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Summary of Landmark / Complete RA for Link Identification

This summary discusses the concept of landmarks and their use in link identification and prefix monitoring. It also explores the weaknesses and strengths of this approach.

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Summary of Landmark / Complete RA for Link Identification

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  1. Summary ofLandmark / Complete RA forLink Identification Brett Pentland – Monash University

  2. Terminology reminder • Point-of-Attachment • Layer two instance to which device connects • E.g. 802.11b access point, Ethernet segment • Link • The set of devices reachable by layer two addressing • E.g. bridged LAN (no router hops) • For IPv6 devices, equivalent to the set of nodes reachable with a link-scope all-hosts multicast packet

  3. Landmarks • Prefix in RS • Landmark Option • Routers monitor all prefixes on link • Routers return the LO in an RA with “yes” or “no” flag set • Unicast • If “yes”, no other configuration options needed • SEND options still needed if applicable

  4. Learned prefixes Learned prefixes Learned prefixes Learned prefixes P6 P5 P3 P1 P2 P6 P4 P7 Unsolicited RA Unsolicited RA Landmark prefix = P1 RS LO = P1 RA LO = P1 (Yes) Prefixes RS LO = P1 RA LO = P1 (No) Prefixes Configured prefixes Configured prefixes P1 R1 R2 P3 P2 P4 L2 Trigger L2 Trigger Configured prefixes Configured prefixes P5 R3 R4 P7 P6 P8

  5. Landmarks (cont.) • Unicast – need rate limiting • Token bucket • Fallback to Complete RA • Unsolicited • Token bucket empty • No LO in RS

  6. Complete RA • Again routers monitor prefixes on link • Already done for Landmarks • Any active prefixes not explicitly configured on router included in DNA option • Flag in RA marks it as complete • Where routers have same prefixes, no DNA option needed (common case) • Hosts - overlap with seen prefixes indicates non-movement • Synchronization between routers not essential • Prefix overlap is the requirement

  7. Learned prefixes Learned prefixes P3 P1 P2 P4 Unsolicited RA Unsolicited RA Unsolicited RA CompleteRA with PIO and DNAO Configured prefixes Configured prefixes P1 R1 R2 P3 P2 P4

  8. Landmark Option Format • Adds 16 octets to RS (typically) 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Pref Length |Y|N| | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Landmark Prefix ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  9. DNA Option Format 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Prefix Len 1 | Prefix Len 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | Prefix Len N | Padding | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Prefix 1 + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Prefix 2 + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Prefix N + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ • Size (octets): • N = number of prefixes on the link but not on sending router • Typically 16N+8 octets (N≤6)

  10. Weaknesses • Modified RS • Landmark Option • Landmark may expose prefix from previous link • Can omit LO and rely on Complete RA • Theoretically size of DNAO is unbounded • In practise, fall back on CPL when DNAO size grows too large

  11. Strengths • Good integration with legacy devices • Absolute answer when moving from non-DNA • Immediate build of CPL • Very small RAs when no link change • Applies rate limiting to unicast RAs • Left out of RFC 2461 – only multicast

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