IPv6 Host-to-Router Load Sharing
updates
- rfc-2461 — Neighbor Discovery for IP Version 6 (IPv6)
Extracted elements (8)
A hash-based scheme keyed on destination IP address provides stable per-destination routing even when Destination Cache Entries are deleted, as long as the set of equivalent routers remains unchanged — unlike round-robin which produces path instability on cache eviction.
Always choosing the same router (e.g., first in list) does not provide load sharing. Round-robin and random naive tie-breaking are problematic because cache evictions can produce unstable paths and round-robin can cause synchronization issues where load concentrates on one router.
The document takes no stance on whether load sharing support should be on or off by default, leaving that policy decision to implementations.
This document updates the conceptual sending algorithm in RFC 2461 (Neighbor Discovery for IPv6). The choice of next hop may also affect source address selection per RFC 3484, indirectly influencing inbound router selection as well.
A host that does attempt to distribute load among routers SHOULD use a hash-based scheme that takes (at least) the destination IP address into account, such as those described in RFC 2991, for choosing a router to use.
When a host chooses from multiple equivalent routers, it SHOULD support choosing using some method that distributes load for different destinations among the equivalent routers rather than always choosing the same router.
A malicious local application can bypass the load-sharing algorithm via raw sockets, and remote attackers can still overload routers directly; therefore the hash-based load-sharing mechanisms have no significant incremental impact on Internet infrastructure security.
When next-hop selection is predictable, a remote application can synthesize traffic that hashes identically, enabling a denial-of-service attack against the load-sharing algorithm and overloading a particular router. Using unpredictable hashing makes such attacks harder.