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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).
Carrier's Carrier

Carrier's Carrier

Background

A customer of an SP providing the BGP/MPLS IP VPN service may also be an SP. In this case, the SP providing the BGP/MPLS IP VPN service is called the provider carrier or the first carrier and the customer is called the customer carrier or the second carrier, as shown in Figure 7-19. This networking model is called carrier's carrier. In this model, the customer carrier is a VPN user of the provider carrier.

Figure 7-19 Networking of carrier's carrier

Related Concepts

  • Internal routes and external routes

    To ensure good expansibility, the customer carrier uses an operation mode similar to that of a stub VPN. In other words, the provider carrier CE (also calledthe customer carrier PE) advertises only internal routes, instead of the internal and external routes of the customer carrier to the provider carrier PE. In this section, the internal and external routes of the customer carrier are called internal and external routes for short.

    The differences between internal and external routes are as follows:

    • The routes to the backbone network of the customer carrier are called internal routes. The routes to VPNs of the customer carrier are called external routes.

    • Provider carrier PEs exchange internal routes using BGP. The external routes are exchanged using BGP between customer carrier PEs. The external routes are not advertised to provider carrier PEs.

    • The VPN-IPv4 routes of the customer carrier are regarded as external routes. The provider carrier PEs import only internal routes and not external routes to their VRFs, reducing the number of routes that need to be maintained on the provider carrier network. The customer carrier network has to maintain both internal and external routes.

    NOTE:

    A provider carrier CE is a device through which the customer carrier network accesses the provider carrier network. A user CE is a device through which a user accesses the customer carrier network.

  • Classification of carrier scenarios

    Compared with a basic BGP/MPLS IP VPN, the access of provider carrier CEs to provider carrier PEs is the key to the carrier's carrier model. A customer carrier can be a common SP or a BGP/MPLS IP VPN SP.

    • If a customer carrier is a common SP, MPLS does not need to be configured on customer carrier PEs. Customer carrier PEs communicate with provider carrier PEs using an IGP. Customer carrier PEs exchange external routes with each other over BGP sessions, as shown in Figure 7-20.

      Figure 7-20 Customer carrier serving as a common SP

      Table 7-2 Comparison between networking modes for customer carriers serving as common SPs and those serving as BGP/MPLS IP VPN SPs

      Location of Provider Carrier's Backbone Network and Customer Carrier Network

      Characteristics

      In the same AS

      Provider carrier PEs and CEs exchange routes using the IGP and LDP. Provider carrier CEs exchange external routes between each other using BGP.

      In different ASs

      Provider carrier PEs and CEs exchange labeled VPN-IPv4 routes using EBGP. Provider carrier CEs exchange external routes between each other using BGP.

    • If a customer carrier is a BGP/MPLS IP VPN SP, customer carrier PEs must be configured with MPLS. Customer carrier PEs communicate with provider carrier CEs using the IGP and LDP. Customer carrier PEs exchange external routes between each other using MP-BGP, as shown in Figure 7-21.

      Figure 7-21 Customer carrier serving as a BGP/MPLS IP VPN SP

      Table 7-3 Comparison between networking modes for customer carriers serving as BGP/MPLS IP VPN SPs

      Location of Provider Carrier's Backbone Network and Customer Carrier Network

      Characteristics

      In the same AS

      Provider carrier PEs and CEs exchange routes and labels using the IGP and LDP. When entering the customer carrier network, VPN packets must be double-tagged.

      In different ASs

      Provider carrier PEs and CEs exchange routes and labels using MP-EBGP. When entering the customer carrier network, VPN packets must be triple-tagged.

Route Exchanging in the Scenario in Which the Customer Carrier Is a Common SP (Same AS)

Figure 7-22 shows route exchanging in the scenario in which a customer carrier is a common SP and the provider carrier's backbone network and the customer carrier network are in the same AS. D represents the destination address, N the next hop, and L the label.

Figure 7-22 Route exchanging in the scenario in which the customer carrier is a common SP (same AS)

The following uses the advertisement of an Internet route destined for 10.1.1.1/32 from CE4 to ASBR1 as an example to show Internet route exchange inside the customer carrier network.

  1. CE2 advertises an internal route (use the route destined for CE2 as an example) to PE2 using the IGP and also assigns label L0 to the route using LDP.

  2. PE2 assigns label L1 to the route using MP-IBGP and advertises the route to PE1. Previously, PE2 has advertised its routes to PE1 using the IGP running on the provider carrier's backbone network and has assigned label L' to the routes destined for itself. In this manner, a public network LSP is established between PE2 and PE1.

  3. PE1 assigns label L2 to the route using LDP and advertises the label and route to CE1 using the IGP running between PE1 and CE1.

  4. CE1 advertises the route to ASBR1 using the IGP running on the customer carrier network.

  5. After the routes of the VPN where CE1 and ASBR1 reside are advertised to CE2, an IBGP connection is set up between CE1 and CE2.

  6. ASBR2 advertises the external route destined for 10.1.1.1/32 and learned from CE4 to CE2 using the IGP running in the AS. Previously, ASBR2 has set the next hop of this route as CE4.

  7. CE2 imports this external route to BGP and advertises this route to CE1 using IBGP.

  8. Upon receipt, CE1 sets the next hop of this route as CE2, and advertises the route to ASBR1 using the IGP running on the customer carrier network. Here, the customer carrier networks are in the same AS, and CE1 needs to be configured as an RP between CE2 and ASBR1.

The process of advertising the routes of the VPN where ASBR1 and CE1 reside to CE2 and ASBR2 is similar to this process and therefore is not described.

Route Exchanging in the Scenario in Which the Customer Carrier Is a Common SP (Different ASs)

Figure 7-23 shows route exchanging in the scenario in which the customer carrier is a common SP and the customer carrier network and the provider carrier's backbone network are in different ASs. D represents the destination address of a route, N the next hop, and L the label.

Figure 7-23 Route exchanging in the scenario in which the customer carrier is a common SP (different ASs)

The following uses the advertisement of an Internet route destined for 10.1.1.1/32 from CE4 to ASBR1 as an example to show Internet route exchange inside the customer carrier network.

  1. CE2 advertises a route destined for itself to PE2 using EBGP running between CE2 and PE2. Meanwhile, CE2 assigns label L0 to this route.

  2. PE2 assigns label L1 to the route using MP-IBGP and advertises the route to PE1.

    Previously, PE2 has advertised its routes to PE1 using the IGP run on the provider carrier's backbone network and has assigned label L' to the routes destined for itself. A public network LSP has been established between PE2 and PE1.

  3. PE1 assigns label L2 to the route using MP-IBGP and advertises the route to CE1.

  4. CE1 advertises the route to ASBR1 using the IGP running on the customer carrier network.

  5. After the routes of CE1 are advertised to CE2, an EBGP connection is established between CE1 and CE2.

  6. ASBR2 advertises the external route destined for 10.1.1.1/32 to CE4 using the IGP running on the customer carrier network.

  7. CE2 imports the route to BGP and advertises this route to CE1 using EBGP.

  8. Upon receipt, CE1 sets the next hop of this route as CE2, and advertises the route to ASBR1 using the IGP running on the customer carrier network.

The process of advertising the routes of the AS where ASBR1 and CE1 reside to CE2 and ASBR2 is similar and therefore is not described.

Packet Forwarding in the Scenario in Which the Customer Carrier Is a Common SP

If the customer is a common SP, packet forwarding is the same no matter whether the provider carrier's backbone network and customer carrier network is in the same AS or different ASs. Figure 7-24 shows user packet transmission over carrier networks if the customer carrier is a common SP. L represents the label assigned by the provider carrier network using MP-BGP, and L' represents the public network label used on the provider carrier network.

Figure 7-24 Packet forwarding in the scenario in which the customer carrier is a common SP

The following uses forwarding of a packet destined for 10.1.1.1/32 from ASBR1 to CE4 as an example to describe packet transmission over carrier networks:

  1. ASBR1 transparently transmits the packet to CE1 based on IP forwarding.

  2. CE1 adds label L2 to the packet and forwards this packet to PE1.

  3. PE1 replaces label L2 with label L1 and adds label L' to the packet. PE1 then forwards the packet to PE2 over the public network LSP.

  4. PE2 replaces L1 with L0 and forwards the packet to CE2.

  5. CE2 removes label L' and forwards the packet to ASBR2 based on IP forwarding.

  6. ASBR2 advertises the packet to CE4.

Route Exchanging in the Scenario in Which the Customer Carrier Is a BGP/MPLS IP VPN SP (Same AS)

Figure 7-25 shows route exchanging in the scenario in which the customer carrier is a BGP/MPLS IP VPN SP and the provider carrier's backbone network are in the same AS as the customer carrier network. D represents the destination address of a route, N the next hop, and L the label.

Figure 7-25 Route exchanging in the scenario in which the customer carrier is a BGP/MPLS IP VPN SP (same AS)

The following uses the advertisement of a VPN route destined for 10.1.1.1/32 from PE4 to PE3 as an example to describe VPN route exchange inside the customer carrier network.

  1. PE4 advertises a route destined for itself to CE2 using the IGP running on the customer carrier network. Meanwhile, PE4 assigns label L''1 to the IGP next hop and establishes a public network LSP with CE2.

  2. CE2 advertises the route to PE2 using the IGP running between CE2 and PE2. Meanwhile, CE2 assigns label L1 to the route using LDP.

  3. PE2 assigns label L2 to the route and advertises the route to PE1 using MP-IBGP. Previously, PE2 has advertised its routes to PE1 using the IGP running on the provider carrier's backbone network and assigned label L' to the routes destined for itself. A public network LSP has been established between PE2 and PE1.

  4. PE1 assigns label L3 to the route using LDP running between PE1 and CE1 and advertises the route to CE1.

  5. CE1 advertises the route to PE3 using the IGP running on the customer carrier network.

    Previously, CE1 has advertised its routes to PE1 using the IGP running on the provider carrier's backbone network and assigned label L''2 to the routes destined for itself. A public network LSP has been established between CE1 and PE3.

  6. After the routes destined for PE3 are advertised to PE4, an MP-IBGP connection is established between PE3 and PE4.

  7. PE4 assigns VPN label I-L to the VPN route destined for 10.1.1.1/32 and advertises the route to PE3 using MP-IBGP.

    The advertisement of a VPN route from PE3 to PE4 is similar to that from PE4 to PE3 and therefore is not described here.

Packet Forwarding in the Scenario in Which the Customer Carrier Is a BGP/MPLS IP VPN SP (Same AS)

Figure 7-26 shows packet forwarding in the scenario in which the customer carrier is a BGP/MPLS IP VPN SP and the provider carrier's backbone network are in the same AS as the customer carrier network. I-L represents the VPN label assigned using MP-BGP. L' indicates the public network label used on the provider carrier network. L''1 and L''2 stand for public network labels used on the customer carrier network. L1, L2, and L3 represent labels assigned to packets destined for PE4.

Figure 7-26 Packet forwarding in the scenario in which the customer carrier is a BGP/MPLS IP VPN SP (same AS)

The following uses forwarding of a VPN packet destined for 10.1.1.1/32 from PE3 to CE4 as an example to describe packet transmission over carrier networks.

  1. After receiving a VPN packet destined for 10.1.1.1/32, PE3 adds the VPN label I-L to this packet and transparently transmits the packet to CE1 over the public network LSP on the customer carrier network.

    Before the packet arrives at CE1, the penultimate LSR removes the outer public network label of the packet.

  2. CE1 adds label L3 to the packet and forwards this packet to PE1.

  3. PE1 replaces label L3 with label L2 and adds label L' to the packet. PE1 then forwards the packet to PE2 over the public network LSP. Label L' is removed on the penultimate LSR of PE2.

  4. PE2 replaces label L2 with label L1 and forwards the packet to CE2.

  5. CE2 removes label L1, adds label L''1, and transparently forwards the packet to PE4 over the public network LSP on the customer carrier network.

    Before the packet arrives at PE4, the penultimate LSR removes label L''1.

  6. PE4 removes label I-L and forwards the packet to CE4 based on label I-L.

Route Exchanging in the Scenario in Which the Customer Carrier Is a BGP/MPLS IP VPN SP (Different ASs)

Figure 7-27 shows route exchanging in the scenario in which the customer carrier is a BGP/MPLS IP VPN SP and the customer carrier network and the provider carrier's backbone network are in different ASs. D represents the destination address of a route, N the next hop, and L the label.

Figure 7-27 Route exchanging in the scenario in which the customer carrier is a BGP/MPLS IP VPN SP (different ASs)

The following uses the advertisement of a VPN route destined for 10.1.1.1/32 from PE4 to PE3 as an example to describe VPN route exchange inside the customer carrier network.

  1. PE4 advertises a route destined for itself to CE2 using the IGP running on the customer carrier network. Meanwhile, PE4 assigns label L''1 to the IGP next hop and establishes a public network LSP with CE2.

  2. CE2 assigns label L1 to the route and advertises the route to PE2 using MP-EBGP.

  3. PE2 assigns label L2 to the route and advertises the route to PE1 using MP-IBGP.

    Previously, PE2 has advertised its routes to PE1 using the IGP running on the provider carrier's backbone network and assigned label L' to the routes destined for itself. A public network LSP has been established between PE2 and PE1.

  4. PE1 assigns label L3 to the route and advertises the route to CE1 using MP-EBGP.

  5. CE1 assigns label L4 to the route and advertises the route to PE3 using MP-IBGP.

    Previously, CE1 has advertised its routes to PE3 using the IGP running on the customer carrier's backbone network and assigned label L' to the routes destined for itself. A public network LSP has been established between CE1 and PE3.

  6. A BGP LSP is established between CE2 and PE3.

    After the routes of PE3 are advertised to PE4, an MP-EBGP connection is established between PE3 and PE4.

  7. PE4 assigns VPN label I-L to the VPN route destined for 10.1.1.1/32 and advertises the route to PE3 using MP-EBGP.

The advertisement of a VPN route from PE3 to PE4 is similar to that from PE4 to PE3 and therefore is not described here.

Packet Forwarding in the Scenario in Which the Customer Carrier Is a BGP/MPLS IP VPN SP (Different ASs)

Figure 7-28 shows packet forwarding in the scenario in which the customer carrier is a BGP/MPLS IP VPN SP and the customer carrier network and the provider carrier's backbone network are in different ASs. I-L represents the VPN label assigned using MP-BGP. L' indicates the public network label used on the provider carrier network. L''1 and L''2 stand for public network labels used on the customer carrier network. L1, L2, L3, and L4 represent labels assigned to packets destined for PE4.

Figure 7-28 Packet forwarding in the scenario in which the customer carrier is a BGP/MPLS IP VPN SP (different ASs)

The following uses forwarding of the VPN packet destined for 10.1.1.1/32 from PE3 to CE4 as an example to describe VPN packet forwarding over carrier networks.

  1. After receiving the VPN packet destined for 10.1.1.1/32, PE3 adds the VPN label I-L and BGP LSP label L4 to this packet and transparently forwards the packet to CE1 over the public network LSP on the customer carrier network.

    Before the packet arrives at CE1, the penultimate LSR removes the outer public network label of the packet.

  2. CE1 replaces L4 with L3 and forwards the packet to PE1.

  3. PE1 replaces label L3 with label L2, adds label L', and forwards the packet to PE2 over the public network LSP. Before the packet arrives at PE2, the penultimate LSR removes label L'.

  4. PE2 replaces label L2 with label L1 and forwards the packet to CE2.

  5. CE2 removes label L1, adds label L''1, and transparently forwards the packet to PE4 over the public network LSP on the customer carrier network.

    Before the packet arrives at PE4, the penultimate LSR removes label L''1.

  6. PE4 removes label I-L and forwards the packet to CE4 based on label I-L.

Benefits

The carrier's carrier model has the following advantages:

  • Part of the configuration, management, and maintenance work used to be carried out by the customer carrier can be undertaken by the provider carrier.

  • The customer carrier can flexibly plan addresses, as its addresses are independent of those of the customers and the provider carrier.

  • The provider carrier can provide VPN services for multiple customer carriers over a backbone network, and can provide Internet services at the same time. This increases the profits of the provider carrier.

  • The provider carrier manages and maintains VPN services of each customer carrier in the same manner instead of maintaining individual backbone networks for customer carriers. This simplifies the operation of the provider carrier.

The carrier's carrier model has the following disadvantages: As a strict symmetrical networking mode, only VPN users at the same network level can communicate with each other.

VPN users at the same network level need to directly exchange VPN routing information between each other. Therefore, these user devices must be routable. The user devices at the same network level must maintain all routing information of this network level. The PEs at the same network level need to directly exchange VPNv4 routes between each other.

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Updated: 2019-01-03

Document ID: EDOC1100055135

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