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route.8: Add information about ROUTE_MPATH and FIB_ALGO

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Since the kernel options ROUTE_MPATH and FIB_ALGO are enabled
per default for a while, it's good to have some user facing
documetation about the general functionality of multipath
routing and fib lookup algorithms.

Reviewed by:	pauamma, Jose Luis Duran <jlduran at gmail dot com>
MFC after:	5 days
Differential Revision:	https://reviews.freebsd.org/D38783
This commit is contained in:
Gordon Bergling 2023-02-26 14:15:34 +01:00
parent f8e1aa85fe
commit b06338167d
1 changed files with 56 additions and 1 deletions
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57
sbin/route/route.8
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@ -28,7 +28,7 @@
.\" @(#)route.8 8.3 (Berkeley) 3/19/94
.\" $FreeBSD$
.\"
.Dd December 15, 2021
.Dd February 26, 2023
.Dt ROUTE 8
.Os
.Sh NAME
@ -405,6 +405,60 @@ and
.Dv RTM_CHANGE .
As such, only the super-user may modify
the routing tables.
.Pp
.Fx provides support for scalable multipath routing.
It is activated by default, but can be turned off by setting the
.Va net.route.multipath
.Xr sysctl 8
MIB to 0.
.Pp
There are multiple route lookup algorithms available.
They can be configured by setting
.Va net.route.algo.inet.algo
for IPv4 and
.Va net.route.algo.inet6.algo
for IPv6
.Xr sysctl 8
MIBs.
.Pp
A list of available algorithms can be obtained by accessing the
following
.Xr sysctl 8
MIBs
.Va net.route.algo.inet.algo_list
for IPv4 and
.Va net.route.algo.inet6.algo_list
for IPv6.
.Pp
The following algorithms are available:
.Bl -tag -width radix_lockless
.It radix
Base system radix backend.
.It bsearch
Lockless binary search in a special IP array, tailored for a small FIB
with <16 routes.
This algorithm is only available for IPv4.
.It radix_lockless
Lockless immutable radix, re-created on every rtable change,
tailored for a small FIB with <1000 routes.
.It dpdk_lpm
DPDK DIR24-8-based lookups, lockless datastructure, optimized
for a large FIB.
In order to use the dpdk_lpm algorithm one or both of the
following kernel modules must be loaded via
.Xr loader.conf 5 :
.Bl -tag -width dpdk_lpm6.ko -compact
.It dpdk_lpm4.ko
DPDK implementation for IPv4.
.It dpdk_lpm6.ko
DPDK implementation for IPv6.
.El
.El
.Pp
The algorithms are selected automatically based on the size of the routing
table of the system.
They can be changed, but not every algorithm performs best for every
FIB size.
.Sh EXIT STATUS
.Ex -std
.Sh EXAMPLES
@ -484,6 +538,7 @@ The next-hop gateway should be reachable through a different route.
.Xr netstat 1 ,
.Xr netintro 4 ,
.Xr route 4 ,
.Xr loader.conf 5 ,
.Xr arp 8 ,
.Xr routed 8
.Sh HISTORY