Summary of Landmark Complete RA for Link Identification

Summary of Landmark / Complete RA for Link Identification Brett Pentland – Monash University

Terminology reminder • Point-of-Attachment – Layer two instance to which device connects – E. g. 802. 11 b access point, Ethernet segment • Link – The set of devices reachable by layer two addressing • E. g. bridged LAN (no router hops) – For IPv 6 devices, equivalent to the set of nodes reachable with a link-scope all-hosts multicast packet

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

Learned prefixes P 3 P 4 Learned prefixes Configured prefixes L 2 Trigger Configured prefixes P 1 R 1 P 2 Unsolicited RA RS LO = P 1 R 2 P 3 P 4 Unsolicited RA RA LO = P 1 (Yes) Prefixes Landmark prefix = P 1 L 2 Trigger Learned prefixes RS LO = P 1 RA LO = P 1 (No) Prefixes P 6 P 7 Learned prefixes Configured prefixes P 5 R 3 P 6 R 4 P 7 P 8

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

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 nonmovement • Synchronization between routers not essential – Prefix overlap is the requirement

Learned prefixes P 3 P 4 Unsolicited RA Learned prefixes Configured prefixes P 1 R 1 P 2 R 2 P 3 P 4 Unsolicited RA Complete. RA with PIO and DNAO

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

DNA Option Format 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 16 N+8 octets (N≤ 6)

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

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