🧩 What Does “Multiple (with virtual MAC)” Mean?
When you select “Treat
as Virtual IP Address”, you're telling Cisco ACI that this IP address
should be used as a shared gateway across multiple sites or pods.
To make this work, ACI uses a Virtual MAC address.
🔹 Why a Virtual MAC?
In a multi-site
or stretched fabric, the same IP address (e.g., 192.168.10.1) might be
configured in multiple locations. But MAC addresses are normally unique to each
site. If the same IP has different MACs in different sites, it can confuse
endpoints and break mobility.
So, ACI allows you to
assign a Virtual MAC to the VIP. This ensures:
- All sites use the same IP and MAC for
the gateway.
- Endpoints can move between sites without
needing to relearn the gateway MAC.
- Traffic flows seamlessly, even across
geographically separated data centers.
🧠 “Multiple” Refers To:
- You can have multiple subnets in
a BD marked as Virtual IPs.
- Each of these VIPs can share the same
Virtual MAC.
- This setup supports multiple
gateway IPs across sites, all behaving consistently.
📌 Example Scenario
Let’s say you have:
- DC1 and DC2 connected via ACI Multi-Site.
- A BD with subnet 10.1.1.1/24 used
as the gateway in both sites.
- You mark 10.1.1.1 as “Treat
as Virtual IP Address” and assign a Virtual MAC like 00:11:22:33:44:55.
Now:
- Both DC1 and DC2 advertise 10.1.1.1 with
the same MAC.
- VMs can move between sites without
changing their gateway.
- Network traffic remains stable and
predictable.
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