U n i x c i r c l e
FreeBSD FireWall Using IP Filter Via PPPoe
By Hoang Q. TRAN
IT is real simple to build freebsd gateway for a private network. You Only Need to do several tasks. Details Are Given Below.
Lock Down The Box Setup Network Interfaces Customize The Kernel Network Tunings PPPoe Firewall Configure Machines Behind Nat Familiarize with ipfilter Reference
Lock down the boxThe first step in setting up a firewall is to disable any unused services. This helps minimize potential local and remote exploits. Edit /etc/rc.conf and make sure inetd, portmap, sendmail daemons are all disabled.
inetd_enable = "no"
Sendmail_enable = "none"
Check_quotas = "no"
If you don't need Remote Logon, make sure sshd_enable = "no".
Once you disabled unnecessary services, go to unixcircle.com portscan to remotely port scan your own box from the outside. Be careful when you do this behind a NAT / firewall box as the port scan script will scan the NAT / firewall instead. If you Have Another Box, Use nmap to scan the box from the inside.
Get the Latest FreeBSD Security Patches Manually and Apply Them from Here:
ftp://ftp.freebsd.org/pub/freebsd/cert/patches/
OR USE CVSUP TO
Synchronize The Stable Release and Build.
For More Information On Security Vulnerabilities, Read Sans The Twenty Most Critical Internet Security VulneRabilities (Updated)
Setup network interfacesAssume this box has 2 3com 509B network cards and their FreeBSD driver are named as ep0 and ep1 for first and second card. First network card will use the non-routable private address according to rfc1918. The second will be assigned either static or Dynamic Via DHCP IP Address.
Non-Routable IP Addresses for Private Networks: 10.0.0.1 - 10.255.255.254 Netmask 255.0.0.0
172.16.0.1 - 172.31.255.254 Netmask 255.240.0.0
192.168.0.1 - 192.168.255.254 Netmask 255.255.0.0
Assume You Choose 192.168.0.1 Range, Enable The First Network Interface in /etc/rc.conf:
ifconfig_ep0 = "inet 192.168.1.1 Netmask 255.255.255.0"
Customize the KernelTo Compile The New Kernel You NEED The Kernel Source (Part of Kernel Developer Distribution). If you have. '' '' '' '' '
# CD / SYS / I386 / CONF
I usually name the kenel to the machine hostname, but you can give it. Edit The Kernel Config File:
# cp generic firewall
# vi firewall
In The Options Section, Add these Lines for PPPOE:
Options netgraph
Options Netgraph_ETHER
Options netgraph_pppoe
Options netgraph_socket
FireWall and Nat:
Options ipfilter # ipfilter support
Options ipfilter_log # ipfilter logging support
Options ipfilter_default_block # block all packets by Default
Options random_ip_id # random_ip_id causes the ID Field in ip packets to be randomized
# instead of increment by 1 with Each packet generated.
Remove any hardware related `` options '' that are not relevant to your machine. One way to find out what to keep is to consult the dmesg output and remove all the rest. For all available kernel options, refer to LINT in the same directory As The Kernel File. Save The Kernel Config File and The Compile and Install IT:
# CD / USR / SRC
# Make Buildkernel Kernconf = Firewall
(keilding Output ...)
...
# make installkernel kernconf = firewall
# rebootthis will retain the old kernel as /kernel.old Just in case Something Has Gone awry with the new one and the box doesn't boot. if That happens you can type 'kernel.old' at the boot: prompt to boot Old kernel.
Network tuningsadd the folload to /etc/sysctl.conf:
To enable packet forwarding:
Net.inet.ip.Forwarding = 1
To Verify That An Incoming Packet ARRIVES ON ANTERFACE THAT AN Address Matching The Packet's Destination Address:
Net.inet.ip.check_interface = 1
To Drop Syn Packets Destine to Non-Listening TCP / UDP Port. This Will Create A Blackhole and Protect Against Stealth Port Scans:
Net.inet.tcp.blackhole = 2
Net.inet.udp.blackhole = 1
TO Enable High Performance Data TransferS on Hosts According To
Enabling High Performance Data Transfers:
# 1. Path MTU Discovery: enabled by Default
# 2. TCP EXTENSION (RFC1323): Enabled by Default
# 3. Increase TCP Window Size for Increase In Network Performance
Net.inet.tcp.recvspace = 65535
Net.inet.tcp.sendspace = 65535
# 4. Sack (RFC2018): FreeBSD Doesn't Have A Sack Implementation
PPPoe
And if you receive your public address assignment via pppoe, edit /etc/rc.conf and add:
ifconfig_ep1 = "INET 0.0.0.0 MTU 1492"
ifconfig_ep1 = "INET 10.0.0.1 Netmask 255.255.255.0"
PPP_ENABLE = "YES"
PPP_nat = "no"
PPP_MODE = "DDIAL"
PPP_Profile = "Myisp"
Here is a working /etc/ppp/ppp.conf:
DEFAULT:
SET log Phase Chat LCP IPCP CCP TUN COMMAND
Set Redial 15 28800
Set reconnect 15 28800
Myisp:
SET log Phase Chat LCP IPCP CCP TUN COMMAND
Set Device PPPoe: EP1
Set authname xxxyoursecretnamexxx
Set authkey xxxyoursecretkeyxxx
SET MRU 1492
Set MTU 1492
SET CD 5Set Speed Sync
Set Redial 15 28800
Set reconnect 15 28800
Disable LQR
Set Timeout 120
SET IFADDR 10.0.0.1/0 10.0.0.2/0 255.255.255.0 0.0.0.0
Add Default Hisaddr
Firewall
Filter rule:
Since You Don't Know What To Block Yet, You NEED To Open Up Ingress and Outgress Traffic To Flow Through. Edit /etc/ipf.rules and add:
Pass in all
Pass Out All
Network address translation rule:
For Nat and Ftp Clients Behind Nat To Work, Add The Following To /etc/ipnat.rules:
Use ipfilter ftp proxy for ftp client transfers mode: ACTIVE
Map tun0 192.168.1.0/24 -> 0.0.0.0/32 proxy port ftp ftp / tcp
Map all tcp and udp connections from 192.168.1.0/24 to external ip address
Map tun0 192.168.1.0/24 -> 0.0.0.0/32 portmap TCP / UDP 40000: 60000
For all other ip packets, map to the external ip address
Map tun0 192.168.1.0/24 -> 0.0.0.0/32
Make Sure All the `proxy 'Lines Are Before Any Generic` Portmap' Lines, as The First Match Always Wins.
TO Enable FireWall and Nat on bootup, add the folowing to /etc/rc.conf:
ipfilter_enable = "yes" #stateful firewall
IPNAT_ENABLE = "YES" #Network Address TraSlation
IPFS_ENABLE = "YES" #enable saving and reasoning state tables between reboot
IPMON_ENABLE = "YES" #firewall logging
IPMON_FLAGS = "- DSN"
-D: Cause IPMON to Turn Itself Into a daem.
-n: IP Addresses and Port Numbers Will Be mapped, WHERE POSSIBLE, Back Into Hostnames and Service Names.
-s: Packet Information Read in Will Be Sent Through syslogd rather Than Saved to a file.
Configure machines behind NATAll the machines on the private network should be configured to use the address of the private interface of the FreeBSD box as the default gateway.To set the internal boxes to the default FreeBSD gateway on various operating systems:
Assume the FreeBSD Box Nat / Firewall Has IP Address: 192.168.1.1
AIX: edit /etc/rc.net and add / usr / sbin / route add 192.168.1.1 Gateway >> $ logfile 2> & 1
Freebsd: edit /etc/rc.conf and add defaultrouter = "192.168.1.1"
HP-UX: Edit /etc/rc.config.d/netconf and add route_gateway [0] = "192.168.1.1"
Linux redhat: edit / etc / sysconfig / network and add gateway = 192.168.1.1
NetBSD: Echo "192.168.1.1"> / etc / mygate
OpenBSD: Echo "192.168.1.1"> / etc / mygate
Solaris: Echo "192.168.1.1"> / etc / defaultrouter
Win2k: start-settings-> control panel-> network and dial-up connections-> local area network->
Properties-> Internet Protocol (TCP / IP) -> Default Gateway-> 192.168.1.1
IF you don't want to reboot to pick up the ip address for the default gateway, use `` Route '' to manually add the default route.
AIX: Route Add 0 192.168.1.1
HP-UX: Route Add 192.168.1.1
FreeBSD, NetBSD, OpenBSD, Solaris: Route Add Default 192.168.1.1
Linux Redhat: Route Add Default GW 192.168.1.1
2. /etc/resolv.conf on Unix Client Hosts Need To Edit / Add to Have Nameserver Statements in Order To Resolve Hostnames.
UNIX Clients:
$ CAT /ETC/Resolv.conf
Nameserver
Nameserver
Win2k:
Start-settings-> Control Panel-> Network and Dial-Up Connections-> local area network->
Properties-> Internet Protocol (TCP / IP) -> -> Advanced TCP / IP Settings-> DNSAND Add The ISP DNS IPS.
Familiarize with ipfilteronce your nat / firewall is online, you shouth
IP filter howto and add more blocking / passing rules to /etc/ipf.rules. Some Other Useful Links Can Also Be Found ON
IP filter home page. Each time /etc/ipf.rules or /etc/ipnat.rules is modified, you need to flush the rules as:
# / sbin / ipf -fa -f /etc/ipf.rules
# / sbin / ipnat -cf -f -f /etc/ipnat.rules
You can use ipfstat to display firewall statistics a la `` TOP "Command:
# / sbin / ipfstat -t
FireWall.Muine.org - IP Filter: V3.4.29 - State Top 23:01:10
SRC = 0.0.0.0 DEST = 0.0.0.0 proto = any sorted by = # bytes
Source IP Destination IP St Pr #PKTS #BYTES TTL
192.168.1.200, 1415 65.92.100.89, 6699 4/4 TCP 8245 6923504 42:14:06
23.234.234.2, 24064 208.31.160.30, 22 4/4 TCP 576 199843 119: 59: 59
192.168.1.200, 2091 64.124.41.191,8888 4/4 TCP 157 118770 51:36:40
192.168.1.200, 1094 64.124.41.161,8888 4/4 TCP 125 94190 46:37:34
To Find Out The IPfilter Version:
# / sbin / ipf -v
IPF: IP Filter: V3.4.29 (264)
KERNEL: IP Filter: V3.4.29
Running: YES
Log Flags: 0 = none set
Default: Block All, Logging: Available
Active List: 0
Notice the `` block all "setting from ouboptions ipfilter_default_block in the kernel.
To Display THE CURRENT LIST OF Active Map / Redirect Filters and Active Sessions:
# / sbin / ipnat -l
To Find Out The `` Hit "Statistic for Each Individual Rule in /etc/ipf.rules:
# / sbin / ipfstat -hio
See Also ipftest (1), Mkfilters (1), IPF (4), IPL (4), IPF (8), IPFSTAT (8), IPMON (8), IPNAT (8) for Details.Reference
Ipfilter Home Page:
http://www.ipfilter.org
Ipfilter How-to:
http://www.unixcircle.com/ipf/
Address Allocation for Private Internets:
http://www.muine.org/rfc/rfc1918.txt
The IP Network Address Translator (NAT):
http://www.muine.org/rfc/rfc1631.txt
Traditional IP Network Address Translator (Traditional NAT)
http://www.muine.org/rfc/rfc3022.txt
The TWENTY MOST CRITICILIT Security VulneRabilities (Updated)
http://66.129.1.101/top20.htm
Last Update: July 27, 2003
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