FAQ-Why does traffic forwarding fail when the L3VPN label distribution method changes from per-route label to per-instance label

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For S series switches (except S1700 switches), why does traffic forwarding fail when the L3VPN label distribution method changes from per-route label to per-instance label?

When this problem occurs, check whether a large number of BGP LSPs exist on the switch before the change of the label distribution method. (BGP LSPs occupy resources in the MPLS decapsulation table.)
In V200R003 and earlier versions, the per-route label distribution method is used for L3VPN. The number of entries in the MPLS decapsulation table of a switch is limited. Besides, the MPLS decapsulation table is a hash table and may encounter hash collisions. When there are a large number of local routes for an L3VPN, many entries in the MPLS decapsulation table are occupied. The per-instance label distribution method is recommended in this case.
When the label distribution method changes from per-route label to per-instance label, new BGP LSPs are generated in the VPN instance. If a large number of BGP LSPs exist on the switch before the change, the new BGP LSPs may cause hash collisions in the MPLS decapsulation table. As a result, traffic forwarding fails in the L3VPN.

Operation Notes:
Before changing the label distribution method to per-instance label on the switch, check the number of existing BGP LSPs. If there are a large number of BGP LSPs, withdraw local routes in the L3VPN to reduce the number of BGP LSPs, and then change the label distribution method.

Other related questions:
FAQ-How private network labels are distributed on an L3VPN
For S series switches (except S1700 switches), private network labels are distributed on an L3VPN using either of the following ways: 1. One label per VPN instance 2. One label per VPN route (default method) When a large number of VPN routes exist on a network, many private network labels are required if the default label distribution method is used. These private network labels may use up all entries. In this case, each VPN instance can be allocated a private network label to reduce the chip entries used.

How private network labels are distributed on an L3VPN
Private network labels can be distributed in either of the following ways: 1.One label per VPN instance 2.One label per VPN route When a large number of VPN routes exist on a network, many private network labels are required if one VPN route is allocated with one label. These private network labels may use up all entries. In this case, each VPN instance can be allocated a private network label to reduce the chip entries used.

Displaying the e-label on the firewall
Perform as follows to view the e-label on the firewall: display elabel Syntax display elabel [ slot-id ] Parameter description slot-id specifies the ID of the slot where the board is inserted. Example Display the e-label of the board in slot 0. display elabel 0

How to view the electronic labels
You can use commands to view the electronic labels. To view the part number and production date, run the display elabel command. [Board Properties] BoardType=CX22EMFF BarCode=21023514201091000095 Item=02351420 Description=S3752P-EI-48S, S3752P-EI-48S Mainframe(48 100 BASE-X ports and 2 100/1000 BASE-X ports and 2 SFP GE (1000 BASE-X) ports (SFP Req.) and DC -48V) Manufactured=2009-01-24 VendorName=Huawei IssueNumber=00 CLEICode= BOM=02351420 BarCode: electronic label Manufactured: production date BOM: part number

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