Explain MLAG

Question 1

What is the Use Case of MLAG?

Answer 1

MLAG allows us to dual-home servers or downstream switches into two leaf switches while maintaining active/active forwarding without relying on Spanning Tree.

Question 2

Describe the MLAG Architecture?

Answer 2

• Each MLAG pair uses a dedicated peer-link.
• A control VLAN (e.g., VLAN 4092) is used for MLAG communication.
• VLAN 4092 is configured with L3 IPs on both switches.
• Port-Channel100 (Po100) is the peer-link interface.
• MAC addresses are synchronized across both MLAG switches.

Question 3

Walk Through a Design Principle of MLAG ?

Answer 3

• We assign consistent mlag <id> values to downstream Port-Channels.</id>
• The peer-link carries control traffic and BUM replication.
• If one leaf fails, the other continues forwarding without disruption.

Question 4

How does MLAG ties Into the EVPN-VXLAN fabric?

Answer 4

MLAG integrates into our EVPN-VXLAN leaf/spine architecture by providing host-level redundancy at the edge while VXLAN tunnels provide fabric-level redundancy.

Question 5

How do you use MLAG in your fabric?

Answer 5

• SPINEs act as EVPN route reflectors.
• Each leaf is a VTEP and runs iBGP with EVPN.
• Each leaf uses MLAG for server-facing interfaces with active/active redundancy.
• Each leaf uses anycast gateway on each leaf for localized L3 forwarding.
• VXLAN overlays carry tenant VLANs as VNIs.