Frequently Asked Questions for FreeBSD 8.`X`, and 9.`X`
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# Chapter 11 Networking

11.1. Where can I get information on “diskless booting”?
11.2. Can a FreeBSD box be used as a dedicated network router?
11.3. Can I connect my Windows® box to the Internet via FreeBSD?
11.4. Does FreeBSD support PPP?
11.5. Does FreeBSD support NAT or Masquerading?
11.6. How can I set up Ethernet aliases?
11.7. Why can I not NFS-mount from a Linux® box?
11.8. Why does `mountd` keep telling me it “`can't change attributes`” and that I have a “`bad exports list`” on my FreeBSD NFS server?
11.9. How do I enable IP multicast support?
11.10. Why do I have to use the FQDN for hosts on my site?
11.11. Why do I get an error, “`Permission denied`”, for all networking operations?
11.12. Why is my `ipfw` “fwd” rule to redirect a service to another machine not working?
11.13. How can I redirect service requests from one machine to another?
11.14. Where can I get a bandwidth management tool?
11.15. Why do I get “`/dev/bpf0: device not configured`”?
11.16. How do I mount a disk from a Windows machine that is on my network, like smbmount in Linux?
11.17. What are these messages about: “`Limiting icmp/open port/closed port response`” in my log files?
11.18. What are these “`arp: unknown hardware address format`” error messages?
11.19. Why do I keep seeing messages like: “`192.168.0.10 is on fxp1 but got reply from 00:15:17:67:cf:82 on rl0`”, and how do I disable it?

11.1. Where can I get information on “diskless booting”?

“Diskless booting” means that the FreeBSD box is booted over a network, and reads the necessary files from a server instead of its hard disk. For full details, please read the Handbook entry on diskless booting.

11.2. Can a FreeBSD box be used as a dedicated network router?

Yes. Please see the Handbook entry on advanced networking, specifically the section on routing and gateways.

11.3. Can I connect my Windows® box to the Internet via FreeBSD?

Typically, people who ask this question have two PCs at home, one with FreeBSD and one with some version of Windows the idea is to use the FreeBSD box to connect to the Internet and then be able to access the Internet from the Windows box through the FreeBSD box. This is really just a special case of the previous question and works perfectly well.

Dialup users must use `-nat` and set `gateway_enable` to YES in `/etc/rc.conf`. For more information, please see the ppp(8) manual page or the Handbook entry on user PPP.

If you are using kernel-mode PPP or have an Ethernet connection to the Internet, you need to use natd(8). Please look at the natd section of the Handbook for a tutorial.

11.4. Does FreeBSD support PPP?

Yes. ppp(8) provides support for both incoming and outgoing connections.

For more information on how to use this, please see the Handbook chapter on PPP.

11.5. Does FreeBSD support NAT or Masquerading?

Yes. If you want to use NAT over a user PPP connection, please see the Handbook entry on user PPP. If you want to use NAT over some other sort of network connection, please look at the natd section of the Handbook.

11.6. How can I set up Ethernet aliases?

If the alias is on the same subnet as an address already configured on the interface, then add `netmask 0xffffffff` to your ifconfig(8) command-line, as in the following:

    # ifconfig ed0 alias 192.0.2.2 netmask 0xffffffff

Otherwise, just specify the network address and netmask as usual:

    # ifconfig ed0 alias 172.16.141.5 netmask 0xffffff00

You can read more about this in the FreeBSD Handbook.

11.7. Why can I not NFS-mount from a Linux® box?

Some versions of the Linux NFS code only accept mount requests from a privileged port; try to issue the following command:

    # mount -o -P linuxbox:/blah /mnt

11.8. Why does `mountd` keep telling me it “`can't change attributes`” and that I have a “`bad exports list`” on my FreeBSD NFS server?

The most frequent problem is not understanding the correct format of `/etc/exports`. Please review exports(5) and the NFS entry in the Handbook, especially the section on configuring NFS.

11.9. How do I enable IP multicast support?

FreeBSD supports multicast host operations by default. If you want your box to run as a multicast router, you need to recompile your kernel with the `MROUTING` option and run mrouted(8). FreeBSD will start mrouted(8) at boot time if the flag `mrouted_enable` is set to `YES` in `/etc/rc.conf`.

> Note: In recent FreeBSD releases, the mrouted(8) multicast routing daemon, the map-mbone(8) and mrinfo(8) utilities have been removed from the base system. These programs are now available in the FreeBSD Ports Collection as `net/mrouted`.

11.10. Why do I have to use the FQDN for hosts on my site?

See the answer in the FreeBSD Handbook.

11.11. Why do I get an error, “`Permission denied`”, for all networking operations?

If you have compiled your kernel with the `IPFIREWALL` option, you need to be aware that the default policy is to deny all packets that are not explicitly allowed.

If you had unintentionally misconfigured your system for firewalling, you can restore network operability by typing the following while logged in as `root`:

    # ipfw add 65534 allow all from any to any

You can also set `firewall_type="open"` in `/etc/rc.conf`.

For further information on configuring a FreeBSD firewall, see the Handbook chapter.

11.12. Why is my `ipfw` “fwd” rule to redirect a service to another machine not working?

Possibly because you want to do network address translation (NAT) and not just forward packets. A “fwd” rule does exactly what it says; it forwards packets. It does not actually change the data inside the packet. Say we have a rule like:

    01000 fwd 10.0.0.1 from any to foo 21

When a packet with a destination address of `foo` arrives at the machine with this rule, the packet is forwarded to `10.0.0.1`, but it still has the destination address of `foo`! The destination address of the packet is not changed to `10.0.0.1`. Most machines would probably drop a packet that they receive with a destination address that is not their own. Therefore, using a “fwd” rule does not often work the way the user expects. This behavior is a feature and not a bug.

See the FAQ about redirecting services, the natd(8) manual, or one of the several port redirecting utilities in the Ports Collection for a correct way to do this.

11.13. How can I redirect service requests from one machine to another?

You can redirect FTP (and other service) request with the `sysutils/socket` port. Simply replace the service's command line to call `socket` instead, like so:

    ftp stream tcp nowait nobody /usr/local/bin/socket socket ftp.example.com ftp

where `ftp.example.com` and `ftp` are the host and port to redirect to, respectively.

11.14. Where can I get a bandwidth management tool?

There are three bandwidth management tools available for FreeBSD. dummynet(4) is integrated into FreeBSD as part of ipfw(4). ALTQ has been integrated into FreeBSD as part of pf(4). Bandwidth Manager from Emerging Technologies is a commercial product.

11.15. Why do I get “`/dev/bpf0: device not configured`”?

You are running a program that requires the Berkeley Packet Filter (bpf(4)), but it is not in your kernel. Add this to your kernel config file and build a new kernel:

    device bpf        # Berkeley Packet Filter

11.16. How do I mount a disk from a Windows machine that is on my network, like smbmount in Linux?

Use the SMBFS toolset. It includes a set of kernel modifications and a set of userland programs. The programs and information are available as mount_smbfs(8) in the base system.

11.17. What are these messages about: “`Limiting icmp/open port/closed port response`” in my log files?

This is the kernel telling you that some activity is provoking it to send more ICMP or TCP reset (RST) responses than it thinks it should. ICMP responses are often generated as a result of attempted connections to unused UDP ports. TCP resets are generated as a result of attempted connections to unopened TCP ports. Among others, these are the kinds of activities which may cause these messages:

- Brute-force denial of service (DoS) attacks (as opposed to single-packet attacks which exploit a specific vulnerability).

- Port scans which attempt to connect to a large number of ports (as opposed to only trying a few well-known ports).

The first number in the message tells you how many packets the kernel would have sent if the limit was not in place, and the second number tells you the limit. You can control the limit using the `net.inet.icmp.icmplim` sysctl variable like this, where `300` is the limit in packets per second:

    # sysctl net.inet.icmp.icmplim=300

If you do not want to see messages about this in your log files, but you still want the kernel to do response limiting, you can use the `net.inet.icmp.icmplim_output` sysctl variable to disable the output like this:

    # sysctl net.inet.icmp.icmplim_output=0

Finally, if you want to disable response limiting, you can set the `net.inet.icmp.icmplim` sysctl variable (see above for an example) to `0`. Disabling response limiting is discouraged for the reasons listed above.

11.18. What are these “`arp: unknown hardware address format`” error messages?

This means that some device on your local Ethernet is using a MAC address in a format that FreeBSD does not recognize. This is probably caused by someone experimenting with an Ethernet card somewhere else on the network. You will see this most commonly on cable modem networks. It is harmless, and should not affect the performance of your FreeBSD machine.

11.19. Why do I keep seeing messages like: “`192.168.0.10 is on fxp1 but got reply from 00:15:17:67:cf:82 on rl0`”, and how do I disable it?

Because a packet is coming from outside the network unexpectedly. To disable them, set `net.link.ether.inet.log_arp_wrong_iface` to `0`.

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