White Papers

57 Using MLAG in Dell Networking N-Series Switches | version 1.5
10 Connecting single-homed partners
By single-homing a device (attaching it to only one peer) does not actually create an MLAG partner. When
configuring an MLAG topology, partner devices (switches, servers, storage, or other) must use an MLAG link
aggregation that spans both MLAG peers in order to be a partner. Using only one cable or port-channel going
into only one of the MLAG peers (Figure 38) does not take advantage of the multiple path MLAG and can lead
to data loss.
MLAG peer
Peer-
Link
MLAG peer
X
X
Device A
Device B
Unsupported single-homed partner devices
Traffic to and from non-redundant ports is filtered and never crosses the MLAG peer link. Such ports/VLANs
need to obtain connectivity via an alternative to the MLAG-connected ports/VLANs. There are three ways to
circumvent the problem of a singled-homed device that allows it to attach and pass traffic through the MLAG
topology.
Solution 1
The first solution, as shown in Figure 39, is to attach single-homed devices to only one MLAG peer. An extra
port channel connection between the MLAG peers allows for non-MLAG VLAN traffic from the single-homed
devices to cross from one peer to the other. To prevent Spanning Tree Protocol from blocking one of these
ports, disable Spanning Tree Protocol from the extra port being added between the MLAG peers. In this
example, VLANs 1-39 are used in the MLAG, with VLAN 40 dedicated to be used only by devices with non-
redundant links. Attached devices achieve no MLAG benefits using this method.
MLAG peer
Peer-Link
MLAG
MLAG peer
Partner
Device
Device
VLAN 40
VLAN 40
VLAN 40 VLAN 40
VLANs 1-39
MSTP
Environment
Disable STP on this link
Solution 1 - Adding a VLAN link between the MLAG peers