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'll have to add the line options GATEWAY to your
machine's kernel configuration file and re-compile the kernel anyway.
(Trivia: ``Gateways'' are the Internet's old name for what are now
usually called ``routers''.)
Please see the BSD System Manager's Manual chapter on ``Building
Berkeley Kernels with Config'' [the source for which is in
/usr/src/share/doc/smm] and ``FreeBSD Configuration
Options'' [in /sys/doc/options.doc] for more
information on configuring and building kernels. You may have to
unpack the kernel source distribution if haven't installed the system
sources already (srcdist/srcsys.?? in FreeBSD 1.1,
srcdist/sys.?? in FreeBSD 1.1.5.1, or the entire source
distribution in FreeBSD 2.0) to be able to configure and build
kernels.
You'll notice that near the end of the default kernel configuration
file (/sys/i386/conf/GENERICAH) 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.
See the document ``Building Berkeley Kernels with Config'' and the
manual page for config(8) to see how to configure and build
kernels.