diff options
Diffstat (limited to '2007/netfilter-iptables-tfh2007')
| -rw-r--r-- | 2007/netfilter-iptables-tfh2007/netfilter-iptables.mgp | 706 |
1 files changed, 706 insertions, 0 deletions
diff --git a/2007/netfilter-iptables-tfh2007/netfilter-iptables.mgp b/2007/netfilter-iptables-tfh2007/netfilter-iptables.mgp new file mode 100644 index 0000000..4172e97 --- /dev/null +++ b/2007/netfilter-iptables-tfh2007/netfilter-iptables.mgp @@ -0,0 +1,706 @@ +%include "default.mgp" +%default 1 bgrad +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +%nodefault +%back "blue" + +%center +%size 7 + + +netfilter/iptables +%size 4 + +Jan 29, 2007 +TFH Berlin + +%center +%size 4 +by + +Harald Welte <laforge@netfilter.org> + + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +Contents + + Introduction + Highly Scalable Linux Network Stack + Netfilter Hooks + Packet selection based on IP Tables + The Connection Tracking Subsystem + The NAT Subsystem + Packet Mangling + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +Introduction + + +Who is speaking to you? + an independent Free Software developer + who earns his living off Free Software since 1997 + who is one of the authors of the Linux kernel packet filter + busy with enforcing the GNU GPL at gpl-violations.org + working on Free Software for smartphones (openEZX, OpenMoko)` + ... and Free Software for RFID (librfid) + ... and Free Software for ePassports (libmrtd) + ... and Free Hardware for RFID (openpcd.org, openbeacon.org) + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +Introduction + +Linux and Networking + Linux is a true child of the Internet + Early adopters: ISP's, Universities + Lots of work went into a highly scalable network stack + Not only for client/server, but also for routers + Features unheared of in other OS's + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +Introduction + +Did you know, that a stock 2.6.x linux kernel can provide + + a stateful packet filter ? + fully symmetric NA(P)T ? + policy routing ? + QoS / traffic shaping ? + IPv6 firewalling ? + packet filtering, NA(P)T on a bridge ? + layer 2 (mac) address translation ? + packet forwarding rates of up to 2.1Mpps (in 2005)? + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +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 tutorial +Introduction + +Who's behind netfilter/iptables + + The core team + Paul 'Rusty' Russel + co-author of iptables in Linux 2.2 + James Morris + Marc Boucher + Harald Welte + Jozsef Kadlecsik + Martin Josefsson + Patrick McHardy + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +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 + +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 tutorial +Netfilter Hooks + +Netfilter architecture in IPv4 +%font "typewriter" +%size 4 +in --->[1]--->[ROUTE]--->[3]--->[4]---> out + | ^ + | | + | [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 tutorial +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 tutorial +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 four major parts of the firewalling subsystem are implemented using IP tables + Packet filtering table 'filter' + NAT table 'nat' + Packet mangling table 'mangle' + The 'raw' table for conntrack exemptions + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +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) + implicit packet and byte counter + +%size 4 +matches and targets can either be builtin or implemented as kernel modules + +%size 5 + 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 tutorial +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 tutorial +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 + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +IP Tables + + addrtype match + matches source/destionation address type + types are UNICAST/LOCAL/BROADCAST/ANYCAST/MULTICAST/... + ah match + matches IPSEC AH SPI (range) + comment match + always matches, allows user to place comment in rule + connmark match + connection marking, see later + conntrack match + more extended version of 'state' + match on timeout, fine-grained state, original tuples + dscp match + matches DSCP codepoint (formerly-known as TOS bits) + + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +IP Tables + + ecn match + matches ECN bits of tcp and ip header + esp match + matches IPSEC ESP SPI (range) + hashlimit match + dynamic limiting + helper match + allows matching of conntrack helper name + iprange match + match on arbitrary IP address ranges (not a mask) + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +IP Tables + + length match + match on packet length + limit + static rate limiting + mac + match on source mac address + mark + match on nfmark (fwmark) + multiport + match on multiple ports + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +IP Tables + + owner + match on socket owner (uid, gid, pid, sid, command name) + physdev + match underlying device in case of bridge + pkttype + match link-layer packet type (unicast,broadcast,multicast) + realm + match routing realm + recent + see special section below + tcpmss + match on TCP maximum segment size + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +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 tutorial +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 tutorial +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 + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +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/SCTP) + application helpers currently (FTP,IRC,H.323,talk,SNMP) + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +Connection Tracking Subsystem + + Connection tracking... + + 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 tutorial +Connection Tracking Subsystem + + State tracking for TCP is obvious + TCP inherently stateful + Two TCP state machines on each end have well-defined behaviour + Passive tracking of state machines + In more recent 2.6.x kernels, tracking of TCP window (seq/ack) + Max idle timeout of fully-established session: 5 days + + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +Connection Tracking Subsystem + + State tracking for UDP: How is this possible? + UDP itself not stateful at all + However, higher-level protocols mostly match request-reply + First packet (request) is assumed to be NEW + First matching reply packet is assumed to confirm connection + Further packets in either direction refresh timeout + Timeouts: 30sec unreplied, 180sec confirmed + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +Connection Tracking Subsystem + + State tracking on ICMP: What's that? + ICMP Errors (e.g. host/net unreachable, ttl exceeded) + They can always be categorized as RELATED to other connections + ICMP request/reply (ECHO REQUEST, INFO REQUEST) + can be treated like UDP request/reply case + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +Connection Tracking Subsystem + + State tracking on SCTP: What's SCTP? + Streaming Control Transfer Protocol + Linux has SCTP in the network stack, so why should the packet filter not support it? + Pretty much like TCP in most cases + Doesn't support more advanced features such as failover of an endpoint + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +Connection Tracking Subsystem + + State tracking on other protocols + 'generic' protocol: no layer-4 tuple information + 'gre' helper in patch-o-matic + + State tracking of higher-layer protocols + implemented as 'connection tracking helpers' + currently in-kernel: amanda, ftp, irc, tftp + currently in patch-o-matic: pptp, h.323, sip, quake, ... + have to be explicitly loaded (ip_conntrack_*.[k]o) + work by issuing so-called "expectations" + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +Connection Tracking Subsystem + + Exemptions to connection tracking + Usually connection tracking is called first in PRE_ROUTING + Sometimes, filtering is preferred before this conntrack lookup + Therefore, the "raw" table was introduced + In some rare cases, one might want to not track certain packets + The NOTRACK can be used in the "raw" table + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +Connection Tracking Subsystem + + Configuration / Tuning + module parameter "hashsize" + number of hash table buckets + /proc/sys/net/ipv4/ip_conntrack_max + maximum number of tracked connections + /proc/sys/net/ipv4/ip_conntrack_buckets (read-only) + number of hash table buckets + /proc/net/ip_conntrack + list of connections + /proc/net/ip_conntrack_expect + list of pending expectations + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +Connection Tracking Subsystem + + Configuration / Tuning + /proc/sys/net/ip_conntrack_log_invalid + log invalid packets? + /proc/sys/net/ip_conntrack_tcp_be_liberal + basically disables window tracking, if "1" + /proc/sys/net/ip_conntrack_tcp_loose + how many packets required until sync in case of pickup + if set to zero, disables pickup + /proc/sys/net/ip_conntrack_tcp_max_retrans + maximum number of retransmitted packets without seeing a n ACK + /proc/sys/net/ip_conntrack_*timeout* + timeout values of respective protocol states + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +Network Address Translation + + Network Address Translation + + Previous Linux Kernels only implemented one special case of NAT: Masquerading + Linux 2.4.x / 2.6.x can do any kind of NAT. + NAT subsystem implemented on top of netfilter, iptables and conntrack + 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 + SAME + NETMAP + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +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 tutorial +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 + +Simple example: +%font "typewriter" +%size 3 +iptables -t mangle -A PREROUTING -j MARK --set-mark 10 -p tcp --dport 80 + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +Packet Mangling + + Targets specific to the 'mangle' table: + DSCP + manipulate DSCP field + ECN + manipulate ECN bits + 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 + CLASSIFY + classify packet (for tc/iproute) + CONNMARK + set mark of connection + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +The raw Table + + Purpose of 'raw' table + to allow for filtering rules _before_ conntrack + Targets specific to the 'raw' table: + NOTRACK + don't do connection tracking + + The table can also be useful for flood protection rules that happen before traversing the (computational) expensive connection tracking subsystem. + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +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 tutorial +Advanced Netfilter concepts + + Firewalling on a Bridge (ebtables + iptables) + totally transparent to layer 2 and above + no attack vector since firewall has no IP address + even possible to do NAT on the bridge + or even NAT of MAC addresses + + ipset - Faster matching + iptables are a linear list of rules + ipset represents a 'group' scheme + Implements different data types for different applications + hash table (for random addresses) + bitmask (for let's say a /24 network) + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +Advanced Netfilter concepts + + ipv6 packet filtering + ip6tables almost identical to iptables + no connection tracking in mainline yet, but patches exist + ip6_conntrack + initial copy+paste 'port' by USAGI + was not accepted because of code duplication + nf_conntrack + generalized connection tracking, supports ipv4 and ipv6 + mutually exclusive with ip_conntrack + up to 2.6.20, no ipv4 nat on to of nf_conntrack + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%page +netfilter/iptables tutorial +Thanks + + Thanks to + the BBS scene, Z-Netz, FIDO, ... + for heavily increasing my computer usage in 1992 + KNF (http://www.franken.de/) + for bringing me in touch with the internet as early as 1994 + 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 + Astaro AG + for sponsoring parts of my netfilter work |