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+%include "default.mgp"
+%default 1 bgrad
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+%nodefault
+%back "blue"
+
+%center
+%size 7
+
+
+The future of Linux packet filtering
+targeted for kernel 2.6
+
+
+%center
+%size 4
+by
+
+Harald Welte <laforge@gnumonks.org>
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+Future of Linux packet filtering
+Contents
+
+
+ Problems with current 2.4.x netfilter/iptables
+ Solution to code replication
+ Solution for dynamic rulesets
+ Solution for API to GUI's and other management programs
+
+ HA for stateful firewalling
+ What's special about firewalling HA
+ Poor man's failover
+ Real state replication
+
+ Other current work
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+Future of Linux packet filtering
+Problems with 2.4.x netfilter/iptables
+
+ code replication between iptables/ip6tables/arptables
+ iptables was never meant for other protocols, but people did copy+paste 'ports'
+ replication of
+ core kernel code
+ layer 3 independent matches (mac, interface, ...)
+ userspace library (libiptc)
+ userspace tool (iptables)
+ userspace plugins (libipt_xxx.so)
+
+ doesn't suit the needs for dynamically changing rulesets
+ dynamic rulesets becomming more common due (service selection, IDS)
+ a whole table is created in userspace and sent as blob to kernel
+ for every ruleset the table needs to be copied to userspace and back
+ inside kernel consistency checks on whole table, loop detection
+
+ too extensible for writing any forward-compatible GUI
+ new extensions showing up all the time
+ a frontend would need to know about the options and use of a new extension
+ thus frontends are always incomplete and out-of-date
+ no high-level API other than piping to iptables-restore
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+Future of Linux packet filtering
+Reducing code replication
+
+ code replication is a real problem: unclean, bugfixes missed
+ we need layer 3 independent layer for
+ submitting rules to the kernel
+ traversing packet-rulesets supporting match/target modules
+ registering matches/targets
+ layer 3 specific (like matching ipv4 address)
+ layer 3 independent (like matching MAC address)
+
+ solution
+ pkt_tables inside kernel
+ pkt_tables_ipv4 registers layer 3 handler with pkt_tables
+ pkt_tables_ipv6 registers layer 3 handler with pkt_tables
+ everybody registering a pkt_table (like iptable_filter) needs to specify the l3 protocol
+ libraries in userspace (see later)
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+Future of Linux packet filtering
+Supporting dynamic rulesets
+
+ atomic table-replacement turned out to be bad idea
+ need new interface for sending individual rules to kernel
+ policy routing has the same problem and good solution: rtnetlink
+ solution: nfnetlink
+ multicast-netlink based packet-orinented socket between kernel and userspace
+ has extra benefit that other userspace processes get notified of rule changes [just like routing daemons]
+ nfnetlink will be low-layer below all kernel/userspace communication
+ pkttnetlink [aka iptnetlink]
+ ctnetlink
+ ulog
+ ip_queue
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+Future of Linux packet filtering
+Communication with other programs
+
+whole set of libraries
+ libnfnetlink for low-layer communication
+ libpkttnetlink for rule modifications
+ will handle all plugins [which are currently part of iptables]
+ query functions about avaliable matches/targets
+ query functions about parameters
+ query functions for help messages about specific match/parameter of a match
+ generic structure from which rules can be built
+ conversion functions to parse generic structure into in-kernel structure
+ conversion functiosn to perse kernel structure into generic structure
+ functions to convert generic structure in plain text
+ libipq will stay API-compatible to current version
+ libipulog will stay API-compatible to current version
+ libiptc will go away [compatibility layer extremely difficult]
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+HA for netfillter/iptables
+Introduction
+
+What is special about firewall failover?
+
+ Nothing, in case of the stateless packet filter
+ Common IP takeover solutions can be used
+ VRRP
+ Hartbeat
+
+ Distribution of packet filtering ruleset no problem
+ can be done manually
+ or implemented with simple userspace process
+
+ Problems arise with stateful packet filters
+ Connection state only on active node
+ NAT mappings only on active node
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+HA for netfillter/iptables
+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
+HA for netfillter/iptables
+Connection Tracking Subsystem
+
+Common structures
+ struct ip_conntrack_tuple, representing unidirectional flow
+ layer 3 src + dst
+ layer 4 protocol
+ layer 4 src + dst
+
+
+ connetions represented as struct ip_conntrack
+ original tuple
+ reply tuple
+ timeout
+ l4 state private data
+ app helper
+ app helper private data
+ expected connections
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+HA for netfillter/iptables
+Connection Tracking Subsystem
+
+Flow of events for new packet
+ packet enters NF_IP_PRE_ROUTING
+ tuple is derived from packet
+ lookup conntrack hash table with hash(tuple) -> fails
+ new ip_conntrack is allocated
+ fill in original and reply == inverted(original) tuple
+ initialize timer
+ assign app helper if applicable
+ see if we've been expected -> fails
+ call layer 4 helper 'new' function
+
+ ...
+
+ packet enters NF_IP_POST_ROUTING
+ do hashtable lookup for packet -> fails
+ place struct ip_conntrack in hashtable
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+HA for netfillter/iptables
+Connection Tracking Subsystem
+
+Flow of events for packet part of existing connection
+ packet enters NF_IP_PRE_ROUTING
+ tuple is derived from packet
+ lookup conntrack hash table with hash(tuple)
+ assosiate conntrack entry with skb->nfct
+ call l4 protocol helper 'packet' function
+ do l4 state tracking
+ update timeouts as needed [i.e. TCP TIME_WAIT,...]
+
+ ...
+
+ packet enters NF_IP_POST_ROUTING
+ do hashtable lookup for packet -> succeds
+ do nothing else
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+HA for netfillter/iptables
+Poor man's failover
+
+Poor man's failover
+ principle
+ let every node do it's own tracking rather than replicating state
+ two possible implementations
+ connect every node to shared media (i.e. real ethernet)
+ forwarding only turned on on active node
+ slave nodes use promiscuous mode to sniff packets
+ copy all traffic to slave nodes
+ active master needs to copy all traffic to other nodes
+ disadvantage: high load, sync traffic == payload traffic
+ IMHO stupid way of solving the problem
+ advantages
+ very easy implementation
+ only addition of sniffing mode to conntrack needed
+ existing means of address takeover can be used
+ same load on active master and slave nodes
+ no additional load on active master
+ disadvantages
+ can only be used with real shared media (no switches, ...)
+ can not be used with NAT
+ remaining problem
+ no initial state sync after reboot of slave node!
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+HA for netfillter/iptables
+Real state replication
+
+Parts needed
+ state replication protocol
+ multicast based
+ sequence numbers for detection of packet loss
+ NACK-based retransmission
+ no security, since private ethernet segment to be used
+ event interface on active node
+ calling out to callback function at all state changes
+ exported interface to manipulate conntrack hash table
+ kernel thread for sending conntrack state protocol messages
+ registers with event interface
+ creates and accumulates state replication packets
+ sends them via in-kernel sockets api
+ kernel thread for receiving conntrack state replication messages
+ receives state replication packets via in-kernel sockets
+ uses conntrack hashtable manipulation interface
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+HA for netfillter/iptables
+Real state replication
+
+ Flow of events in chronological order:
+ on active node, inside the network RX softirq
+ connection tracking code is analyzing a forwarded packet
+ connection tracking gathers some new state information
+ connection tracking updates local connection tracking database
+ connection tracking sends event message to event API
+ on active node, inside the conntrack-sync kernel thread
+ conntrack sync daemon receives event through event API
+ conntrack sync daemon aggregates multiple event messages into a state replication protocol message, removing possible redundancy
+ conntrack sync daemon generates state replication protocol message
+ conntrack sync daemon sends state replication protocol message
+ on slave node(s), inside network RX softirq
+ connection tracking code ignores packets coming from the interface attached to the private conntrac sync network
+ state replication protocol messages is appended to socket receive queue of conntrack-sync kernel thread
+ on slave node(s), inside conntrack-sync kernel thread
+ conntrack sync daemon receives state replication message
+ conntrack sync daemon creates/updates conntrack entry
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+HA for netfillter/iptables
+Neccessary changes to kernel
+
+Neccessary changes to current conntrack core
+
+ event generation (callback functions) for all state changes
+
+ conntrack hashtable manipulation API
+ is needed (and already implemented) for 'ctnetlink' API
+
+ conntrack exemptions
+ needed to _not_ track conntrack state replication packets
+ is needed for other cases as well
+ currently being developed by Jozsef Kadlecsik
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+HA for netfillter/iptables
+Other current work
+
+ optimizing the conntrack code
+ hash function optimization
+ current hash function not good for even hash bucket count
+ other hash functions in development
+ hash function evaluation tool [cttest] avaliable
+ introduce per-system randomness to prevent hash attack
+ code optimization (locking/timers/...)
+
+ getting our work submitted into the mainstream kernel
+ turns out to be more difficult
+ e.g. newnat api now waiting for three months
+
+ discussions about multiple targets/actions per rule
+ technical implementation easy
+ however, not everybody convinced that it fits into the concept
+
+ using tc for firewalling
+ Jamal Hadi Selim uses iptables targets from within TC
+ leads to discussion of generic classification engine API in kernel
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%page
+Future of Linux packet filtering
+Thanks
+ The slides and the an according paper of this presentation are available at http://www.gnumonks.org/
+
+ The netfilter homepage http://www.netfilter.org/
+
+ 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 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
+
personal git repositories of Harald Welte. Your mileage may vary