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NE40E V800R010C00 Feature Description - VPN 01

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BGP/MPLS IP VPN Label Distribution Modes

BGP/MPLS IP VPN Label Distribution Modes

Background

On a BGP/MPLS IP VPN, a private network label (MPLS label) is assigned for each VPN route by default. If a large number of VPN routes exist, MPLS label resources may be insufficient. Other label distribution modes can be used to save MPLS label resources. Table 7-5 compares the label distribution modes which are currently available.

Table 7-5  Comparison among label distribution modes

Label Distribution Mode

Description

Applicable Networking

Configuration Position

One label per instance

All the VPN routes from a VPN instance are assigned the same private network label.

All types of BGP/MPLS IP VPNs

Devices on which VPN instances are configured

One label per next hop

All the VPN routes with the same next hop and outgoing label are assigned the same private network label.

Application mode 1:

One-label-per-next-hop label distribution in the BGP-VPNv4/6 view mainly applies to the inter-AS VPN OptionB scenario.

Application mode 2:

One-label-per-next-hop label distribution in the VPN instance view applies to all BGP/MPLS IP VPN scenarios.

Application mode 1. ASBRs in the inter-AS VPN OptionB networking

Application mode 2. Devices where VPN instances are configured

Implementation

One Label per Instance

After one-label-per-instance label distribution is configured in the IPv4 or IPv6 address family of a VPN instance, all the VPN routes from the corresponding address family of the VPN instance share the same private network label. On the network shown in Figure 7-38, PE1 has two VPN instances: VPN1 and VPN2. If PE1 receives 10,000 VPN routes from VPN1 and VPN2, respectively, PE1 assigns 20,000 private network labels to these routes by default. After one-label-per-instance label distribution is configured, PE1 assigns only one label to the 10,000 VPN routes received from VPN1 and one label to the 10,000 VPN routes received from VPN2.

Figure 7-38  One label per instance

One label per next hop

By default, an ASBR or a PE assigns a private network label to each VPN route. You can also configure an ASBR or a PE to distribute labels based on next hops. After one-label-per-next-hop label distribution is configured on an ASBR or a PE, the ASBR or a PE re-advertises an MP-BGP Update packet to its peers. The MP-BGP Update packet carries VPNv4 routes and their labels that are re-assigned based on next hops. After a peer receives the MP-BGP Update packet, the peer updates its local label forwarding table and re-establishes LSPs. After the ASBR or a PE and its peers update their label forwarding tables, packets are forwarded based on the updated label forwarding tables.

Figure 7-39  One label per next hop

One-label-per-next-hop label distribution applies to the routes sent by a VPN instance to PE1 or the routes learned by an ASBR from its peers.

  • Application mode 1. As shown in Figure 7-39, two VPN instances named VPN1 and VPN2 are configured on PE1 in inter-AS VPN Option B mode. PE1 uses the one-label-per-instance label distribution mode. If one-label-per-next-hop label distribution is disabled on ASBR1, ASBR1 assigns 20,000 labels to the 20,000 VPN routes imported from CE1 and CE2 over PE1 before advertising these routes to ASRB2. If one-label-per-next-hop label distribution is enabled on ASBR1, ASBR1 only needs to assign one label to the VPN routes with the same next hop and outgoing label. Therefore, ASBR1 assigns only two labels to the 20,000 routes imported from CE1 and CE2 over PE1 before advertising these routes to ASRB2.

  • Application mode 2. As shown in Figure 7-39, In the inter-AS VPN Option B scenario, two VPN instances named VPN1 and VPN2 are configured on PE1. 10,000 VPN routes are imported to each of CE1 and CE2 corresponding to VPN1 and VPN2. If one-label-per-next-hop label distribution is disabled on PE1, PE1 assigns 20,000 labels to the 20,000 VPN routes imported from CE1 and CE2 before advertising these routes to ASRB1. If one-label-per-next-hop label distribution is enabled on PE1, PE1 assigns only one label to the VPN routes with the same next hop and outgoing label. As a result, PE1 assigns only two labels to the 20,000 routes imported from CE1 and CE2 before advertising these routes to ASRB1.

NOTE:

One-label-per-route label distribution and one-label-per-next-hop label distribution can be flexibly switched to each other. During label distribution mode switching, service packets are lost for a short period due to the update of label forwarding tables on the local device and ASBRs.

In an inter-AS VPN Option B scenario, be sure to configure one-label-per-instance label distribution on PEs if you configure one-label-per-next-hop label distribution on ASBRs.

Benefits

Using an appropriate label distribute mode saves label resources.

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Updated: 2018-07-04

Document ID: EDOC1100027166

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