CCDE: Cisco Certified Design Expert (Written) — Question 41

Two MPLS service providers (SP1 and SP2) are offering inter-provider RFC 2547/4364-based IP-VPN service to an enterprise customer. IP traffic among some of the customer's sites has to traverse both of the service providers. The service providers and the enterprise do not know what the minimum MTU is along the end- to-end path.
What could be done to guarantee that large packets are not dropped for MTU-related reasons?

Answer options

• A. enable Path MTU Discovery on all devices within SP1 and SP2
• B. enable Path MTU Discovery on all devices within the enterprise
• C. configure the IP sender or senders to set the DF flag in the IP header
• D. configure the IP sender or senders to clear the DF flag in the IP header

Correct answer: B

Explanation

Enabling Path MTU Discovery on all devices within the enterprise ensures that the network can discover the smallest MTU along the path, preventing packet drops. While enabling Path MTU Discovery on SP1 and SP2 could help, it is crucial that the enterprise devices also support this feature for optimal results. The options regarding the DF flag do not resolve MTU-related issues effectively, as they either prevent fragmentation or allow it, but do not actively discover the path's MTU.