300-510 SPRI: Implementing Cisco Service Provider Advanced Routing SolutionsDemo

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QuestionQ232

MPLS and Segment Routing

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Refer to the exhibit. A network engineer must enable customer connections from PE1 to the external network through the SR-MPLS forwarding plane, using an 8000-SID range. In the current environment:

  • The MPLS forwarding tables on PE1 and PE2 contain LDP-originated LDP labels.
  • The current ranges are 16100–16199 on PE1 and 16200–16299 on PE2.

Which configuration must the engineer apply?

  • A РЕ1 (config)# router isis SR -PE1(config-isis)# segment-routing global-block 1042000 1050000PE1(config-isis)# segment-routing mpls sr-prefer
  • B РЕ1(config)# router isis SR -PE1(config-isis)# segment-routing global-block 16000 24000PE1(config-isis)# address-family ipv4 unicastPE1(config-isis-af)# segment-routing mpls sr-prefer
  • C PE1(config)# router isis SR -PE1(config-isis)# segment-routing global-block 90000 98000PE1(config-isis)# address-family ipv4 unicastPE1(config-isis-af)# segment-routing mpls sr-prefer
  • D РЕ1(config)# router isis SR -PE1(config-isis)# segment-routing global-block 3000 11000PE1(config-isis)# segment-routing mpls sr-prefer
Explanation

The SRGB must reserve a valid label range that does not collide with the existing LDP-assigned labels, and segment-routing mpls sr-prefer under the IS-IS IPv4-unicast address family makes forwarding prefer SR labels over LDP labels. The 90000–98000 block is outside the existing 16100–16299 LDP label ranges, whereas the 16000–24000 block overlaps them. Cisco documents that SRGB values are a reserved range of segment-routing labels and that sr-prefer selects SR labels over LDP labels for the topology.

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