SD-Access fabric Packet Walk

SD-Access fabric Packet Walk

SD-Access fabric Packet Walk

SD-Access ARP Operation:

In SD-Access , the Fabric subnets resides on all fabric edge nodes due to which any endpoints within these subnets can resides anywhere in fabric. ARP operation in SD-Access fabric improves the efficiency of process in fabric deployment.

  • C1 wired client is connected to S1 and has got the IP address from DHCP.
  • C1 wants to communicate to C2 in same subnet which is connected to S2.
  • C1 sends the ARP request to find the MAC of C2
  • Once ARP is received by S1,
    • S1 Floods this ARP request, out to local ports in same VLAN
    • S1 also send the query to Control plane node to check whether it knows the MAC address of C2.
    • Control plane is aware of C2 MAC address and IP address and return this information to S1
    • S1 then queries to Control plane about location of C2 MAC address
    • Control plane will return the location of C2 which is S2.
    • S1 caches this information in its local cache to suppress any further query of C2.
    • S1 will replace the broadcast address from ARP request with MAC address of C2.
  • S1 encapsulates the ARP packet to VXLAN packet with Source IP of its own VTEP and Destination IP is VTEP IP of S2. Also S1 applies the specific policy context (VN, SGT) and then forwards this packet to S2.
  • Once S2 receives this packet and decapsulated it, as it know that the packet is for C2.
    • S2 then forwards the ARP request to C2
    • C2 looks the ARP request and respond its MAC address in ARP reply.
    • S2 will receives the ARP Reply and encapsulates it in VXLAN packet with Source IP of its VTEP and destination IP of S1 VTEP and forwards.
    • S1 will receives this packet, decapsulates it and forwards the ARP reply to C1.

Unicast Wired to Wireless Traffic Flow:

Refer Below Figure

  • Wired Client C1 connected to S1 and wireless client C2 on different subnet connected to fabric AP which is further connected to S2.
  • Both MAC and IP address of C1 and C2 are registered with fabric control plane node.
  • C1 now wants to communicate to C2and it will send IP packet with default gateway IP address as destination.
  • S1 receives this packet and queries for C2 location to fabric control plane node.
  • Control plane checks it database and returns the Location of C2 which is S2.
  • S1 then cache this information and applies the specific policy context (VN, SGT) and transmits the VXLAN frame to S2.
  • S2 receives this packet, decapsulates it and finds that C2 is connected to fabric AP.
  • S2 re-encapsulates the Packet to VXLAN with policy context (VN, SGT) and forwards it to AP.
  • AP upon receipt, decapsulates VXLAN packet and convert it to 802.11 format, then AP forwards the packet (via RF) to the wireless client.

Wireless Mobility Traffic flow:

In SD-Access fabric, Wireless Mobility is handled between WLC and fabric control plane node.


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