Copyright (c) 2015 Peter Hessler <phessler@openbsd.org>
Permission to use, copy, modify, and distribute this software for any
purpose with or without fee is hereby granted, provided that the above
copyright notice and this permission notice appear in all copies.
THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.Dd $Mdocdate: March 31 2022 $ .Dt RDOMAIN 4 .Os .Sh NAME .Nm rtable , .Nm rdomain .Nd routing tables and routing domains .Sh DESCRIPTION The traditional kernel routing system had a single table for routes and allowed only non-conflicting IP address assignments. The .Nm rtable feature allows multiple lookup tables for routes. The .Nm rdomain feature provides a way to logically segment a router between network paths. .Ss Routing tables Each .Nm rtable contains routes for outbound network packets. A routing domain can contain more than one .Nm rtable . Multiple routing tables are commonly used for Policy Based Routing.
p The highest ID that can be used for an .Nm rtable is 255. .Ss Routing domains Each .Nm rdomain is a completely separate address space in the kernel. An IP address (e.g. 10.0.0.1/16) can be assigned in more than one .Nm rdomain , but cannot be assigned more than once per .Nm rdomain . An interface belongs to one and only one .Nm rdomain . The interface's .Nm rdomain determines which rdomain an incoming packet will be in. Virtual interfaces do not need to belong to the same .Nm rdomain as the parent. Each .Nm rdomain contains at least one routing table.
p Network traffic within an .Nm rdomain stays within the current routing domain. .Xr pf 4 is used to move traffic from one .Nm rdomain to a different .Nm rdomain .
p When an interface is assigned to a non-existent .Nm rdomain , it gets created automatically. At the same time an .Nm rtable with the same ID and a .Xr lo 4 interface with a unit number matching the ID get created and assigned to the new domain.
p An rdomain can be deleted by removing all interfaces from it and then destroying the .Xr lo 4 interface with the unit number matching the ID.
p The highest ID that can be used for an .Nm rdomain is 255. .Sh EXAMPLES Put em0 and lo4 in rdomain 4: d -literal -offset indent # ifconfig em0 rdomain 4 # ifconfig lo4 inet 127.0.0.1/8 # ifconfig em0 192.0.2.100/24 .Ed
p List all rdomains with associated interfaces and routing tables:
p .Dl $ netstat -R
p Set a default route and localhost reject route within rtable 4: d -literal -offset indent # route -T4 -qn add -net 127 127.0.0.1 -reject # route -T4 -n add default 192.0.2.1 .Ed
p Start .Xr sshd 8 in rtable 4:
p .Dl # route -T4 exec /usr/sbin/sshd
p Display the routing table used by each process:
p .Dl $ ps aux -o rtable
p Display the routing table of the current process:
p .Dl $ id -R
p A .Xr pf.conf 5 snippet to block incoming port 80, and nat-to and move to rtable 0 on interface em1: d -literal -offset indent block in on rdomain 4 proto tcp to any port 80 match out on rdomain 4 to !$internal_net nat-to (em1) rtable 0 .Ed
p Delete rdomain 4 again: d -literal -offset indent # ifconfig em0 -rdomain # ifconfig lo4 destroy .Ed .Sh SEE ALSO .Xr id 1 , .Xr netstat 1 , .Xr ps 1 , .Xr lo 4 , .Xr route 4 , .Xr pf.conf 5 , .Xr ifconfig 8 , .Xr route 8 .Sh HISTORY .Ox support for .Nm rdomain first appeared in .Ox 4.9 and IPv6 support first appeared in .Ox 5.5 . .Sh CAVEATS No tool is available to assign more than one rtable to an rdomain other than to the default one (0).
p An rtable cannot be deleted. Deleting an rdomain will move its rtable into the default rdomain.