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Part 2 Cisco SD-Access: ARP Enhanced Forwarding

Cisco SD-Access: ARP Enhanced Forwarding

Earlier we discuss on the ARP flow within the SD-Access if we have the clients in the same subnet and not using the L2 flooding because control plane nodes know about the information of the client 2 within the fabric. 

When we are saying the ARP Enhanced Forwarding means instead of using the L2 all vlans in SDA fabric will use the L3 VNI of 4097

Fig 1.1-ARP Enhanced Forwarding

Step 1:  Client1 and Client2 belong to the same subnet and Client1 wants to communicate to Host 2. Since they are in the same subnet Client1 sends an ARP request for the mac-address of Client2

Step 2: As part of Enhanced forwarding ARP handling process the edge node 1 will proxy-arp for the Host 2 mac address and will send the mac-address of the “Anycast-GW” back to Client1.

Step 3: Once the ARP reply reaches Host 1 it will populate its ARP table and then will send the traffic out to edge node 1.

The packet will contain below:
SRC IP: Client1 IP 
SRC MAC: Client1 MAC
DST IP: Client2 IP
DST MAC: Anycast-GW MAC

Step 4: Now the traffic reaches edge node 1,the edge node 1 will ask the Control Plane node ”where is Host 2 located “ and based on the reply will forward it to the destination fabric node.

Step 5: After the map-reply is received the edge node 1 understands that is needs to send traffic to the edge node 2 . It encapsulates the traffic in VXLAN and using the l3 VNI is sent to the destination

The packet will contain below:
INNER PACKET:
SRC IP: Client1 IP 
DST IP: Client2 IP
SRC MAC: Client1 MAC
DST MAC: Anycast-GW MAC

OUTER PACKET:
SRC IP: Edge 1 IP 
SRC MAC: Router MAC
DST IP: Edge 2 IP
DST MAC: Next-Hop MAC (Intermediate node)

Step 6: Once Traffic reaches edge node 2 it will decapsulates the VXLAN headers and based on the Inner packet details will do a routing lookup to send it to Host 2.

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