Documentation/networking/nexthop-group-resilient.rst

4 Resilient Next-hop Groups
7 Resilient groups are a type of next-hop group that is aimed at minimizing
12 the legacy multipath next-hop group, which uses the hash-threshold
15 To select a next hop, hash-threshold algorithm first assigns a range of
16 hashes to each next hop in the group, and then selects the next hop by
17 comparing the SKB hash with the individual ranges. When a next hop is
19 reassignment of parts of hash space from one next hop to another. RFC 2992
28               Before and after deletion of next hop 3
31 Note how next hop 2 gave up part of the hash space in favor of next hop 1,
33 previous and the new distribution, some traffic flows change the next hop
46 To mitigate the above-mentioned flow redirection, resilient next-hop groups
49 to choose a hash table bucket, then reads the next hop that this bucket
53 algorithm, the range of hashes associated with a next hop must be
55 the individual next hops is arbitrary. Therefore when a next hop is deleted
66 	    Before and after deletion of next hop 3
71 traffic, and use those to satisfy the new next-hop distribution demands,
74 the next-hop group change.
79 In a nutshell, the algorithm works as follows. Each next hop deserves a
82 this number a "wants count" of a next hop. In case of an event that might
100 1) that have no assigned next hop, or
101 2) whose next hop has been removed, or
102 3) that are idle and their next hop is overweight,
104 upkeep changes the next hop that the bucket references to one of the
119 4) whose next hop is overweight, and the amount of time that the table has
129 next hop groups in the following three ways:
145 hop associated with the bucket was removed, and the bucket really must be
184 Next Hop Get
187 Requests to get resilient next-hop groups use the ``RTM_GETNEXTHOP``
188 message in exactly the same way as other next hop get requests. The
205   ``NHA_ID``          ID of the next-hop group that the bucket belongs to.
223   ``NHA_ID``          If specified, limits the dump to just the next-hop group
236                            that contain the next hop with this ID.
249 The last command creates a resilient next-hop group. It will have 8 buckets
255 Changing next-hop weights leads to change in bucket allocation::
272 were migrated after the next-hop replace command to satisfy the new demand
273 that next hop 1 be given 6 buckets instead of 4.
280 For example, the following will mark bucket 23 in next-hop group 10 as