Advertising and Learning Multihomed MAC Addresses and Snooped ARP Entries
Multihomed Media Access Control (MAC) and
MAC/IP refers to a local MAC address or a snooped Address Resolution Protocol (ARP)
entry
that has been learned over a local Ethernet Segment (ES). In singlehomed (SH) scenarios,
locally learned MAC entries are advertised by Route Type-2 (RT-2). Upon processing
the
route, the receiver learns about the egress Virtual Tunnel Endpoint (VTEP) for the
MAC, but
it does not have information about the egress port on the egress VTEP.
In multihomed (MH) scenarios, MH MAC and MAC/IP information is also carried in the same RT-2 message, but it includes the Ethernet Segment Identifier (ESI) for the ES associated with the MAC entry. This means that, in addition to the egress VTEP, the remote VTEP is aware of the outgoing ES on the egress VTEP. This information is then used in features such as aliasing and fast-convergence.
The table below outlines the fundamental elements of MAC/IP routes or RT-2 for MH:
MAC/IP Route or Type-2 (RT-2) for SH and MH
| Message | Description |
|---|---|
| RD (8B) | Route Distinguisher (RD) for the Ethernet Virtual Instance (EVI). This is the same in both SH and MH scenarios. |
| ESI (10B) | ESI. For SH MAC, this value is always set to 0. For MH MAC, the ESI value is included. |
| Key: Ethernet Tag ID (4B) | Identifier for the Ethernet Tag. This is the same in both SH and MH scenarios. |
| Key: MAC Address Length (1B) | Length of the MAC address. This is the same in both SH and MH scenarios. |
| Key: MAC Address (6B) | The actual MAC address. This is the same in both SH and MH scenarios. |
| Key: IP Address Length (1B) | Length of the IP address. This is the same in both SH and MH scenarios. |
| Key: IP Address | The actual IP address. This is the same in both SH and MH scenarios. |
| Label1/L2VNI | Label for Layer 2 Virtual Network Identifier (VNI). This is the same in both SH and MH scenarios. |
| Label2/L3VNI | Label for Layer 3 VNI. This is the same in both SH and MH scenarios. |
| EVI-RT Extended Community | Extended community for the EVI Route Target (RT). This is the same in both SH and MH scenarios. |