FreeBSD's default kernels usually come with two SLIP interfaces
defined (sl0 and sl1); you can use netstat
-i to see whether these interfaces are defined in your kernel.
Sample output from netstat -i:
Name Mtu Network Address Ipkts Ierrs Opkts Oerrs Coll
ed0 1500 <Link>0.0.c0.2c.5f.4a 291311 0 174209 0 133
ed0 1500 138.247.224 ivory 291311 0 174209 0 133
lo0 65535 <Link> 79 0 79 0 0
lo0 65535 loop localhost 79 0 79 0 0
sl0* 296 <Link> 0 0 0 0 0
sl1* 296 <Link> 0 0 0 0 0
The sl0 and sl1 interfaces shown in netstat
-i's output indicate that there are two SLIP interfaces built
into the kernel. (The asterisks after the sl0 and
sl1 indicate that the interfaces are ``down''.)
However, FreeBSD's default kernels do not come configured to forward
packets (ie, your FreeBSD machine will not act as a router) due to
Internet RFC requirements for Internet hosts (see RFC's 1009
[Requirements for Internet Gateways], 1122
[Requirements for Internet Hosts -- Communication Layers],
and perhaps 1127 [A Perspective on the Host Requirements
RFCs]), so if you want your FreeBSD SLIP Server to act as a
router, you will have to edit the /etc/rc.conf file (called
/etc/sysconfig in FreeBSD releases prior to 2.2.2) and change
the setting of the gateway variable to YES. If you
have an older system which predates even the /etc/sysconfig
file, then add the following command:
sysctl -w net.inet.ip.forwarding = 1to your
/etc/rc.local file.
You will then need to reboot for the new settings to take effect.
You will notice that near the end of the default kernel configuration
file (/sys/i386/conf/GENERIC) is a line that reads:
pseudo-device sl 2
which is the line that defines the number of SLIP devices available in the kernel; the number at the end of the line is the maximum number of SLIP connections that may be operating simultaneously.
Please refer to Configuring the FreeBSD Kernel for help in reconfiguring your kernel.