BGP EVPN VXLAN Intra VNI Communication - MAC-IP Learning Process

BGP EVPN VXLAN Intra VNI Communication - MAC-IP Learning Process

BGP EVPN VXLAN  Intra VNI Communication - MAC-IP  Learning Process

In this section , we will see how Local VTEP Switch learns the Ip address of its connected Host and how Host Mobility manager component install this information in L2RIB of the Specific VNI. L2RIB will contain MAC-IP address information and this L2RIB is also called as IP VRF.

Below figure explains MAC-IP learning Process

All the learning process has been divided on phases , lets discuss all phases one by one.

Phase 1: Local VTEP ARP Table:

When machine CAFE comes UP , It will send the GRAP packet , upon receipt , Local VTEP Leaf-101 stores the MAC-IP binding information in to its ARP table. This can be very well verified by showing ARP table under VRF

Phase 2-3: MAC IP On Local VTEP

HMM ( Host mobility manager ) after learning the MAC/IP information as Local Route , Installs this information in to local Host database and forwards the MAC-IP information in to L2RIB.

The Local Database contains below information :

  • IP address /32
  • MAC Address
  • SVI
  • Local Interface

The L2RIB also has same information without SVI.

Below figure shows how host CAFÉ  MAC/IP information is stored in Local host Database ( HMM RIB) of VRF TENEANT 55

Below figure also shows that the information concerning MAC/IP of CAFÉ in IP VRF in L2RIB is produced by HMM Component.

Phase 4: BGP Route EXPORT on Local VTEP

VTEP Leaf-101 installs MAC/IP route from L2RIB to BGP loc-RIB and then is advertised as a separate BGP EVPN Route type 2 advertisement – means dedicated updates for both MAC only and MAC/IP NLRI

The difference in carried NLRI information between MAC-Only and MAC-IP route advertisement is that later one has also host IP address and mask information as well as an additional MPLS Label Stack 2 information, that defines the L3VNI used in VRF TENANT55. There are also two additional Extended Communities; RT 65000:10055 and Router MAC 5e00.0000.0007 carried within the update.

Below are the attributes that will be advertised by local VTEP along with MAC-IP NLRI .

  • [2] - BGP EVPN Route-Type 2, MAC/IP Advertisement Route
  • [0] - Ethernet Segment Identifier (ESI), all zeroed out = single homed site
  • [0] - Ethernet Tag Id, EVPN routes must use value 0
  • [48] - Length of MAC address
  • [1000.0010.beef] - MAC address
  • [32] - Length of IP address
  • [] - Carried IP address
  • /272 - Length of the MAC-IP VRF NLRI in bits: RD (8 octets) + MAC address (6 octets) + L2VNI Id (3 octets) + L3VNI Id (3 octets) + IP address (4 octets) ESI (10 octets) = 34 octets = 272 bits.

There are also three BGP Extended Communities path attributes advertised with NLRI.

  • Route-Target: 65000:10000 - Used for export/Import policy (L2VNI)
  • Route-Target: 65000:10055 - Used for export/Import policy (L3VNI)
  • Encapsulation 8: Defines the encapsulation type VXLAN (Data Plane)
  • Router MAC: 5e00.0000.0007 - Used for Inner MAC Header source address for routed packets. This is needed because VXLAN is MAC in IP/UDP encapsulation tunneling mechanism and data payload over L3 border does not carry source host MAC address information. This is where the RMAC is used.

Phase 5: BGP Route Import on Remote VTEP

When VTEP Switch Leaf-102 receives the BGP EVPN MAC route advertisement and installs it to BGP Adj-RIB-In database without any modification. Leaf-102 imports the route in Loc-RIB and based on best path selection process, it is then installed in to L2RIB and while installing, Leaf-102 changes the RD value to based on BGP RID and VLAN ID.

Below is the output of BGP-RIB on Leaf-102 (Adj-RIB-In, Loc-RIB) . The first marked part shows original, unmodified NLRI received from Spine-11.

The Second highlighted part shows same NLRI installed in to Loc-RIB with Modified RD Value , The import is based on highlighted RT 65000:10000. The third highlighted part describes the same NLRI and is installed with RD ( used for Inter-VNI traffic L3VNI).

Phase 6: IP VRF on Remote VTEP:

Remote VTEP verifies the reachability of Next Hop IP address found from NLRI and since it is hit , L2FWDER installs the MAC-IP route in to L2RIB.


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