DELL N3000 User Manual

Configuring Link Aggregation

DCPDP is intended to provide a secondary layer of protection against peer 

link failures. If the peer-link goes down but the DCPDP protocol is enabled 

and remains up, the MLAG links on the MLAG secondary peer are disabled. 

If the peer-link is restored, a new primary switch is elected, the primary switch 

assumes control over the secondary peer, and the MLAG links are brought up.
In the case where there are no keep-alive messages detected from the peer and 

DCPDP is disabled, but both peer units remain up, two primary switches 

result, each with a unique MAC address, and each operating over its part of 

the former MLAG. In this situation, the selection of dynamic or static LAGs 

determines the MLAG behavior.
On a peer-link failure with DCPDP disabled and the MLAG configured with 

dynamic LAGs to the partners, traffic forwarding continues through the 

primary MLAG switch. LACP running on the partner device detects that the 

port-channel connected to the secondary MLAG switch is sending LACPDUs 

with a different system ID and brings down the links connected to secondary 

MLAG peer. This behavior reduces or eliminates spanning tree reconvergence 

due to the MLAG switches sending BPDUs with different bridge IDs to the 

partner switch.
On a peer-link failure with DCPDP disabled and the MLAG configured with 

static LAGs to the partners, traffic forwarding continues through both the 

primary and secondary MLAG switches. Spanning tree sends BPDUs with 

different bridge IDs to the partner switch, resulting in serial spanning tree 

reconvergence. For this reason, dynamic MLAGs are strongly recommended.

This section describes how to configure two MLAG peers in a basic L2 

switching configuration with the default spanning-tree configuration.

1 Enable MLAG globally and create the MLAG VLANs:

feature vpc

vlan 10-17

exit

2 Configure the keep-alive protocol:

Configure the device priority using the role command, if desired. This 

should be configured differently for each of the MLAG peers.