OpenBSD manual page server

Manual Page Search Parameters

RDOMAIN(4) Device Drivers Manual RDOMAIN(4)

rtable, rdomainrouting tables and routing domains

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.

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.

Each rdomain is a completely separate address space in the kernel. An IP address (e.g. 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.

The highest ID that can be used for an rdomain is 255.

Set up em0 and lo4 onto rdomain 4:

# ifconfig em0 rdomain 4
# ifconfig lo4 inet
# ifconfig em0

Set a default route and localhost reject route within rdomain 4:

# route -T4 -qn add -net 127 -reject
# route -T4 -n add default

Start an sshd in rdomain 4:

# route -T4 exec /usr/sbin/sshd

Display to which rdomain processes are assigned:

# ps aux -o rtable

pf.conf 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

ps(1), lo(4), route(4), pf.conf(5), ifconfig(8), route(8)

OpenBSD support for rdomains first appeared in OpenBSD 4.9 and IPv6 support first appeared in OpenBSD 5.5.

When an rtable already exists a new domain with the same ID cannot be created. Since there is no command to destroy an rtable a reboot is necessary.

No tool is available to assign more than one rtable to an rdomain other than to the default one (0).

November 14, 2016 OpenBSD-6.1