is chosen as Active and the other becomes standby.
  •  The Active Role is used in the control plane. However the data plane of both switches is independent.

Affected Products

Enterprise SONiC Distribution, PowerSwitch S6000 ON, PowerSwitch S4048T-ON, PowerSwitch S6010-ON, PowerSwitch S6100-ON, PowerSwitch Z9100-ON, PowerSwitch Z9332F-ON
Article Properties
Article Number: 000191238
Article Type: How To
Last Modified: 09 Apr 2024
Version:  4
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