DELL N3000 User Manual

Configuring Link Aggregation

the case where a link from the router to one of the MLAG peers fails. Static 

routes must be added to the primary and secondary MLAG peers to route 

traffic addressed to the connected router across the backup routed link in the 

case of a failure of an MLAG link to the router.
This is not a recommended topology, as the same scenario can be achieved 

without the use of MLAG by simply configuring the middle switches as 

routers and using ECMP to load-balance across the links to the redundant 

router pair. In this type of solution, MLAG adds no value, as the redundancy 

is provided by L3 routing, not by the MLAG.

In the one-armed scenario in Figure 28-16, the MLAG cannot associate the 

failure of the VLAN 30 link with VLAN 20. Traffic from the routed or 

switched network towards the upstream router is routed over the backup 

router link when the MLAG link fails solely based on the routing 

configuration. Traffic from the upstream router on VLAN 30 to the 

switched/routed network is handled by the MLAG failover scenario and is 

switched across the peer-link on VLAN 30, but it could just as easily be 

handled by L3 routing.

Peer-Link

MLAG

VLAN 30

VLAN 20

VLAN 30
IP address 192.168.30.1/24

Failed Link

VLAN 10
IP address 192.168.10.1/24
IP route 192.168.30.1 192.168.20.1 200

VLAN 10
IP address 192.168.10.2/24
IP route 192.168.30.1 192.168.10.1 200

VLAN 20

16

8

IP rout