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Feature Description - VPN 01

NE05E and NE08E V300R003C10SPC500

This is NE05E and NE08E V300R003C10SPC500 Feature Description - VPN
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EVPN Multi-Homing Technology

EVPN Multi-Homing Technology

Related Concepts

  • Designated forwarder (DF) election

    On the network shown in Figure 10-9, CE1 is dual-homed to PE1 and PE2, and CE2 sends BUM traffic to PE1 and PE2. In this scenario, CE1 receives the same copy of traffic from both PE1 and PE2, wasting network resources. To solve this problem, EVPN allows one PE to be elected to forward BUM traffic. The elected PE is referred to as the DF. If PE1 is elected, it becomes the primary DF, with PE2 functioning as the backup DF. The primary DF forwards BUM traffic from CE2 to CE1.

    If a PE interface connecting to a CE is Down, the PE functions as a backup DF. If a PE interface connecting to a CE is Up, the PE and other PEs with Up interfaces elect a primary DF using the following procedure:
    1. The PEs establish BGP EVPN peer relationships with each other and then exchange Ethernet segment routes.

    2. Upon receipt of the Ethernet segment routes, each PE generates a multi-homing PE list based on the ESIs carried in Ethernet segment routes. Each multi-homing PE list contains information about all PEs connecting to the same CE.

    3. Each PE then sequences the PEs in each multi-homing PE list based on the source IP addresses carried in Ethernet segment routes. The PEs are numbered from 0.

    4. If interface-based DF election is enabled, the PE with the smallest source IP address is elected to be the primary DF. If VLAN-based DF election is enabled, the PE with a specific sequence number is elected to be the primary DF. The sequence number is calculated using the following expression formula: (V mod N) = i, in which i indicates a PE's sequence number, N indicates the number of PEs to which a CE is multi-homed, and V indicates the VLAN ID over an Ethernet segment.

      NOTE:

      In a VLAN-aware bundle scenario, an Ethernet segment may have multiple VLANs configured. In this case, the smallest VLAN ID is used as the V value.

    Figure 10-9 DF election networking

  • Split horizon

    On the network shown in Figure 10-10, CE1 is dual-homed to PE1 and PE2 and has load balancing enabled. If PE1 and PE2 have established a BGP EVPN peer relationship with each other, after PE1 receives BUM traffic from CE1, PE1 forwards the BUM traffic to PE2. If PE2 forwards BUM traffic to CE1, a loop will occur. To prevent this problem, EVPN uses split horizon. After PE1 forwards the BUM traffic to PE2, PE2 checks the EVPN ESI label carried in the traffic. If the ESI carried in the label equals the ESI for the link between PE2 and CE1, PE2 does not forward the traffic to CE1, preventing a loop.

    Figure 10-10 Split horizon networking

  • Redundancy mode and aliasing

    If a CE is multi-homed to several PEs, a redundancy mode can be configured to specify the redundancy mode of PEs connecting to the same CE. The redundancy mode determines whether load balancing is implemented for unicast traffic in CE multi-homing scenarios. On the network shown in Figure 10-11, the transmission mode of unicast traffic sent by PE3 to CE1 varies according to the redundancy modes configured on PE1 and PE2.
    • If PE1 and PE2 are both configured to work in All-Active mode, after PE1 and PE2 send Ethernet auto-discovery route carrying the redundancy mode to PE3, PE3 sends unicast traffic destined for CE1 to both PE1 and PE2 in load balancing mode.

    • If either PE1 or PE2 or both PE1 and PE2 are configured to work in Single-Active mode, after PE1 and PE2 send Ethernet auto-discovery route carrying the redundancy mode to PE3, PE3 uses the optimal received route as the primary route and the second optimal received route as the backup route to implement FRR.

    EVPN also supports aliasing, which is the ability of a PE to signal that it has reachability to an EVPN instance on a given Ethernet segment even when it has learned no MAC addresses from that Ethernet segment. In the case where a CE is multi-homed to several PEs, it is possible that only a single PE learns a set of the MAC addresses associated with traffic transmitted by the CE. Aliasing enables remote PEs to learn the reachability of CE-side MAC addresses based on the ESIs carried in Ethernet auto-discovery route received from multi-homing PEs. On the network shown in Figure 10-11, only PE1 sends MAC/IP advertisement routes that carry CE-side MAC addresses to PE3, but PE3 can learn from Ethernet auto-discovery route that PE2 is also reachable to CE1. As a result, PE3 load-balances traffic destined for CE1 between PE1 and PE2.

    Figure 10-11 Redundancy mode and aliasing networking

  • Fast route convergence

    On the network shown in Figure 10-12, if the link between CE1 and PE1 fails, PE1 advertises an Ethernet auto-discovery route to PE3, informing PE3 that PE1 has become unreachable to Site 1. Upon receipt of the route, PE3 withdraws the corresponding routes and sends traffic to Site 1 only through PE2, implementing fast route convergence.

    Figure 10-12 Fast route convergence networking

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Updated: 2019-01-14

Document ID: EDOC1100058940

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