DELL N3000 User Manual

Configuring Link Aggregation

The MLAG component internally configures filters so that traffic ingressing a 

peer-link is blocked from egress on the peer MLAG switch. The filters are 

modified when there is a failure of all the MLAG member interfaces on an 

MLAG switch and traffic must egress through selected ports on the MLAG 

peer. These filters block incoming traffic on all VLANs configured on the peer 

link, not just those configured as part of an MLAG. Therefore, there is no 

connectivity between non-redundant ports across the peer-link.

The MLAG component uses the keep-alive protocol to select a primary and a 

secondary switch. The keep-alive protocol is mandatory. The selection of the 

primary switch is non-preemptive and is not configurable.
Once elected, the primary switch owns the MLAG member ports on the 

secondary device. It handles the control plane functionality of supported 

protocols for the MLAG member ports on the secondary switch. Protocol 

status is not sent from the primary to the secondary switch. Always use the 

management interface on the primary switch to examine MLAG status.

MLAG peers exchange keep-alive packets over the peer-link. The keep-alive 

protocol is L2-based. Keep-alive messages are used for electing roles and to 

inform the MLAG peer that the MLAG switch is alive and functioning 

properly. The keep-alive protocol sends messages with an Ether-type of 

0x88E8 addressed to destination MAC 01:00:B5:00:00:00.

The MLAG component may optionally run the Dual Control Plane 

Detection Protocol (DCPDP) to detect the presence of the peer switch 

independently of the keep-alive protocol running on the peer link.
The Dual Control Plane Detection Protocol is a UDP-based L3 protocol. 

DCPDP may be configured on a routed VLAN that does not contain any 

MLAG port-channel interfaces. When enabled, the DCPDP sends an L3 

control plane detection message to the peer once every second. The message 

is unidirectional and contains the senders MAC address in the payload. The 

state of the primary and secondary MLAG switches is maintained on both 

MLAG peers.
DCPDP runs over an IP interface when enabled.