MLAG

The following topology has a pair of server clusters that are dual-homed to a pair of VXLAN gateways with three tenants:

VXLAN Gateways with Three Tenants

Traffic from the tenant VMs that are part of an MLAG can hash toward either gateway node. This can result in GW3 learning the same VM‘s MAC from different VTEPs. To avoid MAC toggling on remote VTEPs, ExtremeXOS requires that users configure a special local tunnel endpoint address on MLAG nodes that will be used for tenant VLANs that have MLAG ports.

For a configuraiton example, see Configuration Example for MLAG.

Additional considerations:

Since the tenant VLAN IDs can be reused ExtremeXOS needs to allow multiple VLANs with the same tag to be dual homed using the same MLAG peers. This requires tenant traffic be encapsulated over the ISC link to help distinguish traffic from different tenant VLANs.
Only one copy of BUM traffic from a tenant VM should be forwarded to the network.
MLAG peers have a mechanism in place to block BUM traffic coming from the network to not be sent back into the network through the other peers.
When one of the MLAG peers loses connectivity to the underlay network, reachability can be established through the ISC. This requires you to configure an underlay VLAN that includes the ISC ports and run a routing protocol over the ISC. Using the correct metric values ensures that this VLAN is not preferred by the peers to reach remote nodes during steady state and would be used only when all other connectivity to the underlay network is down.
Note
Multi-peer MLAG is not supported.
MLAG with alternate IP configuration, disables the local MLAG ports when the MLAG peer is alive, but the ISC port alone goes down. This feature is used to prevent duplication of packets if MLAG peers are part of larger L2 domain. For VXLAN, MLAG peers connect to an L3 cloud on their upstream (northbound) interface and they share the same LTEP IP address. Other VTEPs use L3 ECMP to send traffic to one of the MLAG peers. With an alternate IP configured and ISC going down, traffic hashing towards an MLAG peer, which disabled its MLAG ports, results in dropped traffic. So it is recommended not to configure MLAG alternate IP feature on VXLAN VTEPs.
Note
In a VXLAN and MLAG environment where a node has two MLAG peers, even when MLAG alternate IP address is not configured, traffic disruption likely occurs when an ISC connection is lost between any of the MLAG peers.

Published March 1, 2020prev | next

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