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Label selection

Label selection

Created: Jun 30, 2020 13:25:24Latest reply: Jun 30, 2020 13:43:35 262 1 0 0 0
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Hello,

The topology is as follows. What does R4 do after R5 allocates Lable 3 to R4 on the network segment 50.5.5.0/24? From which interfaces does it distribute labels? How Does R2 preferentially select a label of the same FEC when receiving different labels from two interfaces?

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Popeye_Wang
Admin Created Jun 30, 2020 13:43:35

Hi,

By default,  the label space type is per platform. Each interface allocates the same label number to the same FEC. In addition, R4 allocates outgoing labels to the received labeled packets. Because by default, split horizon is not enabled, which means that an LSR distributes labels to both upstream and downstream LDP peers.You can use the outbound peer split-horizon command to enable split horizon on an LSR to allow the LSR to distribute labels only to its upstream LDP peers.

https://support.huawei.com/hedex/hdx.do?docid=EDOC1100007335&id=outbound_peer_split-horizon&lang=en

Therefore, R4 will allocate the same label to the FEC for interface E0/0/0 and G0/0/0. 


When AR2 receives two labels of the FEC 50.5.5.0/24, it checks the unicast route to obtain the next hop of 50.5.5.0/24 and compare it with the LDP address (sent when the LDP session is set up). The label sent from the next hop(R4) and can be directly used. The label sent by the non-next hop (R3) is used as the backup label because the device uses the Liberal Label Retention Mode by default.

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Popeye_Wang
Popeye_Wang Admin Created Jun 30, 2020 13:43:35

Hi,

By default,  the label space type is per platform. Each interface allocates the same label number to the same FEC. In addition, R4 allocates outgoing labels to the received labeled packets. Because by default, split horizon is not enabled, which means that an LSR distributes labels to both upstream and downstream LDP peers.You can use the outbound peer split-horizon command to enable split horizon on an LSR to allow the LSR to distribute labels only to its upstream LDP peers.

https://support.huawei.com/hedex/hdx.do?docid=EDOC1100007335&id=outbound_peer_split-horizon&lang=en

Therefore, R4 will allocate the same label to the FEC for interface E0/0/0 and G0/0/0. 


When AR2 receives two labels of the FEC 50.5.5.0/24, it checks the unicast route to obtain the next hop of 50.5.5.0/24 and compare it with the LDP address (sent when the LDP session is set up). The label sent from the next hop(R4) and can be directly used. The label sent by the non-next hop (R3) is used as the backup label because the device uses the Liberal Label Retention Mode by default.

View more
  • x
  • convention：
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