The Everything Feed - All Packet Pushers Pods IPB176: How to Number Point-to-Point Links
May 29, 2025
This discussion dives into the nuances of point-to-point links, revealing why RFC guidelines can sometimes lead you astray. It debates the use of link-local addresses versus global unicast addresses and considers the pros and cons of assigning a /127 versus a /31. The conversation also sheds light on TCAM limitations in network equipment and their impact on routing performance while advocating for simplified neighbor discovery methods. Finally, it navigates the intricacies of IPv4 and IPv6 addressing, encouraging listener engagement with the technical community.
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Link-Local Addresses Enable Adjacency
- Link-local addresses are automatically assigned with a /64 prefix on point-to-point links for neighbor discovery and router adjacency.
- Fully functional neighbor relationships and routing can be established using only link-local addresses without requiring global unicast addresses.
Use /64 Prefixes for Point-to-Points
- Assign /64 global unicast prefixes to point-to-point links in operational settings for consistency and future-proofing.
- Allocate a /64 per point-to-point link even if you later choose to use a shorter prefix length; this preserves flexibility.
IPv6 /127 Prefix History Explained
- Early security issues with IPv6 led to the use of /127 prefixes on point-to-point links to mitigate neighbor discovery vulnerabilities.
- Modern hardware and protocols have resolved these issues, making /64 the operationally preferred prefix length again.