UMR application in Ethernet VPN(EVPN)

In DCI scenario, if multiple DCs are interconnected into a single EVI, each DC will have to import all of the MAC addresses from each of the other DCs. . In addition, in user authentication scenario, a large number of users send authentication packets to the aggregation device through the access device, as a result, there are large scale of MAC addresses on RRs and aggregation devices. This document describes the use of the Unknown MAC-route(UMR). The solution advertises an unknown MAC-route (UMR) route instead of advertising all specific MAC routes and reducing the MAC scale. However, since the solution only sends UMR routes instead of advertising specific MAC routes, the MAC mobility function of EVPN cannot take effect normally. In particular, this document describes a MAC mobility procedure in UMR scenario.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. "GW": Gateway or Data Center Gateway "DC": Data Center "NVE": Network Virtualization Edge "UMR": Unknown MAC Route "I-ES and I-ESI": Interconnect Ethernet Segment and Interconnect Ethernet Segment Identifier. An I-ES is defined on the GWs for multihoming to/from the WAN.

1. All the MAC addresses are learned on NVE1/NVE2 within DC should advertised to DC's GW device accrording EVPN MAC/IP routes in the control plane. 2. All the MAC addresses are learned on NVE within DC should advertised to the other NVE that in the same DC, so that the NVE to NVE that in the same DC communication is always direct and does not go through the GW. 3. The MAC addresses are learned on NVE should not advertised to the other NVE that in the different DC. 4. The DC's GW advertise UMR route to NVE1/NVE2 instead of advertising the specific MAC in order to reduce the device's routes pressure. The UMR route is defined in and is a regular EVPN MAC/IP advertisement route in which the MAC address length is set to 48, the MAC address is set to 0, and the ESI field is set to DC's GW I-ES. 5. NVE1/NVE2 need to understand and process the UMR route, send frame to GW. Then GW will forward the packet to correct NVE.

As shown above, since GW only sends UMR routes to NVE devices, NVE will not import the MAC addresses of NVEs in different DCs. When the MAC of DC1 migrates from NVE1 to DC2’s NVE2, NVE1 will not perceive this migration and keep learning the MAC that has migrated to NVE2. As a result, the frame traffic to MAC from GW may go to wrong site.

Step1: The user first goes online from NVE1, NVE1 learns the user's MAC1, and advertise EVPN MAC1 route to GW. Step2: The GW receives the MAC1 route from NVE1, installs MAC1 to the local MAC-VRF table which the next hop of MAC1 is NVE1. Since it only sends UMR routes to NVE, it will not send EVPN MAC1 route to NVE2. Step3: The user migrates to NVE2 and goes online. NVE2 learns the user's MAC1 and advertise EVPN MAC1 route to GW. Step4: The GW receives the MAC1 route from NVE2, which has the same prefix as the MAC1 route from NVE1, as a result, the GW will form load balancing MAC-VRF table. Step5: As a result, the frame traffic sent to MAC1 via the GW may be sent to NVE1 by mistake until MAC1 on NVE1 ages out.

In order to solve this mac migration issue, the GW SHOULD advertise the MAC route to the NVE when the GW detect the MAC has been migrated. There are two scenarios as follows. 1. One of the scenario: Step1: When the GW receives MAC routes that have the same prefix, rather than different next hop and different ESI, the following conclusion can be drawn, which the MAC has been migrated. At the same time, the GW only send UMR route. Step2: If MAC route from NVE1 is selected as the best, the GW advertise MAC1 route to NVE2 with a MAC mobility extended community, that carrying the increased seq number. Step3: The NVE2 receives the MAC1 route with MAC mobility extended community, and will select the MAC1 from the GW as the best, and withdraw the MAC1 originally sent to the GW. Step4: The traffic from user will re-triggers NVE2 to learn the local MAC1, which resulting in migration, and the NVE2 will advertise MAC1 route with MAC mobility extended community that carrying the seq + 1. Step5: When the GW receives the MAC1 route with MAC mobility extended community that carrying seq + 1, the GW will select the MAC1 from NVE2 as best, and send MAC1 route with seq + 1 to NVE1. Step6: After receiving the MAC1 route with MAC mobility extended community that carrying seq + 1, the NVE1 will select the MAC1 from the GW as the best, and withdraw the MAC1 originally sent to the GW. 2. The other scenario: Step1: When the GW receives MAC routes that have the same prefix, rather than different next hop and different ESI, the following conclusion can be drawn, which the MAC has been migrated. At the same time, the GW only send UMR route. Step2: If MAC route from NVE2 is selected as the best, the GW advertise MAC1 route to NVE1 with a MAC mobility extended community, that carrying the increased seq number. Step3: After receiving the MAC1 route with MAC mobility extended community that carrying seq + 1, the NVE1 will select the MAC1 from the GW as the best, and withdraw the MAC1 originally sent to the GW.

In addition, the draft also consider to the E-tree function in the UMR solution. The procedures would be detailed in a future revision.

TBD