Bering-uClibc 4.x - User Guide - IPv4 Networking - Configure Shorewall

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IPv4 Networking - Configure Shorewall
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Introduction

One of the distinctive feature of LEAF Bering-uClibc (introduced with Bering) is that it relies on Shorewall to provide its firewall facility.

The reasons behind this choice are numerous:

  • Shorewall is an iptables based firewall which offers many features (Masquerading/SNAT, Port forwarding, Static NAT, Proxy ARP, VPN support, Traffic Control/Shaping) which are described in greater detail here.
  • It is a very powerful tool with which it is "simple to do simple things" but which also offers a great flexibility.
  • It is very well documented. We strongly recommend that you have a look at the full documentation available at shorewall.net and that you spend the time to understand the concept behind it. A worthwhile effort !
  • It has a nice QuickStart Guide which will allow the reader to quickly grasp the basics. A prerequisite reading!
  • It has a tremendous support from it's developer, Tom Eastep, who replies very quickly to requests addressed to the shorewall user's mailing list. Mail archives are also available and searchable.


Configuration

To configure Shorewall, start the LEAF packages configuration menu and choose shorwall. The following menu will appear:

                        shorwall configuration files

1) Shorewall Runtime Startup options
2) Params    Assign parameter values
3) Zones     Partition the network into Zones
4) Ifaces    Shorewall Networking Interfaces
5) Hosts     Define specific zones
6) Policy    Firewall high-level policy
7) Rules     Exceptions to policy
8) Masq      Internal MASQ Server Configuration
9) RStopped  Hosts admitted after 'shorewall stop'
10) Nat       Static NAT Configuration
11) Config    Shorewall Global Parameters
12) Modules   Netfilter modules to load
13) TOS       Type of Service policy
14) Blacklist Blacklisted hosts
15) ECN       Disable ECN to hosts and networks
16) Init      Commands executed before [re]start
17) Initdone     Commands executed during [re]start
18) Start     Commands executed after [re]start
19) Started     Commands executed after complete [re]start
20) Stop      Commands executed before stop
21) Stopped   Commands executed after stop
22) Actions   Define user actions
23) Netmap    Network Mapping Table
24) Route_rules Routing to providers
25) Tunnels   Tunnel Definition (ipsec
26) Account   Traffic Accounting Rules
27) TCClasses  Define htb classes
28) TCDevices  Specify speed of devices for traffic shaping
29) TCFilters    Classify traffic for shaping
30) TCInterfaces  Devices for simplified traffic shaping
31) TCPri Classify traffic for simplified traffic shaping
32) TCRules   FWMark Rules
33) Maclist   MAC Verification
34) Providers Additional routing table
35) ProxyArp  Proxy ARP Configuration
36) Notrack  Exclude traffic from connection tracking


  q) quit
  ----------------------------------------------------------------------------
        Selection:

Check the hyperlinks above, the Quickstart Guide or the Shorewall documentation to have a full explanation on those configuration files.

Three files must be checked absolutely to make sure they fit your needs:

A) The zones file (entry 3). For a two interfaces setting - Bering-uClibc's default - it looks like:

 #ZONE   DISPLAY         COMMENTS
 net     ipv4
 loc     ipv4
 #dmz    ipv4
 #LAST LINE - ADD YOUR ENTRIES ABOVE THIS ONE - DO NOT REMOVE

B) The interfaces file (entry 4) defines your interfaces. Default in Bering-uClibc is:

 (...)
 #ZONE   INTERFACE       BROADCAST       OPTIONS
 net     eth0            detect          dhcp
 loc     eth1            detect          dhcp
 #LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE
 

C) The rules file (entry 7) is one of the most important files in Shorewall. Here is the one from Bering-uClibc:

 (...)
 ######################################################################################################
 #ACTION  SOURCE         DEST            PROTO   DEST    SOURCE     ORIGINAL     RATE            USER
 #                                               PORT    PORT(S)    DEST         LIMIT           GROUP
 #                                               PORT    PORT(S)    DEST         LIMIT
 #      Accept DNS connections from the firewall to the network
 #      and from the local network to the firewall (in case dnsmasq is           
 DNS(ACCEPT)   fw          net
 DNS(ACCEPT)   loc         fw

 #      Accept SSH connections from the local network for administrati
 #
 SSH(ACCEPT)   loc         fw

 #      Allow Ping to Firewall                                                   #
 Ping(ACCEPT)  net         fw
 Ping(ACCEPT)  loc         fw

 #      Allow all ICMP types (including ping) from firewall
 ACCEPT    fw           loc                     icmp
 ACCEPT    fw           net                     icmp
 #      Allow local network to access weblet/webconf
 #
 HTTP(ACCEPT)   loc        fw
 HTTPS(ACCEPT)  loc        fw
 # timeserver (allow syncing with time servers (default: pool.ntp.org))                                                        
 NTP(ACCEPT)         fw       net               
 # timeserver (allow LAN clients to sync with the time service on the router)
 # NTP(ACCEPT)         loc    fw
 #LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE

Important: If you change any of the shorewall parameters, remember to save your configuration!


Troubleshooting

  • If you do not have IPv6 enabled (in other words no ipv6.ko Module loaded and no ip6tables.lrp Package installed) then expect to see the following error when (re)starting Shorewall:
    WARNING: DISABLE_IPV6=Yes in shorewall.conf but this system does not appear to have ip6tables
    This is normal and should be ignored. You can always edit /etc/shorewall/shorewall.conf and remove DISABLE_IPV6=Yes to stop the message from appearing.



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