Go Back   DaemonForums > Miscellaneous > Guides

Guides All Guides and HOWTO's.

Thread Tools Display Modes
Prev Previous Post   Next Post Next
  #1   (View Single Post)  
Old 1st November 2014
jggimi's Avatar
jggimi jggimi is offline
More noise than signal
Join Date: May 2008
Location: USA
Posts: 6,377
Default Simplyfing complex IPSec or Firewall solutions -- such as NFS -- with gif(4)

The BSDs each have gif(4), a driver that provides a general purpose tunnel interface. You can add them whenever you want to encapsulate IP packets, and tunnel packets inside an outer IP packet. The man pages don't tell you what these are for, or why you would want to use them.

I find gif(4) tunnels helpful whenever I have a complex protocol that is difficult to define in firewall rules or in IPSec flow descriptions. It adds an extra IP header to my data packet, but that tradeoff is usually worth it to provide simple management solutions for what might otherwise be complex or unsolvable problems.

One example is NFS Version 3. It uses Remote Procedure Call programs and dynamic UDP or TCP port numbers, and the port numbers can be unpredictable. What if I wished to encrypt the NFS traffic between client an server, and only the NFS traffic? Or set up a firewall so that only NFS traffic was passed, but not other traffic? Without knowing the dynamic port numbers that will be used, that can be difficult.

Using gif(4), I don't need to know the port numbers. I don't even need to know if the traffic will use TCP or UDP. Instead, I just need to define tunneled, virtual IP addresses and direct all the NFS traffic to them. Then, I write my rules by gif(4) interface or virtual IP address.

For example, I have this gif(4) interface defined on this workstation I'm typing on:

!ifconfig gif0 netmask
This results in the following pseudo-NIC:
    priority: 0
    groups: gif
    tunnel: inet ->
    inet --> netmask 0xffffff00
The real addresses are defined by the tunnel endpoints, which are and The virtual, tunneled addresses are defined as point-to-point between and

The server I am using has a gif(4) configured the same way, but with reversed addresses:
    priority: 0
    groups: gif
    tunnel: inet ->
    inet --> netmask 0xffffff00
The server's /etc/exports permits access from the virtual, tunnelled IP on the workstation.
/var /var/mail
The IPSec rules that define the flows are simple, too. These are from OpenBSD's IKEv2 iked(8) but a similar ruleset could also be applied using the IKEv1 tools:
ikev2  esp \
  from to srcid fw2.jggimi.homeip.net dstid netbook.jggimi.homeip.net
Key: There are only three PF rules that manage this traffic. The gif(4) drivers use IP-in-IP, IP protocol 4, known as ipencap in OpenBSD's /etc/protocols list. That is the only traffic that needs to be passed on the physical interface. On the gif(4) tunnel, I need to pass UDP port 500 for the Internet Key Exchange Protocol (IKE). It is used to manage automatic IPSec keying. I need to pass the IPSec encrypted packets themselves, which is IPSEC tunneling protocol esp.
# allow IPSec under a gif0 tunnel (used for NFS with netbook) 

# 1. permit the gif0 traffic to be embedded on $internal_nic:
pass log on $internal_nic proto ipencap

# 2. permit IKE traffic on UDP port 500 (NAT-Traversal is not used):
pass log on gif0 proto udp from any port 500 to any port 500

# 3. permit IPSec on gif0:
pass log on gif0 proto esp
From my client I can mount the NFS filesystem via fstab(5) or mount(8), as long as I use the virtual address, which I have pre-defined in my local DNS resolver as fw2-gif. Here is an example of monitoring a mail file with xbiff(1):
$ sudo mount fw2-gif:/var/mail /fw2
$ xbiff -file /fw2/jggimi -geometry -4-4 &
Commands/files shown are for OpenBSD. Other BSDs will have varying requirements for provisioning gif(4) interfaces, firewalls, and IPSec.

Last edited by jggimi; 3rd November 2014 at 08:50 PM. Reason: clarity, typos, and a thinko
Reply With Quote

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Some help with IPSEC / VPN Daffy OpenBSD Security 1 9th November 2013 12:45 PM
pkgin accident...any known solutions? enoch82 Other BSD and UNIX/UNIX-like 1 28th April 2013 02:32 PM
IPSec VPN configuration? polken OpenBSD Security 8 29th May 2012 08:48 PM
Need Help Please About IPsec wong_baru FreeBSD Security 2 21st June 2010 08:00 AM
IPsec on openbsd hitete OpenBSD Installation and Upgrading 1 12th July 2008 01:57 AM

All times are GMT. The time now is 11:49 AM.

Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Content copyright © 2007-2010, the authors
Daemon image copyright ©1988, Marshall Kirk McKusick