DELL N3000 User Manual

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Configuring Link Aggregation
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L3 VLAN Termination on MLAG Not Supported
In the “two-armed” fully routed scenario shown in Figure 28-14, both the 
routed network and the switched network are in the MLAG. Switched traffic 
to and from the upstream network is automatically unblocked over the peer-
link when an MLAG link fails. But, because the failed link is part of an L3 
port-channel (with a unique VLAN), the peer-link does not automatically 
unblock the downstream routed VLANs (which are not correlated with the 
upstream MLAG VLANs) across the peer link. Specifically, MLAG does not 
correlate the failure in VLAN 30 with VLAN 20. This leads to a black hole. 
Adding a backup routed link solves the black hole issue, but it also makes the 
MLAG solution unnecessary. L3-routed VLAN termination on the MLAG 
peers is not supported—VLANs must extend across the MLAG peers to two 
MLAG partners.
Figure 28-14. L3 VLAN Termination on MLAG, Example 1
MLAG Router Peer
MLAG Router Peer
Peer-Link
MLAG
Router
MLAG
VLAN 30
Failed Link
Switched Network
Only
VLAN 20