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authorHarald Welte <laforge@gnumonks.org>2015-10-25 21:00:20 +0100
committerHarald Welte <laforge@gnumonks.org>2015-10-25 21:00:20 +0100
commitfca59bea770346cf1c1f9b0e00cb48a61b44a8f3 (patch)
treea2011270df48d3501892ac1a56015c8be57e8a7d /2002/netfilter-knf2002
import of old now defunct presentation slides svn repo
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+Firewalling mit netfilter/iptables unter Linux 2.4.x
+
+Der Linux 2.4.x Kernel bietet eine fortgeschrittene Infrastruktur, genannt
+netfilter, auf deren Basis ein Paketfilter, NAT und sonstige
+Paket-Manipulationen implementiert sind.
+
+Das gesamte Firewalling-Subsystem wurde gegenueber Kernel 2.2.x neu entwickelt.
+Das netfilter/iptables System laesst alles bisher unter Linux existierende
+(ipfwadm, ipchains) wie aus grauer Vorzeit erscheinen.
+
+netfilter/iptables bietet neben dem traditionellen Paketfilter auch optional
+Connection Tracking, mittels dessen sich im Handumdrehen eine Stateful
+Firewall realisieren laesst. Auch das NAT (Network Address Translation)
+System ist jetzt flexibel genug, um saemtliche Formen von NAT anbieten
+zu koennen: source NAT, destination NAT, static NAT, NAPT, ...
+
+Die hohe Modularitaet resultiert in einer sehr leichten Erweiterbarkeit,
+so dass in einfacher Weise neue Erweiterungen zum Firewalling-System
+entwickelt werden koennen.
+
+Der Vortrag beschreibt die unterschiedlichen Teile des netfilter/iptables
+Systems und gibt dadurch einen Ueberblick ueber dessen Moeglichkeiten und
+Anwendungsszenarien. Er beschaeftigt sich mit den folgenden Themen:
+
+- netfilter/iptables architektur
+ - netfilter hooks im Netzwerk-Stack
+ - IP tables als Regelbeschreibung
+- Paketfilter
+- Connection Tracking
+- Network Address Translation
+ - source NAT
+ - destination NAT
+ - Masquerading
+ - transparent proxy support
+- Packet mangling
+- Userspace packet queuing
+- Userspace packet logging
+
+
+Voraussetzungen:
+- Wissen ueber TCP/IP, Routing
+- Grundlagen ueber Firewalling (insbesondere Paketfilter)
+- Gewisse Grundkenntnisse ueber die Linux/Unix Architektur
+
+
+Ueber den Vortragenden:
+Harald Welte ist seit 1995 aktives KNF-Mitglied und der derzeitige
+stellvertretende Technische Kontakt des KNF. Er ist der Maintainer des
+netfilter/iptables Firewalling-Subsystems im Linux 2.4.x und
+2.5.x Kernel und war massgeblich an dessen Entwicklung beteiligt.
diff --git a/2002/netfilter-knf2002/netfilter-knf2002.mgp b/2002/netfilter-knf2002/netfilter-knf2002.mgp
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+%include "default.mgp"
+%default 1 bgrad
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+%nodefault
+%back "blue"
+
+%center
+%size 7
+
+
+The netfilter/iptables framework in
+Linux 2.4.x
+
+
+%center
+%size 4
+by
+
+Harald Welte <laforge@gnumonks.org>
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+netfilter/iptables in Linux 2.4
+Contents
+
+
+ Introduction
+ Netfilter hooks in protocol stacks
+ Packet selection based on IP Tables
+ The Connection Tracking Subsystem
+ The NAT Subsystem based on netfilter + iptables
+ Packet filtering using the 'filter' table
+ Packet mangling using the 'mangle' table
+ Advanced netfilter concepts
+ Current development and Future
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+netfilter/iptables in Linux 2.4
+Introduction
+
+Why did we need netfilter/iptables?
+Because ipchains...
+
+ has no infrastructure for passing packets to userspace
+ makes transparent proxying extremely difficult
+ has interface address dependent Packet filter rules
+ has Masquerading implemented as part of packet filtering
+ code is too complex and intermixed with core ipv4 stack
+ is neither modular nor extensible
+ only barely supports one special case of NAT (masquerading)
+ has only stateless packet filtering
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+netfilter/iptables in Linux 2.4
+Introduction
+
+Who's behind netfilter/iptables
+ Paul 'Rusty' Russel
+ co-author of iptables in Linux 2.2
+ was paid by Watchguard for about one Year of development
+ James Morris
+ userspace queuing (kernel, library and tools)
+ REJECT target
+ Marc Boucher
+ NAT and packet filtering controlled by one command
+ Mangle table
+ Harald Welte
+ Conntrack+NAT helper infrastructure (newnat)
+ Userspace packet logging (ULOG)
+ PPTP and IRC conntrack/NAT helpers
+ Jozsef Kadlecsik
+ TCP window tracking
+ H.323 conntrack + NAT helper
+ Continued newnat development
+ Non-core team contributors
+ http://www.netfilter.org/scoreboard/
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+netfilter/iptables in Linux 2.4
+Netfilter Hooks
+
+What is netfilter?
+
+ System of callback functions within network stack
+ Callback function to be called for every packet traversing certain point (hook) within network stack
+ Protocol independent framework
+ Hooks in layer 3 stacks (IPv4, IPv6, DECnet, ARP)
+ Multiple kernel modules can register with each of the hooks
+ Asynchronous packet handling in userspace (ip_queue)
+
+Traditional packet filtering, NAT, ... is implemented on top of this framework
+
+Can be used for other stuff interfacing with the core network stack, like DECnet routing daemon.
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+netfilter/iptables in Linux 2.4
+Netfilter Hooks
+
+Netfilter architecture in IPv4
+%font "courier"
+
+ --->[1]--->[ROUTE]--->[3]--->[4]--->
+ | ^
+ | |
+ | [ROUTE]
+ v |
+ [2] [5]
+ | ^
+ | |
+ v |
+
+%font "standard"
+1=NF_IP_PRE_ROUTING
+2=NF_IP_LOCAL_IN
+3=NF_IP_FORWARD
+4=NF_IP_POST_ROUTING
+5=NF_IP_LOCAL_OUT
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+netfilter/iptables in Linux 2.4
+Netfilter Hooks
+
+Netfilter Hooks
+
+ Any kernel module may register a callback function at any of the hooks
+
+ The module has to return one of the following constants
+
+ NF_ACCEPT continue traversal as normal
+ NF_DROP drop the packet, do not continue
+ NF_STOLEN I've taken over the packet do not continue
+ NF_QUEUE enqueue packet to userspace
+ NF_REPEAT call this hook again
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+netfilter/iptables in Linux 2.4
+IP tables
+
+Packet selection using IP tables
+
+ The kernel provides generic IP tables support
+
+ Each kernel module may create it's own IP table
+
+ The three major parts of 2.4 firewalling subsystem are implemented using IP tables
+ Packet filtering table 'filter'
+ NAT table 'nat'
+ Packet mangling table 'mangle'
+
+ Can potentially be used for other stuff, i.e. IPsec SPDB
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+netfilter/iptables in Linux 2.4
+IP Tables
+
+Managing chains and tables
+
+ An IP table consists out of multiple chains
+ A chain consists out of a list of rules
+ Every single rule in a chain consists out of
+ match[es] (rule executed if all matches true)
+ target (what to do if the rule is matched)
+
+%size 4
+matches and targets can either be builtin or implemented as kernel modules
+
+%size 6
+ The userspace tool iptables is used to control IP tables
+ handles all different kinds of IP tables
+ supports a plugin/shlib interface for target/match specific options
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+netfilter/iptables in Linux 2.4
+IP Tables
+
+Basic iptables commands
+
+ To build a complete iptables command, we must specify
+ which table to work with
+ which chain in this table to use
+ an operation (insert, add, delete, modify)
+ one or more matches (optional)
+ a target
+
+The syntax is
+%font "typewriter"
+%size 3
+iptables -t table -Operation chain -j target match(es)
+%font "standard"
+%size 5
+
+Example:
+%font "typewriter"
+%size 3
+iptables -t filter -A INPUT -j ACCEPT -p tcp --dport smtp
+%font "standard"
+%size 5
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+netfilter/iptables in Linux 2.4
+IP Tables
+
+Matches
+ Basic matches
+ -p protocol (tcp/udp/icmp/...)
+ -s source address (ip/mask)
+ -d destination address (ip/mask)
+ -i incoming interface
+ -o outgoing interface
+
+ Match extensions (examples)
+ tcp/udp TCP/udp source/destination port
+ icmp ICMP code/type
+ ah/esp AH/ESP SPID match
+ mac source MAC address
+ mark nfmark
+ length match on length of packet
+ limit rate limiting (n packets per timeframe)
+ owner owner uid of the socket sending the packet
+ tos TOS field of IP header
+ ttl TTL field of IP header
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+netfilter/iptables in Linux 2.4
+IP Tables
+
+Targets
+ very dependent on the particular table.
+
+ Table specific targets will be discussed later
+
+ Generic Targets, always available
+ ACCEPT accept packet within chain
+ DROP silently drop packet
+ QUEUE enqueue packet to userspace
+ LOG log packet via syslog
+ ULOG log packet via ulogd
+ RETURN return to previous (calling) chain
+ foobar jump to user defined chain
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+netfilter/iptables in Linux 2.4
+Packet Filtering
+
+Overview
+
+ Implemented as 'filter' table
+ Registers with three netfilter hooks
+
+ NF_IP_LOCAL_IN (packets destined for the local host)
+ NF_IP_FORWARD (packets forwarded by local host)
+ NF_IP_LOCAL_OUT (packets from the local host)
+
+Each of the three hooks has attached one chain (INPUT, FORWARD, OUTPUT)
+
+Every packet passes exactly one of the three chains. Note that this is very different compared to the old 2.2.x ipchains behaviour.
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+netfilter/iptables in Linux 2.4
+Packet Filtering
+
+Targets available within 'filter' table
+
+ Builtin Targets to be used in filter table
+ ACCEPT accept the packet
+ DROP silently drop the packet
+ QUEUE enqueue packet to userspace
+ RETURN return to previous (calling) chain
+ foobar user defined chain
+
+ Targets implemented as loadable modules
+ REJECT drop the packet but inform sender
+ MIRROR change source/destination IP and resend
+ LOG log via syslog
+ ULOG log via userspace
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+netfilter/iptables in Linux 2.4
+Connection Tracking Subsystem
+
+ Connection tracking...
+
+ implemented seperately from NAT
+ enables stateful filtering
+ implementation
+ hooks into NF_IP_PRE_ROUTING to track packets
+ hooks into NF_IP_POST_ROUTING and NF_IP_LOCAL_IN to see if packet passed filtering rules
+ protocol modules (currently TCP/UDP/ICMP)
+ application helpers currently (FTP,IRC,H.323,talk,SNMP)
+ divides packets in the following four categories
+ NEW - would establish new connection
+ ESTABLISHED - part of already established connection
+ RELATED - is related to established connection
+ INVALID - (multicast, errors...)
+ does _NOT_ filter packets itself
+ can be utilized by iptables using the 'state' match
+ is used by NAT Subsystem
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+netfilter/iptables in Linux 2.4
+Network Address Translation
+
+Overview
+
+ Previous Linux Kernels only implemented one special case of NAT: Masquerading
+ Linux 2.4.x can do any kind of NAT.
+ NAT subsystem implemented on top of netfilter, iptables and conntrack
+ NAT subsystem registers with all five netfilter hooks
+ 'nat' Table registers chains PREROUTING, POSTROUTING and OUTPUT
+ Following targets available within 'nat' Table
+ SNAT changes the packet's source whille passing NF_IP_POST_ROUTING
+ DNAT changes the packet's destination while passing NF_IP_PRE_ROUTING
+ MASQUERADE is a special case of SNAT
+ REDIRECT is a special case of DNAT
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+netfilter/iptables in Linux 2.4
+Network Address Translation
+
+ Source NAT
+ SNAT Example:
+%font "typewriter"
+%size 3
+iptables -t nat -A POSTROUTING -j SNAT --to-source 1.2.3.4 -s 10.0.0.0/8
+%font "standard"
+%size 4
+
+ MASQUERADE Example:
+%font "typewriter"
+%size 3
+iptables -t nat -A POSTROUTING -j MASQUERADE -o ppp0
+%font "standard"
+%size 5
+
+ Destination NAT
+ DNAT example
+%font "typewriter"
+%size 3
+iptables -t nat -A PREROUTING -j DNAT --to-destination 1.2.3.4:8080 -p tcp --dport 80 -i eth1
+%font "standard"
+%size 4
+
+ REDIRECT example
+%font "typewriter"
+%size 3
+iptables -t nat -A PREROUTING -j REDIRECT --to-port 3128 -i eth1 -p tcp --dport 80
+%font "standard"
+%size 5
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+netfilter/iptables in Linux 2.4
+Packet Mangling
+
+ Purpose of mangle table
+ packet manipulation except address manipulation
+
+ Integration with netfilter
+ 'mangle' table hooks in all five netfilter hooks
+ priority: after conntrack
+
+ Targets specific to the 'mangle' table:
+ DSCP - manipulate DSCP field
+ IPV4OPTSSTRIP - strip IPv4 options
+ MARK - change the nfmark field of the skb
+ TCPMSS - set TCP MSS option
+ TOS - manipulate the TOS bits
+ TTL - set / increase / decrease TTL field
+
+Simple example:
+%font "typewriter"
+%size 3
+iptables -t mangle -A PREROUTING -j MARK --set-mark 10 -p tcp --dport 80
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+netfilter/iptables in Linux 2.4
+Advanced Netfilter concepts
+
+%size 4
+ Userspace logging
+ flexible replacement for old syslog-based logging
+ packets to userspace via multicast netlink sockets
+ easy-to-use library (libipulog)
+ plugin-extensible userspace logging daemon (ulogd)
+ Can even be used to directly log into MySQL
+
+ Queuing
+ reliable asynchronous packet handling
+ packets to userspace via unicast netlink socket
+ easy-to-use library (libipq)
+ provides Perl bindings
+ experimental queue multiplex daemon (ipqmpd)
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+netfilter/iptables in Linux 2.4
+Current Development and Future
+
+Netfilter (although it proved very stable) is still work in progress.
+
+ Areas of current development
+ infrastructure for conntrack manipulation from userspace
+ failover of stateful firewalls
+ making iptables layer3 independent (pkttables)
+ new userspace library (libiptables) to hide plugins from apps
+ more matches and targets for advanced functions (pool, hashslot)
+ more conntrack and NAT modules (RPC, SNMP, SMB, ...)
+ better IPv6 support (conntrack, more matches / targets)
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+netfilter/iptables in Linux 2.4
+Thanks
+
+ Thanks to
+ the BBS people, Z-Netz, FIDO, ...
+ for heavily increasing my computer usage in 1992
+
+ KNF
+ for bringing me in touch with the internet as early as 1995
+ for providing a playground for technical people
+ for telling me about the existance of Linux!
+
+ Alan Cox, Alexey Kuznetsov, David Miller, Andi Kleen
+ for implementing (one of?) the world's best TCP/IP stacks
+
+ Paul 'Rusty' Russell
+ for starting the netfilter/iptables project
+ for trusting me to maintain it today
+
+ Linux User Group Nuernberg (ALIGN, LUG-N)
+ for helping me with my initial Linux problems
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+netfilter/iptables in Linux 2.4
+Availability of slides / Links
+
+The slides and the an according paper of this presentation are available at
+ http://www.gnumonks.org/
+
+The netfilter homepage
+ http://www.netfilter.org/
+
personal git repositories of Harald Welte. Your mileage may vary