Shorewall and Linux-vserver

Tom Eastep

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover, and with no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License”.

2023/02/18

Table of Contents

Introduction
Vserver Zones
Sharing an IPv6 /64 between Vservers and a LAN

Introduction

Formal support for Linux-vserver was added in Shorewall 4.4.11 Beta2. The centerpiece of that support is the vserver zone type. Vserver zones have the following characteristics:

They are defined on the Linux-vserver host.
The $FW zone is their implicit parent.
Their contents must be defined using the shorewall-hosts (5) file. The ipsec option may not be specified.
They may not appear in the ZONE column of the shorewall-interfaces (5) file.

Note that you don't need to run Vservers to use vserver zones; they may also be used to create a firewall sub-zone for each aliased interface.

If you use these zones, keep in mind that Linux-vserver implements a very weak form of network virtualization:

From a networking point of view, vservers live on the host system. So if you don't use care, Vserver traffic to/from zone z will be controlled by the fw->z and z->fw rules and policies rather than by vserver->z and z->vserver rules and policies.
Outgoing connections from a vserver will not use the Vserver's address as the SOURCE IP address unless you configure applications running in the Vserver properly. This is especially true for IPv6 applications. Such connections will appear to come from the $FW zone rather than the intended Vserver zone.
While you can define the vservers to be associated with the network interface where their IP addresses are added at vserver startup time, Shorewall internally associates all vservers with the loopback interface (lo). Here's an example of how that association can show up:
```
gateway:~# shorewall show zones
Shorewall 4.4.11-Beta2 Zones at gateway - Fri Jul  2 12:26:30 PDT 2010

fw (firewall)
drct (ipv4)
   eth4:+drct_eth4
loc (ipv4)
   eth4:0.0.0.0/0
net (ipv4)
   eth1:0.0.0.0/0
vpn (ipv4)
   tun+:0.0.0.0/0
dmz (vserver)
   lo:70.90.191.124/31

gateway:~#
```

Vserver Zones

This is a diagram of the network configuration here at Shorewall.net during the summer of 2010:

I created a zone for the vservers as follows:

/etc/shorewall/zones:

#ZONE           TYPE            OPTIONS            ...
fw              firewall
loc             ip              #Local Zone
drct:loc        ipv4            #Direct internet access
net             ipv4            #Internet
vpn             ipv4            #OpenVPN clients
dmz             vserver         #Vservers

/etc/shorewall/interfaces:

?FORMAT 2
#ZONE   INTERFACE     OPTIONS
net     eth1          routeback,dhcp,optional,routefilter=0,logmartians,proxyarp=0,nosmurfs,upnp
...

/etc/shorewall/hosts:

#ZONE   HOST(S)                                 OPTIONS
drct    eth4:dynamic
dmz     eth1:70.90.191.124/31                   routeback

While the IP addresses 70.90.191.124 and 70.90.191.125 are configured on eth1, the actual interface name is irrelevant so long as the interface is defined in shorewall-interfaces (5). Shorewall will consider all vserver zones to be associated with the loopback interface (lo). Note that the routeback option is required if the vservers are to be able to communicate with each other.

Once a vserver zone is defined, it can be used like any other zone type.

Here is the corresponding IPv6 configuration.

/etc/shorewall6/zones

#ZONE	TYPE	OPTIONS			IN_OPTIONS			OUT_OPTIONS
fw	firewall
net	ipv6
loc	ipv6
vpn	ipv6
dmz	vserver

/etc/shorewall6/interfaces:

?FORMAT 2
#ZONE   INTERFACE     OPTIONS
net     sit1          tcpflags,forward=1,nosmurfs,routeback
...

/etc/shorewall6/hosts:

#ZONE   HOST(S)                                 OPTIONS
dmz     sit1:[2001:470:e857:1::/64]

Note that I choose to place the Vservers on sit1 (the IPv6 net interface) rather than on eth1. Again, it really doesn't matter much.

Sharing an IPv6 /64 between Vservers and a LAN

I have both a /64 (2001:470:b:227::/64) and a /48 (2001:470:e857::/48) from Hurricane Electric. When I first set up my Vserver configuration, I assigned addresses from the /48 to the Vservers as shown above.

Given that it is likely that when native IPv6 is available from my ISP, I will only be able to afford a single /64, in February 2011 I decided to migrate my vservers to the /64. This was possible because of Proxy NDP support in Shorewall 4.4.16 and later. The new network diagram is as shown below:

This change was accompanied by the following additions to /etc/shorewall6/proxyndp:

#ADDRESS		INTERFACE	EXTERNAL	HAVEROUTE	PERSISTENT
2001:470:b:227::2	-		eth4		Yes		Yes
2001:470:b:227::3	-		eth4		Yes		Yes

These two entries allow the firewall to respond to NDP requests for the two Vserver IPv6 addresses received on interface eth4.

As part of this change, the Lists vserver (OpenSuSE 10.3 was retired in favor of Mail (Debian Squeeze).