Q10MPLS and Segment Routing
An engineer is working to implement the segment routing protocol on the customer’s core network. Which step should the engineer take before segment routing is enabled and running with BGP?
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Discussion · 7
C 2
Selected Answer: C
Mulitprotocol Label Switching (MPLS) has to be configured
B 1
Selected Answer: B
A. Segment routing must be configured with EIGRP - This is wrong because EIGRP is usually not used for segment routing.
B. Segment routing must be configured with ISIS - This is probably the correct choice, since ISIS is one of the IGPs that supports segment routing.
C. MPLS must be configured - Segment routing can be implemented with or without MPLS, but traditionally, segment routing has been used with MPLS. However, configuring MPLS is not a prerequisite for segment routing itself; it's more about the data plane technology used to forward packets.
D. Explicit-null must be configured for all neighbors - This is not required for segment routing to function.
The best step before enabling segment routing with BGP would likely be:
B. Segment routing must be configured with ISIS
This makes sure the IGP can support segment routing, which is needed before it can be used together with BGP.
1
Segment Routing (SR) can be used on both MPLS and IPv6 data planes
https://www.cisco.com/c/en/us/td/docs/iosxr/ncs560/segment-routing/79x/b-segment-routing-cg-79x-ncs560/m-configure-srv6-usid-ncs5xx.html#:~:text=Segment%20Routing%20over%20IPv6%20(SRv6)%20extends%20Segment%20Routing%20support%20with,as%20a%20stack%20of%20labels.
1
Hmm, they are not talking about SRv6 (IPV6 data plane). They mentioned only segment routing (SR), which means MPLS is used in the data plane .
but yes this Q is really confused :-)
1
What a terrible question. Both B and C are equally right and wrong. SR doesn't NEED mpls since it can work on pure IPv6, and it also doesn't NEED isis because it can work on OSPF.
From Cisco's own site:
Segment Routing relies on a small number of extensions to Cisco Intermediate System-to-Intermediate System (IS-IS) and Open Shortest Path First (OSPF) protocols. It can operate with an MPLS (Multiprotocol Label Switching) or an IPv6 data plane
1
After thinking about it, I'm going with C. When we say SR, we usually think of SR-MPLS which of course requires MPLS, whereas SRv6 would use IPv6.. bad question either way..
C 1
Selected Answer: C
B looks like the logical answer since configuring SR globally first and then under the routing process automatically enables MPLS on all interfaces enabled for that routing process. However, I go with C because the MPLS dataplane has to be enabled before SR can work. The fact that this is done by enabling SR under the routing process makes this a trick question.