352-001 · Question #746
The CTO of XYZ is having some high-level discussions about IPv6 implementation and is considering whether XYZ should consider the MPLS IPv6 Provider Edge approach. Which two drawbacks of the MPLS…
The correct answer is C. MPLS P routers cannot send ICMPv6 messages because they are not enable for IPv6 D. Single RIB and FIB is required for each connected customer, so scalability issues can arise. MPLS IPv6 Provider Edge has drawbacks including the inability of core P routers to send ICMPv6 messages and per-customer RIB/FIB requirements that limit scalability.
Question
The CTO of XYZ is having some high-level discussions about IPv6 implementation and is considering whether XYZ should consider the MPLS IPv6 Provider Edge approach. Which two drawbacks of the MPLS IPv6 Provider Edge approach are true? (Choose two)
Options
- AXYZ must migrate the IGP used in the MPLS core network to the multitopology IS-IS architecture
- BThe label allocation mode is per-prefix. so the label table grows as the BGP table increases
- CMPLS P routers cannot send ICMPv6 messages because they are not enable for IPv6
- DSingle RIB and FIB is required for each connected customer, so scalability issues can arise
- ESingle IGP topology must be deployed, which can cause scalability issues in the future
How the community answered
(24 responses)- A8% (2)
- B17% (4)
- C54% (13)
- E21% (5)
Why each option
MPLS IPv6 Provider Edge has drawbacks including the inability of core P routers to send ICMPv6 messages and per-customer RIB/FIB requirements that limit scalability.
Migration to multitopology IS-IS is a requirement associated with running native IPv6 alongside IPv4 in the MPLS core IGP, not a drawback specific to the MPLS IPv6 PE edge approach.
Per-prefix label allocation causing label table growth is a characteristic concern of 6PE deployments, not a defining drawback of the MPLS IPv6 PE architecture.
In the MPLS IPv6 PE model, core P routers operate purely at the MPLS label level and are not IPv6-enabled, so they cannot generate ICMPv6 messages such as Packet Too Big, which impairs path MTU discovery and network troubleshooting.
Each customer connected to a PE router requires a separate RIB and FIB instance (typically a VRF), and as the number of customers grows, this per-customer forwarding state creates significant scalability challenges for PE hardware and software resources.
Single IGP topology scalability constraints are a concern in certain dual-stack core designs but are not a primary or defining drawback of the MPLS IPv6 PE provider edge approach.
Concept tested: MPLS IPv6 Provider Edge architecture drawbacks
Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/configuration/xe-16/irg-xe-16-book/bgp-ipv6-provider-edge-routers-6vpe.html
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