NAME
rtable, rdomain
— routing tables and routing
domains
DESCRIPTION
The traditional kernel routing system had a single table for
routes and allowed only non-conflicting IP address assignments. The
rtable feature allows multiple lookup tables for
routes. The rdomain feature provides a way to
logically segment a router between network paths.
Routing tables
Each rtable contains routes for outbound
network packets. A routing domain can contain more than one
rtable. Multiple routing tables are commonly used
for Policy Based Routing.
The highest ID that can be used for an
rtable is 255.
Routing domains
Each 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 rdomain, but cannot be
assigned more than once per rdomain. An interface
belongs to one and only one rdomain. The interface's
rdomain determines which rdomain an incoming packet
will be in. Virtual interfaces do not need to belong to the same
rdomain as the parent. Each
rdomain contains at least one routing table.
Network traffic within an rdomain stays
within the current routing domain.
pf(4)
is used to move traffic from one rdomain to a
different rdomain.
When an interface is assigned to a non-existent
rdomain it gets created automatically. At the same
time an rtable with the same ID and a
lo(4)
interface with a unit number matching the ID get created and assigned to the
new domain.
An rdomain can be deleted by removing all interfaces from it and then destroying the lo(4) interface with the unit number matching the ID.
The highest ID that can be used for an
rdomain is 255.
EXAMPLES
Put em0 and lo4 in rdomain 4:
# ifconfig em0 rdomain 4 # ifconfig lo4 inet 127.0.0.1/8 # ifconfig em0 192.0.2.100/24
List all rdomains with associated interfaces and routing tables:
$ netstat -RSet a default route and localhost reject route within rtable 4:
# route -T4 -qn add -net 127 127.0.0.1 -reject # route -T4 -n add default 192.0.2.1
Start sshd(8) in rtable 4:
# route -T4 exec
/usr/sbin/sshdDisplay to which rdomain processes are assigned:
$ ps aux -o rtableA pf.conf(5) snippet to block incoming port 80, and nat-to and move to rtable 0 on interface em1:
block in on rdomain 4 proto tcp to any port 80 match out on rdomain 4 to !$internal_net nat-to (em1) rtable 0
Delete rdomain 4 again:
# ifconfig em0 -rdomain # ifconfig lo4 destroy
SEE ALSO
netstat(1), ps(1), lo(4), route(4), pf.conf(5), ifconfig(8), route(8)
HISTORY
OpenBSD support for
rdomain first appeared in OpenBSD
4.9 and IPv6 support first appeared in OpenBSD
5.5.
CAVEATS
No tool is available to assign more than one rtable to an rdomain other than to the default one (0).
An rtable cannot be deleted. Deleting an rdomain will move its rtable into the default rdomain.