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NE40E V800R010C00 Feature Description - VPN 01

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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
EVPN Principles

EVPN Principles

EVPN Networking

An EVPN has a similar network structure to a BGP/MPLS IP VPN. In EVPN networking, CEs at each site connect to PEs on the ISP backbone network. These PEs have EVPN instances configured and establish BGP EVPN peer relationships and LDP tunnels with each other. Unlike a BGP/MPLS IP VPN, an EVPN has its sites on Layer 2 networks. Therefore, the PEs learn MAC addresses but not IP routes from the CEs, and then advertise the learned MAC addresses to other sites using EVPN routes.

In EVPN networking, a CE can be single-homed to one PE or multi-homed to several PEs. On the network shown in Figure 12-1, CE1, CE2, and CE4 use the single-homing mode, whereas CE3 uses the multi-homing mode. Load balancing can be implemented in CE multi-homing networking.

EVPN defines Ethernet segment identifiers (ESIs) to identify links between PEs and CEs. Links connecting multiple PEs to the same CE have the same ESI, and links connecting multiple PEs to different CEs have different ESIs. PEs exchange routes that carry ESIs, so that a PE can discover other PEs connecting to the same CE as itself.

Figure 12-1  EVPN networking

EVPN Routes

To enable sites to learn MAC addresses from each other, EVPN defines a new type of BGP network layer reachability information (NLRI), called the EVPN NLRI. The EVPN NLRI defines four types of EVPN routes:
  • Ethernet auto-discovery route: carries the reachability of the local PE to the MAC addresses of its connected sites. PEs advertise Ethernet auto-discovery routes after establishing a BGP EVPN peer relationship. Ethernet auto-discovery routes are used in Fast route convergence, Redundancy mode and aliasing, and Split horizon. Figure 12-2 shows the format of an EVPN NLRI specific to the Ethernet auto-discovery route.

    Figure 12-2  EVPN NLRI specific to the Ethernet auto-discovery route

    The description of each field is as follows:
    • Route Distinguisher: an 8-byte field. The value can be either the RD value of an EVPN instance or a combination of the source IP address configured on a PE and :0, such as X.X.X.X:0.

    • Ethernet Segment Identifier: a 10-byte field that identifies links between PEs and CEs.

    • Ethernet Tag ID: a 4-byte field that is all 0s or Fs for Ethernet auto-discovery routes.

    • MPLS Label: a field that is all 0s or used as an MPLS label for EVPN unicast traffic to be forwarded in load balancing mode.

  • MAC advertisement route: carries EVPN instance RD, ESI, and label information on the local PE. For details, see Unicast MAC Address Transmission. Figure 12-3 shows the format of an EVPN NLRI specific to the MAC advertisement route.

    Figure 12-3  EVPN NLRI specific to the MAC advertisement route

    The description of each field is as follows:
    • Route Distinguisher: an 8-byte field representing the RD value of an EVPN instance.

    • Ethernet Segment Identifier: a 10-byte field that identifies links between PEs and CEs.

    • Ethernet Tag ID: a 4-byte field representing the actual VLAN ID configured on a PE.

    • MAC Address Length: a 1-byte field representing the length of the MAC address advertised by the route.

    • MAC Address: a 6-byte field representing the MAC address advertised by the route.

    • MAC Address Length: a field representing the mask length of the host IP address advertised by the route.

    • IP Address: a field representing the host IP address advertised by the route.

    • MPLS Label1: a field representing the label used for Layer 2 service traffic forwarding.

    • MPLS Label2: a field representing the label used for Layer 3 service traffic forwarding.

  • Inclusive multicast route: carries EVPN instance RD and RT information and source IP address on the local PE. The source IP address is usually the loopback interface address of the local PE. PEs transmit inclusive multicast routes after establishing a BGP EVPN peer relationship. EVPN involves BUM traffic. A PE forwards the BUM traffic that it receives to other PEs in P2MP mode. BUM traffic can traverse inclusive multicast routes. For details, see BUM Packet Transmission. Figure 12-4 shows the format of an EVPN NLRI specific to the inclusive multicast route.

    Figure 12-4  EVPN NLRI specific to the inclusive multicast route

    The description of each field is as follows:
    • Route Distinguisher: an 8-byte field representing the RD value of an EVPN instance.

    • Ethernet Tag ID: a 4-byte field that is all 0s for inclusive multicast routes.

    • IP Address Length: a 1-byte field representing the length of the source IP address configured on the local PE.

    • Originating Router's IP Address: a 4-byte or 16-byte field representing the source IP address configured on the local PE.

  • Ethernet segment route: carries the EVPN instance RD and ESI information and source IP address on the local PE. PEs connecting to the same CE use Ethernet segment routes to discover each other. This type of route is used in Designated forwarder election. Figure 12-5 shows the format of an EVPN NLRI specific to the Ethernet segment route.

    Figure 12-5  EVPN NLRI specific to the Ethernet segment route

    The description of each field is as follows:
    • Route Distinguisher: an 8-byte field representing a combination of the source IP address on the local PE and :0, such as X.X.X.X:0.

    • Ethernet Segment Identifier: a 10-byte field that identifies links between PEs and CEs.

    • IP Address Length: a 1-byte field representing the length of the source IP address configured on the local PE.

    • Originating Router's IP Address: a 4-byte or 16-byte field representing the source IP address configured on the local PE.

Unicast MAC Address Advertisement

On the network shown in Figure 12-6, unicast MAC addresses are advertised as follows:
  1. CE1 sends an ARP Request message or a gratuitous ARP message to advertise its MAC address (MAC A) and IP address to CE2. After the ARP Request message or gratuitous ARP message arrives at PE1, PE1 generates a MAC advertisement route based on MAC A.

  2. CE2 receives the ARP Request message or gratuitous ARP message from CE1 and responds with an ARP Reply message or a gratuitous ARP message carrying CE2's MAC address (MAC B) and IP address. After the ARP Reply message or gratuitous ARP message arrives at PE2, PE2 generates a MAC advertisement route based on MAC B.

  3. PE1 and PE2 exchange MAC advertisement route that carry MAC addresses, next hops, and EVPN instance extended community attributes (such as RTs).

  4. PE1 and PE2 construct EVPN instance forwarding entries based on the RTs carried in received MAC advertisement route.

Figure 12-6  Unicast MAC address advertisement networking

Unicast Packet Transmission

After a PE connecting to a site has learned the MAC addresses of other sites and established public network tunnels, the PE can send unicast packets to other sites. On the network shown in Figure 12-7, unicast packets are transmitted as follows:
  1. CE2 forwards unicast packets to PE2 at Layer 2.

  2. Upon receipt of the unicast packets, PE2 encapsulates an EVPN label, a public network LDP LSP label, PE2's MAC address, and PE1's MAC address in sequence into the unicast packets. PE2 then forwards the encapsulated unicast packets to PE1.

  3. PE1 decapsulates the received unicast packets and sends the unicast packets to the sites of the EVPN identified by the EVPN label carried in the packets.

Figure 12-7  Unicast packet transmission networking

BUM Packet Transmission

After two PEs establish a BGP EVPN peer relationship, they exchange inclusive multicast routes. A PE can discover PEs that belong to the same EVPN instance as itself based on RTs carried in the inclusive multicast routes it receives. The RTs identify the reachability information of these PEs. This PE then automatically establishes LDP tunnels with these PEs. BUM packets can then traverse these LDP tunnels. On the network shown in Figure 12-8, BUM packets are transmitted as follows:
  1. CE1 sends BUM packets to PE1.

  2. Upon receipt of the BUM packets, PE1 forwards them to PE2 and PE3 that belong to the same EVPN. Specifically, PE1 replicates the received BUM packets and encapsulates the EVPN BUM label, public network LDP LSP label, PE1's MAC address, and P's MAC address in sequence into these packets before sending them to PE2 and PE3.

  3. Upon receipt of the BUM packets, PE2 and PE3 decapsulate the BUM packets and send the BUM packets to the sites of the EVPN identified by the EVPN BUM label carried in the packets.

NOTE:

In the case where a CE is dual-homed to two PEs, an EVPN ESI label will be encapsulated into the BUM packets exchanged between the two PEs to prevent loops.

Figure 12-8  BUM packet transmission networking

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Updated: 2018-07-04

Document ID: EDOC1100027166

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