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NE20E-S V800R010C10SPC500 Feature Description - VPN 01

This is NE20E-S V800R010C10SPC500 Feature Description - VPN
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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 Seamless MPLS Fundamentals

EVPN Seamless MPLS Fundamentals

Seamless MPLS achieves end-to-end service transmission along an LSP traversing the access, aggregation, and core layers. Therefore, service traffic can be transmitted between any two points on an LSP. The seamless MPLS network architecture maximizes service scalability using the following functions:
  • Allows access nodes to signal all services to an LSP.
  • Uses the same transport layer convergence technology to switch all services to backup paths in case of network-side faults, ensuring proper service transmission.

Background

The use of MPLS networks increases requirements for service scalability of network architecture. Different MANs of a service provider or collaborative backbone networks of different service providers often span multiple ASs.

Implementation

Through seamless MPLS networking, all services (support inter-AS Option C) are signaled to an LSP only by access nodes, and all network-side faults are rectified using the same transport layer convergence technology, which does not affect service transmission.

Usage Scenario

Seamless MPLS supports the following networking solutions:

  • Intra-AS seamless MPLS: The access, aggregation, and core layers are deployed within a single AS. This solution mainly applies to mobile bearer networks.
  • Inter-AS seamless MPLS: The access and aggregation layers are deployed within a single AS, whereas the core layer in another AS. This solution mainly applies to enterprise services.

EVPN Intra-AS Seamless MPLS

Table 12-1 EVPN intra-AS seamless MPLS networking

Network Deployment

Description

Control plane

Deploy routing protocols.

In Figure 12-13, routing protocols are deployed on devices as follows:
  • An IGP (IS-IS or OSPF) is enabled on devices at the access, aggregation, and core layers to establish connectivity within the AS.

  • An IBGP peer relationship is established between each of the following pairs of devices:
    • CSG and AGG
    • AGG and core ABR
    • Core ABR and MASG

    An AGG and core ABR are configured as route reflectors (RRs) so that a CSG and MASG can obtain routes destined for each other's loopback address.

  • The next hop addresses in BGP routes are set on the AGG and core ABR to the devices' own addresses to prevent advertising unnecessary IGP area-specific public routes.

Figure 12-13 Routing protocol deployment for intra-AS seamless MPLS networking

Deploy tunnels.

In Figure 12-14, tunnels are deployed as follows:
  • A public network tunnel is established using LDP, TE, or LDP over TE in each IGP area.

  • An IBGP peer relationship is established between each of the following pairs of devices:
    • CSG and AGG
    • AGG and core ABR
    • Core ABR and MASG

    These devices are enabled to advertise labeled routes and assign labels to BGP routes that match a specified routing policy. After the devices exchange labeled BGP routes, an end-to-end BGP LSP is established between the CSG and MASG.

Figure 12-14 Tunnel deployment for intra-AS seamless MPLS networking

Forwarding plane

Figure 12-15 illustrates the forwarding plane of intra-AS seamless MPLS networking. Seamless MPLS is mainly used to transmit EVPN packets. The following example demonstrates how EVPN packets, including labels and data, are transmitted from a CSG to an MASG along the path CSG1->AGG1->core ABR1->MASG1.
  1. The CSG pushes a BGP LSP label and an MPLS tunnel label in sequence into each EVPN packet and forwards the packets to the AGG.

  2. Upon receipt, the AGG removes the access-layer MPLS tunnel labels from the packets and swaps the existing BGP LSP labels for new labels. The AGG then pushes an aggregation-layer MPLS tunnel label into each packet and proceeds to forward the packets to the core ABR. If the penultimate hop popping (PHP) function is enabled on the AGG, the CSG has removed the MPLS tunnel labels from the packets, and therefore, the AGG receives packets without MPLS tunnel labels.

  3. Upon receipt, the core ABR removes aggregation-layer MPLS tunnel labels from the EVPN packets and swaps the existing BGP LSP labels for new labels. The AGG pushes a core-layer MPLS tunnel label to each packet and forwards the packets to the MASG.

  4. Upon receipt, the MASG removes MPLS tunnel labels and BGP LSP labels from the EVPN packets. If the PHP function is enabled on the MASG, the core ABR has removed the core-layer MPLS tunnel labels from the packets, and therefore, the MASG receives packets without MPLS tunnel labels. The EVPN packet transmission along the intra-AS seamless MPLS LSP is complete.

Figure 12-15 Forwarding plane for intra-AS seamless MPLS networking

EVPN Inter-AS Seamless MPLS

Table 12-2 EVPN inter-AS seamless MPLS networking

Network Deployment

Description

Control plane

Deploy routing protocols.

In Figure 12-16, routing protocols are deployed on devices as follows:
  • An IGP (IS-IS or OSPF) is enabled on devices at the access, aggregation, and core layers to establish connectivity within the AS.

  • A BGP peer relationship is established between each of the following pairs of devices:
    • CSG and AGG
    • AGG and AGG ASBR
    • AGG ASBR and core ASBR
    • Core ASBR and MASG
    An EBGP peer relationship between an AGG ASBR and a core ASBR is established, and IBGP peer relationships between other devices are established.
  • The AGG is configured as an RR so that IBGP peers can exchange BGP routes, and the CSG and MASG can obtain BGP routes destined for each other's loopback addresses.

  • If the AGG ASBR and core ASBR are indirectly connected, an IGP neighbor relationship between them must be established to implement connectivity between ASs.

Figure 12-16 Routing protocol deployment for inter-AS seamless MPLS networking

Deploy tunnels.

In Figure 12-17, tunnels are deployed as follows:
  • A public network tunnel is established using LDP, TE, or LDP over TE in each IGP area. An LDP LSP or a TE LSP is established if more than one hop exists between the AGG ASBR and core ASBR.

  • The CSG, AGG, AGG ASBR, and core ASBR are enabled to advertise labeled routes and assign labels to BGP routes that match a specified routing policy. After the devices exchange labeled BGP routes, a BGP LSP is established between the CSG and core ASBR.

  • Tunnel deployment in the core area is as follows:
    • A BGP LSP between the core ASBR and MASG is established. This BGP LSP and the BGP LSP between the CSG and core ASBR are combined into an end-to-end BGP LSP. The route to the MASG's loopback address is imported into the BGP routing table and advertised to the core ASBR using the IBGP peer relationship. The core ASBR assigns a label to the route and advertises the labeled route to the AGG ASBR.

    • No BGP LSP is established between the core ASBR and MASG. The core ASBR runs an IGP to learn the route destined for the MASG's loopback address and imports the route to the routing table. The core ASBR assigns a BGP label to the route and associates the route with an intra-AS LSP. The BGP LSP between the CSG and core ASBR and the MPLS LSP in the core area are combined into an end-to-end tunnel.

Figure 12-17 Tunnel deployment for inter-AS seamless MPLS networking

Forwarding plane

Figure 12-18 illustrates the forwarding plane of the inter-AS seamless MPLS networking with a core-layer BGP LSP established. Seamless MPLS is mainly used to transmit EVPN packets. The following example demonstrates how EVPN packets, including labels and data, are transmitted from a CSG to an MASG along the path CSG1->AGG1->AGG ASBR1->core ASBR1->MASG1.
  1. The CSG pushes a BGP LSP label and an MPLS tunnel label in sequence into each EVPN packet and forwards the packets to the AGG.

  2. Upon receipt, the AGG removes the access-layer MPLS tunnel labels from the packets and swaps the existing BGP LSP labels for new labels. The AGG then pushes an aggregation-layer MPLS tunnel label into each packet and proceeds to forward the packets to the AGG ASBR. If the PHP function is enabled on the AGG, the CSG has removed the MPLS tunnel labels from the packets, and therefore, the AGG receives packets without MPLS tunnel labels.

  3. Upon receipt, the AGG ASBR removes the MPLS tunnel labels from the EVPN packets and swaps the existing BGP LSP label for a new label in each packet. It then forwards the packets to the core ASBR. If the PHP function is enabled on the AGG ASBR, the AGG has removed the MPLS tunnel labels from the packets, and therefore, the AGG ASBR receives packets without MPLS tunnel labels.

  4. Upon receipt, the core ASBR swaps a BGP LSP label for a new label and pushes a core-layer MPLS tunnel label into each packet. It then forwards the packets to the MASG.

  5. Upon receipt, the MASG removes MPLS tunnel labels, BGP LSP labels, and VPN labels from the packets. If the PHP function is enabled on the core ASBR, the core ASBR has removed the MPLS tunnel labels from the packets, and therefore, the MASG receives packets without MPLS tunnel labels.

    The EVPN packet transmission along the inter-AS seamless MPLS LSP is complete.

Figure 12-18 Forwarding plane for the inter-AS seamless MPLS networking with a BGP LSP established in the core area

Figure 12-19 illustrates the forwarding plane for the inter-AS seamless MPLS networking without a BGP LSP established in the core area. The process of transmitting EVPN packets on this network is similar to that on a network with a BGP LSP established. The difference is that without a BGP LSP in the core area, the core ASBR removes BGP labels from packets and pushes MPLS tunnel labels into these packets.

Figure 12-19 Forwarding plane for the inter-AS seamless MPLS networking without a BGP LSP established in the core area

Reliability

Seamless MPLS network reliability can be improved using various functions. If a network fault occurs, a device immediately detects the fault and switch traffic to a standby link.

The following examples demonstrate reliability functions on an inter-AS seamless MPLS network.

  • A fault occurs on a link between a CSG and an AGG.

    On the inter-AS seamless MPLS network shown in Figure 12-20, the active link along the primary path between CSG1 and AGG1 fails. After BFD for LDP LSP or BFD for CR-LSP detects the fault, the BFD module uses LDP FRR, TE hot-standby, or BGP FRR to switch traffic from the primary path to the backup path.

    Figure 12-20 Traffic protection triggered by a fault on the link between the CSG and AGG on the inter-AS seamless MPLS network
  • A fault occurs on an AGG.

    On the inter-AS seamless MPLS network shown in Figure 12-21, BGP auto FRR is configured on CSGs and AGG ASBRs to protect traffic on the BGP LSP between CSG1 and MASG1. If BFD for LDP or BFD for TE detects AGG1 failure, the BFD module instructs CSG1 to switch traffic from the primary path to the backup path.

    Figure 12-21 Traffic protection triggered by a fault on an AGG on the inter-AS seamless MPLS network
  • A fault occurs on the link between an AGG and an AGG ASBR.

    On the inter-AS seamless MPLS network shown in Figure 12-22, a fault occurs on the link between AGG1 and AGG ASBR1. After BFD for LDP LSP or BFD for CR-LSP detects the fault, the BFD module uses LDP FRR, TE hot-standby, or BGP FRR to switch traffic from the primary path to the backup path.

    Figure 12-22 Traffic protection triggered by a fault on the link between an AGG and an AGG ASBR on the inter-AS seamless MPLS network
  • A fault occurs on an AGG ASBR.

    On the inter-AS seamless MPLS network shown in Figure 12-23, BFD for LDP or BFD for TE is configured on AGG1, and BFD for interface is configured on core ASBR1. If AGG ASBR1 fails, the BFD modules on AGG1 and core ASBR1 detect the fault and trigger BGP auto FRR. BGP auto FRR switches both upstream and downstream traffic from the primary path to backup paths.

    Figure 12-23 Traffic protection triggered by a fault on an AGG ASBR on the inter-AS seamless MPLS network
  • A fault occurs on the link between an AGG ASBR and a core ASBR.

    On the inter-AS seamless MPLS network shown in Figure 12-24, BFD for interface is configured on AGG ASBR1 and core ASBR1. If the BFD module detects a fault on the link between AGG ASBR1 and core ASBR1, the BFD module triggers BGP Auto FRR. BGP auto FRR switches both upstream and downstream traffic from the primary path to backup paths.

    Figure 12-24 Traffic protection triggered by a fault on the link between an AGG ASBR and a core ASBR on the inter-AS seamless MPLS network
  • A fault occurs on a core ASBR.

    On the inter-AS seamless MPLS network shown in Figure 12-25, BFD for interface and BGP auto FRR are configured on AGG ASBR1. BGP auto FRR and BFD for LDP (or for TE) are configured on MASGs to protect traffic on the BGP LSP between CSG1 and MASG1. If the BFD module detects a fault on core ASBR1, it instructs AGG ASBR1 to switch both upstream and downstream traffic from the primary path to backup paths.

    Figure 12-25 Traffic protection triggered by a fault on a core ASBR on the inter-AS seamless MPLS network
  • A link fault occurs in the core area.

    On the inter-AS seamless MPLS network shown in Figure 12-26, BFD for LDP or BFD for TE is configured on core ASBR1. If the BFD module detects a fault on the link between core ASBR1 and MASG1, it triggers the LDP FRR, TE hot-standby, or BGP FRR function. The reliability function switches both upstream and downstream traffic from the primary path to the backup path.

    Figure 12-26 Traffic protection from a link fault in a core area on the inter-AS seamless MPLS network
  • A fault occurs on an MASG.

    On the inter-AS seamless MPLS network shown in Figure 12-27, BFD for BGP tunnel is configured on CSG1. BFD for BGP tunnel is implemented in compliance with relevant standards "Bidirectional Forwarding Detection (BFD) for MPLS Label Switched Paths (LSPs)." BFD for BGP tunnel monitors end-to-end BGP LSPs, including a BGP LSP connected to an LDP LSP. If MASG1 functioning as a PE fails, BFD for BGP LSP can rapidly detect the fault and trigger VPN FRR switching so that both upstream and downstream traffic are switched from the primary path to the backup path.

    Figure 12-27 Traffic protection triggered by a fault on an MASG on the inter-AS seamless MPLS network
  • An access-side link fails.

    On the inter-AS seamless MPLS network shown in Figure 12-28, if an E-Trunk in Single-Active redundancy mode detects the link failure, and the E-Trunk switches traffic from the primary path to the backup path and disables interface blocking on the link between CE1 and PE2. Then upstream traffic on CE1 is forwarded to PE2. For BUM traffic on the network side, PE1 sends a Per ES-AD-withdraw message to PE2, and PE2 is elected as the primary DF to forward BUM traffic. For unicast traffic, PE3 receives a MAC route advertised by PE2 and forwards the traffic to PE2.

    If an E-Trunk in Active-Active redundancy mode detects the link failure, PE1 sends a Per ES-AD route-withdraw message to PE3, and PE3 forwards unicast traffic to PE2.

    Figure 12-28 Traffic protection triggered by an access-side link fault in a core area on the inter-AS seamless MPLS network
  • A PE on the access side fails.

    If PE1 fails, the reliability implementation is similar to that in the access-side link failure scenario. The other PEs detect PE1 failure and switch traffic from the primary path to backup paths without withdrawing routes.

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Updated: 2019-01-03

Document ID: EDOC1100055135

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