IT training linux ip

Guide to IP Layer Network Administration with Linux Version 0.4.4 Martin A Brown SecurePipe, Inc (http://www.securepipe.com/) Network Administration mabrown@securepipe.com Guide to IP Layer Network Administration with Linux: Version 0.4.4 by Martin A Brown Published 2003-04-26 Copyright © 2002, 2003 Martin A Brown This guide provides an overview of many of the tools available for IP network administration of the linux operating system, kernels in the 2.2 and 2.4 series It covers Ethernet, ARP, IP routing, NAT, and other topics central to the management of IP networks Revision History Revision 0.4.4 2003-04-26 Revised by: MAB added index, began packet filtering chapter Revision 0.4.3 2003-04-14 Revised by: MAB ongoing editing, ARP/NAT fixes, routing content Revision 0.4.2 2003-03-16 Revised by: MAB ongoing editing; unreleased version Revision 0.4.1 2003-02-19 Revised by: MAB major routing revision; better use of callouts Revision 0.4.0 2003-02-11 Revised by: MAB major NAT revs; add inline scripts; outline FIB Revision 0.3.9 2003-02-05 Revised by: MAB fleshed out bonding; added bridging chapter Revision 0.3.8 2003-02-03 Revised by: MAB move to linux-ip.net; use TLDP XSL stylesheets Revision 0.3.7 2003-02-02 Revised by: MAB major editing on ARP; minor editing on routing Revision 0.3.6 2003-01-30 Revised by: MAB switch to XSLT processing; minor revs; CVS Revision 0.3.5 2003-01-08 Revised by: MAB ARP flux complete; ARP filtering touched Revision 0.3.4 2003-01-06 Revised by: MAB ARP complete; bridging added; ip neigh complete Revision 0.3.3 2003-01-05 Revised by: MAB split into parts; ARP chapter begun Revision 0.3.2 2002-12-29 Revised by: MAB links updated; minor editing Revision 0.3.1 2002-11-26 Revised by: MAB edited: intro, snat, nat; split advanced in two Revision 0.3.0 2002-11-14 Revised by: MAB chapters finally have good HTML names Revision 0.2.9 2002-11-11 Revised by: MAB routing chapter heavily edited Revision 0.2.8 2002-11-07 Revised by: MAB basic chapter heavily edited Revision 0.2.7 2002-11-04 Revised by: MAB routing chapter finished; links rearranged Revision 0.2.6 2002-10-29 Revised by: MAB routing chapter continued Revision 0.2.5 2002-10-28 Revised by: MAB routing chapter partly complete Revision 0.2.4 2002-10-08 Revised by: MAB advanced routing additions and overview Revision 0.2.3 2002-09-30 Revised by: MAB minor editing; worked on tools/netstat; advanced routing Revision 0.2.2 2002-09-24 Revised by: MAB formalized revisioning; finished basic networking; started netstat Revision 0.2.1 2002-09-21 Revised by: MAB added network map to incomplete rough draft Revision 0.2 2002-09-20 Revised by: MAB incomplete rough draft released on LARTC list Revision 0.1 2002-08-04 Revised by: MAB rough draft begun Table of Contents Introduction .i Target Audience, Assumptions, and Recommendations i Conventions .i Bugs and Roadmap ii Technical Note and Summary of Approach ii Acknowledgements and Request for Remarks ii I Concepts i Basic IP Connectivity IP Networking Control Files Reading Routes and IP Information Sending Packets to the Local Network Sending Packets to Unknown Networks Through the Default Gateway Static Routes to Networks .6 Changing IP Addresses and Routes Changing the IP on a machine Setting the Default Route Adding and removing a static route Conclusion 10 Ethernet 12 Address Resolution Protocol (ARP) .12 Overview of Address Resolution Protocol 12 The ARP cache .15 ARP Suppression 17 The ARP Flux Problem .17 ARP flux prevention with arp_filter .18 ARP flux prevention with hidden 19 Proxy ARP 20 ARP filtering 20 Connecting to an Ethernet 802.1q VLAN 21 Link Aggregation and High Availability with Bonding 22 Link Aggregation 22 High Availability 23 Bridging .25 Concepts of Bridging 25 Bridging and Spanning Tree Protocol 25 Bridging and Packet Filtering .25 Traffic Control with a Bridge 25 ebtables 25 IP Routing 26 Introduction to Linux Routing 26 Routing to Locally Connected Networks .29 Sending Packets Through a Gateway .30 Operating as a Router .31 Route Selection .31 The Common Case 31 iv The Whole Story 32 Summary .34 Source Address Selection .34 Routing Cache 35 Routing Tables 37 Routing Table Entries (Routes) 39 The Local Routing Table 41 The Main Routing Table .43 Routing Policy Database (RPDB) 43 ICMP and Routing 45 MTU, MSS, and ICMP 45 ICMP Redirects and Routing 45 Network Address Translation (NAT) 48 Rationale for and Introduction to NAT 48 Application Layer Protocols with Embedded Network Information .50 Stateless NAT with iproute2 51 Stateless NAT Packet Capture and Introduction 51 Stateless NAT Practicum .52 Conditional Stateless NAT 53 Stateless NAT and Packet Filtering 54 Destination NAT with netfilter (DNAT) 56 Port Address Translation with DNAT 56 Port Address Translation (PAT) from Userspace 57 Transparent PAT from Userspace 57 Masquerading and Source Network Address Translation 58 Concepts of Source NAT 58 Differences Between SNAT and Masquerading 58 Double SNAT/Masquerading 58 Issues with SNAT/Masquerading and Inbound Traffic 58 Where Masquerading and SNAT Break 58 Packet Filtering 59 Rationale for and Introduction to Packet Filtering 59 History of Linux Packet Filter Support .59 Limits of the Usefulness of Packet Filtering .60 Weaknesses of Packet Filtering 61 Complex Network Layer Stateless Packet Filters .61 General Packet Filter Requirements .61 The Netfilter Architecture .62 Packet Filtering with iptables .62 Packet Filtering with ipchains .62 Packet Mangling with ipchains 62 Protecting a Host 62 Protecting a Network 63 Further Resources 63 Statefulness and Statelessness 65 .65 Statelessness of IP Routing 65 Netfilter Connection Tracking 65 v 65 .65 II Cookbook 66 Advanced IP Management 67 Multiple IPs and the ARP Problem 67 Multiple IP Networks on one Ethernet Segment 67 Breaking a network in two with proxy ARP 67 Multiple IPs on an Interface 68 Multiple connections to the same Ethernet 69 Multihomed Hosts 69 Binding to Non-local Addresses 69 10 Advanced IP Routing 70 Introduction to Policy Routing .70 Overview of Routing and Packet Filter Interactions 70 Using the Routing Policy Database and Multiple Routing Tables 71 Using Type of Service Policy Routing 72 Using fwmark for Policy Routing .72 Policy Routing and NAT .72 Multiple Connections to the Internet 72 Outbound traffic Using Multiple Connections to the Internet 73 Inbound traffic Using Multiple Connections to the Internet 75 Using Multiple Connections to the Internet for Inbound and Outbound Connections 77 11 Scripts for Managing IP .79 Proxy ARP Scripts 79 NAT Scripts 82 12 Troubleshooting 90 Introduction to Troubleshooting 90 Troubleshooting at the Ethernet Layer 90 Troubleshooting at the IP Layer .90 Handling and Diagnosing Routing Problems 90 Identifying Problems with TCP Sessions .90 DNS Troubleshooting 90 III Appendices and Reference .91 A An Example Network and Description .92 Example Network Map and General Notes 92 Example Network Addressing Charts 92 B Ethernet Layer Tools 94 arp 94 arping 95 ip link .96 Displaying link layer characteristics with ip link show .96 Changing link layer characteristics with ip link set .97 Deactivating a device with ip link set 98 Activating a device with ip link set 99 Using ip link set to change the MTU 100 Changing the device name with ip link set 100 Changing hardware or Ethernet broadcast address with ip link set 100 vi ip neighbor 101 mii-tool .104 C IP Address Management 107 ifconfig 107 Displaying interface information with ifconfig 107 Bringing down an interface with ifconfig 108 Bringing up an interface with ifconfig 108 Reading ifconfig output 109 Changing MTU with ifconfig .109 Changing device flags with ifconfig 110 General remarks about ifconfig 111 ip address 111 Displaying interface information with ip address show 111 Using ip address add to configure IP address information .112 Using ip address del to remove IP addresses from an interface 113 Removing all IP address information from an interface with ip address flush 114 Conclusion 114 D IP Route Management .116 route .116 Displaying the routing table with route 116 Reading route’s output .117 Using route to display the routing cache 118 Creating a static route with route add 119 Creating a default route with route add default 121 Removing routes with route del .121 ip route .123 Displaying a routing table with ip route show 123 Displaying the routing cache with ip route show cache 125 Using ip route add to populate a routing table 127 Adding a default route with ip route add default 128 Setting up NAT with ip route add nat .128 Removing routes with ip route del 129 Altering existing routes with ip route change 130 Programmatically fetching route information with ip route get 131 Clearing routing tables with ip route flush 131 ip route flush cache 132 Summary of the use of ip route 132 ip rule 133 ip rule show 133 Displaying the RPDB with ip rule show 133 Adding a rule to the RPDB with ip rule add .134 ip rule add nat 135 ip rule del 136 E Tunnels and VPNs .138 Lightweight encrypted tunnel with CIPE 138 GRE tunnels with ip tunnel 138 All manner of tunnels with ssh 138 IPSec implementation via FreeS/WAN .138 vii IPSec implementation in the kernel 138 PPTP 138 F Sockets; Servers and Clients 139 telnet 139 nc 139 socat .140 tcpclient .141 xinetd 141 tcpserver 141 redir 142 G Diagnostics 143 ping .143 Using ping to test reachability 144 Using ping to stress a network 146 Recording a network route with ping 146 Setting the TTL on a ping packet .147 Setting ToS for a diagnostic ping .148 Specifying a source address for ping 149 Summary on the use of ping .149 traceroute 149 Using traceroute 150 Telling traceroute to use ICMP echo request instead of UDP 151 Setting ToS with traceroute .151 Summary on the use of traceroute 151 mtr 151 netstat 151 Displaying socket status with netstat 151 Displaying the main routing table with netstat 154 Displaying network interface statistics with netstat 155 Displaying network stack statistics with netstat 155 Displaying the masquerading table with netstat 155 tcpdump .155 Using tcpdump to view ARP messages .156 Using tcpdump to see ICMP unreachable messages 156 Using tcpdump to watch TCP sessions 157 Reading and writing tcpdump data 157 Understanding fragmentation as reported by tcpdump 158 Other options to the tcpdump command 158 tcpflow 159 tcpreplay 159 H Miscellany 160 ipcalc and other IP addressing calculators 160 Some general remarks about iproute2 tools 160 Brief introduction to sysctl 161 I Links to other Resources 162 Links to Documentation .162 Linux Networking Introduction and Overview Material 162 Linux Security and Network Security .162 viii General IP Networking Resources 162 Masquerading topics 163 Network Address Translation .163 iproute2 documentation 164 Netfilter Resources 164 ipchains Resources 165 ipfwadm Resources 165 General Systems References .165 Bridging 166 Traffic Control 166 IPv4 Multicast 167 Miscellaneous Linux IP Resources 167 Links to Software 168 Basic Utilities 168 Virtual Private Networking software 168 Traffic Control queueing disciplines and command line tools 169 Interfaces to lower layer tools 169 Packet sniffing and diagnostic tools 169 J GNU Free Documentation License 171 PREAMBLE .171 APPLICABILITY AND DEFINITIONS 171 VERBATIM COPYING .172 COPYING IN QUANTITY 172 MODIFICATIONS .173 COMBINING DOCUMENTS .174 COLLECTIONS OF DOCUMENTS 175 AGGREGATION WITH INDEPENDENT WORKS 175 TRANSLATION 175 TERMINATION 176 FUTURE REVISIONS OF THIS LICENSE .176 ADDENDUM: How to use this License for your documents 176 Reference Bibliography and Recommended Reading 178 Index 179 ix List of Tables 2-1 Active ARP cache entry states 15 4-1 Keys used for hash table lookups during route selection 33 5-1 Filtering an iproute2 NAT packet with ipchains .54 A-1 Example Network; Network Addressing 92 A-2 Example Network; Host Addressing 93 B-1 ip link link layer device states 98 B-2 Ethernet Port Speed Abbreviations 104 C-1 Interface Flags 110 C-2 IP Scope under ip address 112 G-1 Possible Session States in netstat output 153 H-1 iproute2 Synonyms .161 List of Examples 1-1 Sample ifconfig output 1-2 Testing reachability of a locally connected host with ping 1-3 Testing reachability of non-local hosts .5 1-4 Sample routing table with a static route .6 1-5 ifconfig and route output before the change 1-6 Bringing down a network interface with ifconfig 1-7 Bringing up an Ethernet interface with ifconfig 1-8 Adding a default route with route 1-9 Adding a static route with route 10 1-10 Removing a static network route and adding a static host route 10 2-1 ARP conversation captured with tcpdump .13 2-2 Gratuitous ARP reply frames .13 2-3 Unsolicited ARP request frames 14 2-4 Duplicate Address Detection with ARP 14 2-5 ARP cache listings with arp and ip neighbor 15 2-6 ARP cache timeout 16 2-7 ARP flux .17 2-8 Correction of ARP flux with conf/$DEV/arp_filter 18 2-9 Correction of ARP flux with net/$DEV/hidden .20 2-10 Bringing up a VLAN interface .21 2-11 Link aggregation bonding 22 2-12 High availability bonding 23 4-1 Classes of IP addresses .27 4-2 Using ipcalc to display IP information .29 4-3 Identifying the locally connected networks with route .29 4-4 Routing Selection Algorithm in Pseudo-code 33 4-5 Listing the Routing Policy Database (RPDB) 33 4-6 Typical content of /etc/iproute2/rt_tables 38 4-7 unicast route types 39 4-8 broadcast route types 39 x Appendix I Links to other Resources Netfilter Resources • Visit Oskar Andreasson’s iptables tutorial (http://iptables-tutorial.frozentux.net) for examples, overview, details, and full documentation of iptables • The netfilter site (http://www.netfilter.org/) provides a wealth of tutorials, examples, documentation, and a mailing list Of particular interest is the documentation section (http://www.netfilter.org/documentation/) • See this brief introduction (http://www.knowplace.org/netfilter/) to packet filtering with iptables • Here is a brief summary of the logging output (http://logi.cc/linux/netfilter-log-format.php3#IPheader) form from the netfilter engine ipchains Resources • Documentation for ipchains (http://www.netfilter.org/ipchains/) is available courtesy of the author, Rusty Russell A mirror of the ipchains HOWTO (http://www.tldp.org/HOWTO/IPCHAINS-HOWTO.html) is available at TLDP • Here is a brief summary of logging output (http://logi.cc/linux/ipchains-log-format.php3)from the kernel • Along wiht a huge pile of other linux-related traffic control and packet filtering documentation, there is a postscript reference card for ipchains (http://snafu.freedom.org/linux2.2/docs/ipchains-refcard.letter.ps) at snafu.freedom.org • ipfwadm Resources • Not covered in this documentation, ipfwadm is only supported in the linux 2.2 and 2.4 kernels via backward compatible interfaces to the internal packet filtering architectures Read more on ipfwadm here (http://www.xos.nl/linux/ipfwadm/paper/) • General Systems References • To learn how to query the kernel’s iptables (http://www.tldp.org/HOWTO/Querying-libiptc-HOWTO/) directly, you need this progamming reference • For a description of the path a frame on the wire takes (http://www.gnumonks.org/ftp/pub/doc/packet-journey-2.4.html) through the kernel from the Ethernet through to the upper layers, Harald Welte’s brief proves instructive 165 Appendix I Links to other Resources • If you are only interested in the path an IP packet takes through the netfilter (ipchains or iptables), routing and ingress/egress QoS code, refer to Stef Coene’s excellent ASCII representation, the kernel 2.4 packet traveling diagram (http://www.docum.org/stef.coene/qos/kptd/) • Oskar Andreasson (of iptables tutorial (http://iptables-tutorial.frozentux.net/) fame) has written an IP sysctl tutorial (http://ipsysctl-tutorial.frozentux.net/) which covers the different /proc filesystem entries (kernel 2.4 only) Bridging • Your linux box can function as a bridge, and two boxen connected to the same hubs can use Spanning Tree Protocol (STP) to protect against failure of one or the other See the Bridge HOWTO (http://www.tldp.org/HOWTO/BRIDGE-STP-HOWTO/index.html) • For a brief article on using a linux bridge as a firewall see David Whitmarsh’s introduction (http://www.sparkle-cc.co.uk/firewall/firewall.html) to the topic • There’s some fledgling documentation of the bridging code in kernel 2.4 (and 2.2) available, especially in conjunction with netfilter here (http://bridge.sourceforge.net/docs/) • Consider also, ebtables (http://users.pandora.be/bart.de.schuymer/ebtables/) named by analogy to iptables If you are bridging at all, or using ebtables at all, you’ll want to know about the interaction between bridging and iptables, so visit the bridge and Netfilter HOWTO (http://www.tldp.org/HOWTO/Ethernet-Bridge-netfilter-HOWTO.html) Traffic Control • The Linux Advanced Routing and Traffic Control (http://lartc.org/) website is the first place to go for any traffic control (and advanced routing) documentation I also recommend the LARTC mailing list (http://mailman.ds9a.nl/mailman/listinfo/lartc) and archive (http://mailman.ds9a.nl/pipermail/lartc/) • Stef Coene has written prodigiously on traffic control under linux (http://www.docum.org/) His site contains practical guidance on traffic control and bandwidth shaping matters • There is an ADSL Bandwidth Management HOWTO (http://www.tldp.org/HOWTO/ADSL-Bandwidth-Management-HOWTO/) on TLDP • Michael Babcock has a page discussing QoS on linux (http://www.fibrespeed.net/~mbabcock/linux/qos_tc/) This is a good introduction, though a bit dated (it seems to discuss only kernel 2.2) • Leonardo Balliache’s has published a brief overview of the compared QoS offerings (http://www.opalsoft.net/qos/) • • Sally Floyd is apparently one of the leading researchers in the use of QoS on the Internet See her work as a researcher at icir.org (http://www.icir.org/floyd/) 166 Appendix I Links to other Resources • Another major research center for QoS under linux is the University of Kansas For some very technical material on QoS under linux, see their main page (http://qos.ittc.ukans.edu/) Here you will find some documentation of the tools available to those programming for QoS implementations under linux • An implementation of DiffServ (http://diffserv.sourceforge.net/), is underway under linux DiffServ is an intermediate step to IntServ There are also the old DiffServ archive (http://www.atm.tut.fi/list-archive/linux-diffserv/thrd6.html) and the current archive (http://sourceforge.net/mailarchive/forum.php?forum=diffserv-general) IPv4 Multicast • A dated multicast routing mini-HOWTO (http://jukie.net/~bart/multicast/Linux-Mrouted-MiniHOWTO.html) provides the best introduction to multicast routing under linux • The smcroute (http://www.cschill.de/smcroute/) utility provides a command line interface to manipulate the multicast routing tables via a method other than mrouted Miscellaneous Linux IP Resources • The sysctl utility is a convenient tool for manipulating kernel parameters Combined with the /etc/sysctl.conf this utility allows an administrator to alter or tune kernel parameters in a convenient fashion across a reboot See this brief RedHat page on the use of sysctl (http://www.redhat.com/docs/manuals/linux/RHL-7.3-Manual/ref-guide/s1-proc-sysctl.html) See also Oskar Andreasson’s IP Sysctl Tutorial (http://ipsysctl-tutorial.frozentux.net/) for a detailed examination of the parameters and their affect on system operation • For users who need to provide a standards compliant VPN solution FreeS/WAN (http://www.freeswan.org/) can be part of a good interoperable solution Additionally, there are issues with using FreeS/WAN on linux as a VPN solution John Denker (appropriate last name) has grappled with the issue of IPSec and routing (http://www.quintillion.com/moat/ipsec+routing/iproute2.html) and has suggested the following work around (http://www.quintillion.com/moat/ipsec+routing/iproute2.html) Here’s a summary of one network admin’s perspective (http://www.quintillion.com/fdis/moat/index.html) on some of the issues related to FreeS/WAN, roving users and network administration for VPN users Note! The 2.5.x development kernel contains an IPSec implementation natively This means that by the release of 2.6.x, linux may support IPSec out of the box • Explicit Congestion Notification (http://www.icir.org/floyd/ecn.html) is supported under linux kernel 2.4 with a sysctl entry • The 2.2 and 2.4 series support bonding of interfaces which allows both link aggregation (IEEE 802.3ad) and failover use of Ethernet interfaces The canonical source for documentation about bonding is Documentation/networking/bonding.txt in the kernel source distribution 167 Appendix I Links to other Resources • If you are looking for virtual router redundancy protocol (VRRP) support under linux, there are several fledgling options The reference implementation (http://w3.arobas.net/~jetienne/vrrpd/) is (according to LARTC scuttlebut) mostly a proof of concpt endeavor At least one other implementation is available for linux and this one has the reputation of being more practical: keepalived (http://www.keepalived.org/) • If you want your linux box to support 802.1q VLAN tagging, you should read up on Ben Greear’s site (http://www.candelatech.com/~greear/vlan.html) • Don’t forget the value of looking for the answer to your question in the linux-net mailing list archive (http://www.uwsg.indiana.edu/hypermail/linux/net/) • Linux Journal has published a two part article on by Gianluca Insolvibile describing the path a packet takes through the kernel Part I covers the input of the packet until just before layer processing (http://www.linuxjournal.com/article.php?sid=4852) Part II covers higher layer packet handling (http://www.linuxjournal.com/article.php?sid=5617), including simple diagram of the kernel’s decisions for each IP packet (http://www.linuxjournal.com/modules/NS-lj-issues/issue95/5617f1.png) • This PDF from the linux-kongress (http://www.linux-kongress.org/2002/papers/lk2002-heuven.pdf) introduces some plans for MPLS and RSVP support under linux (There are also many other interesting papers (http://www.linux-kongress.org/2002/papers/) available here.) Another (the same?) MPLS implementation (http://mpls-linux.sourceforge.net/) is available from SourceForge • A clearly written but probably quite dated introduction (http://www.tldp.org/LDP/tlk/net/net.html) in English to the kernel networking code was written by David Rusling (An update/replacement to this is under development by David Rusling, although no URL is available.) Links to Software Basic Utilities • The net-tools (http://www.tazenda.demon.co.uk/phil/net-tools/) package is a collection of basic utilities for managing the Ethernet and IP layer under linux • The iproute2 package provides command-line support for the full functionality of the linux IP stack This package, written by Alexey Kuznetsov, is available here (ftp://ftp.inr.ac.ru/ip-routing/) and is mirrored here (http://www.linuxgrill.com/anonymous/fire/alexey/) • A tool more convenient than traceroute for tracing routes, mtr (http://www.bitwizard.nl/mtr/) can be obtained here (ftp://ftp.bitwizard.nl/mtr/) • The network swiss army knife of nc (NetCat) (http://www.atstake.com/research/tools/index.html#network_utilities) is available from @stake • For a far more flexible tool in the same vein as nc, socat (http://www.dest-unreach.org/socat/) connects all manner of files, sockets, and file descriptors under most types of unix 168 Appendix I Links to other Resources Virtual Private Networking software • CIPE (http://sites.inka.de/sites/bigred/devel/cipe.html) is a lightweight nonstandard VPN technology which can use shared secrets or RSA keys CIPE is developed primarily for linux but includes a Windows port • For a standards based VPN technology, FreeS/WAN (http://www.freeswan.org/download.html) provides IPSec functionality for the linux kernel If you need an SRPM of the FreeSWAN IPSec software, get it here (http://www.sandelman.ottawa.on.ca/freeswan/rpm/) Note that development kernel 2.5.47+ contains kernel-native support for IPSec Refer to the LARTC IPSec documentation (http://lartc.org/howto/lartc.ipsec.html) for more on this Traffic Control queueing disciplines and command line tools • Martin Devera has written a queueing discipline called HTB (http://luxik.cdi.cz/~devik/qos/htb/) which has been incorporated into the 2.4.20 kernel series As of this writing, HTBv3 is included in kernel 2.4.20+, but tc doesn’t support htb without the patch available here (http://luxik.cdi.cz/~devik/qos/htb/v3/htb3.6-020525.tgz) • Weighted Round Robin is a queueing discipline which distributes bandwidth among the multiple open connections Although the wrr qdisc is not included in the kernel, it is available here (http://wipl-wrr.sourceforge.net/) • Patrick McHardy has written a device which can be used independent of interface to perform traffic shaping The Intermediate Queueing Device (IMQ) (http://trash.net/~kaber/imq/) is supported under kernel 2.4 and provides support for ingress shaping and traffic shaping over multiple physical devices (Site was available here (http://luxik.cdi.cz/~patrick/imq/).) • Werner Almesberger is working on a more user friendly traffic control front end called tcng (http://tcng.sourceforge.net/) This package includes a userspace simulator tcsim • DiffServ • Interfaces to lower layer tools • A collection of various scripts and other interfaces for netfilter is available here (http://www.linuxguruz.org/iptables/) • A curses-based tool ipmenu (http://users.pandora.be/stes/ipmenu.html) provides a single uniform interface to many of the IP layer features of linux • • 169 Appendix I Links to other Resources Packet sniffing and diagnostic tools • The tcpdump (http://www.tcpdump.org/) utility is a well known cross-platform utility for sniffing traffic on the wire • To watch plaintext protocol conversations, the tcpflow (http://www.circlemud.org/~jelson/software/tcpflow/) tool can be invaluable • To gather data on the nature and quality of the network path between two points, the bing (http://www.cnam.fr/reseau/bing.html) program provides a running set of statistics by calculating the delta between ICMP echo replies from different hosts • To help diagnose problems between network points, the pathchar (http://www.caida.org/tools/utilities/others/pathchar/) tool can be handy Unfortunately, it only comes in a binary release, apparently because Van Jacobsen did not feel it was ready for full release • • Among the sniffing and spoofing tools, dsniff (http://monkey.org/~dugsong/dsniff/) has received good press It is a collection of tools for network auditing and penetration testing • If you need to capture and reinject packets into the network, libnet (http://www.packetfactory.net/Projects/Libnet/) is a library you can use for these purposes This is a diagnostic and security tool • To reproduce traffic from a captured file, use tcpreplay (http://tcpreplay.sourceforge.net/) 170 Appendix J GNU Free Documentation License Copyright (C) 2000,2001,2002 Free Software Foundation, Inc 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed PREAMBLE The purpose of this License is to make a manual, textbook, or other functional and useful document "free" in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either 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accept compensation in exchange for copies If you distribute a large enough number of copies you must also follow the conditions in section You may also lend copies, under the same conditions stated above, and you may publicly display copies 172 Appendix J GNU Free Documentation License COPYING IN QUANTITY If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document’s license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover Both covers must also clearly and legibly identify you as the publisher of these copies The front cover must present the full title with all words of the title equally prominent and visible You may add other material on the covers in addition Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using public-standard network protocols a complete Transparent copy of the Document, free of added material If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document MODIFICATIONS You may copy and distribute a Modified Version of the Document under the conditions of sections and above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it In addition, you must these things in the Modified Version: A Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document) You may use the same title as a previous version if the original publisher of that version gives permission B List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has fewer than five), unless they release you from this requirement C State on the Title page the name of the publisher of the Modified Version, as the publisher D Preserve all the copyright notices of the Document E Add an appropriate copyright notice for your modifications adjacent to the other copyright notices 173 Appendix J GNU Free Documentation License F Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below G Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document’s license notice H Include an unaltered copy of this License I Preserve the section Entitled "History", Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page If there is no section Entitled "History" in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence J Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on These may be placed in the "History" section You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission K For any section Entitled "Acknowledgements" or "Dedications", Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein L Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles Section numbers or the equivalent are not considered part of the section titles M Delete any section Entitled "Endorsements" Such a section may not be included in the Modified Version N Do not retitle any existing section to be Entitled "Endorsements" or to conflict in title with any Invariant Section O Preserve any Warranty Disclaimers If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant To this, add their titles to the list of Invariant Sections in the Modified Version’s license notice These titles must be distinct from any other section titles You may add a section Entitled "Endorsements", provided it contains nothing but endorsements of your Modified Version by various parties for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one The author(s) and publisher(s) of the Document not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version 174 Appendix J GNU Free Documentation License COMBINING DOCUMENTS You may combine the Document with other documents released under this License, under the terms defined in section above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work In the combination, you must combine any sections Entitled "History" in the various original documents, forming one section Entitled "History"; likewise combine any sections Entitled "Acknowledgements", and any sections Entitled "Dedications" You must delete all sections Entitled "Endorsements" COLLECTIONS OF DOCUMENTS You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document AGGREGATION WITH INDEPENDENT WORKS A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an "aggregate" if the copyright resulting from the compilation is not used to limit the legal rights of the compilation’s users beyond what the individual works permit When the Document is included an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document If the Cover Text requirement of section is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document’s Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form Otherwise they must appear on printed covers that bracket the whole aggregate TRANSLATION Translation is considered a kind of modification, so you may distribute translations of the Document 175 Appendix J GNU Free Documentation License under the terms of section Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections You may include a translation of this License, and all the license notices in the Document, and any Warrany Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail If a section in the Document is Entitled "Acknowledgements", "Dedications", or "History", the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title TERMINATION You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License Any other attempt to copy, modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance FUTURE REVISIONS OF THIS LICENSE The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns See http://www.gnu.org/copyleft/ Each version of the License is given a distinguishing version number If the Document specifies that a particular numbered version of this License "or any later version" applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation ADDENDUM: How to use this License for your documents To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page: Copyright (c) YEAR YOUR NAME Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts A copy of the license is included in the section entitled "GNU Free Documentation License" If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the "with Texts." line with this: 176 Appendix J GNU Free Documentation License with the Invariant Sections being LIST THEIR TITLES, with the Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software 177 Reference Bibliography and Recommended Reading Chandra Kopparapu, 2002, 0-471-41550-2, Load Balancing Servers, Firewalls, and Caches, John Wiley & Sons, Inc W Richard Stevens, 1994, 0-201-63346-9 (v.1), TCP/IP Illustrated, Volume I, Addison Wesley Robert L Ziegler, 2001, 0-2357-1099-6, Linux Firewalls, New Riders Tony Mancill, 2000, 0-1308-6113-8, Linux Routers, Prentice Hall 178 Index 179 ... command suite, written specificially for linux Because this guide concerns itself with the features, strengths, and peculiarities of IP networking with linux, the iproute2 command suite assumes... C-6 Displaying IP information with ip address 111 C-7 Adding IP addresses to an interface with ip address 112 C-8 Removing IP addresses from interfaces with ip address ... network with ip route add nat 129 D-23 Removing routes with ip route del 11 130 D-24 Altering existing routes with ip route change 130 D-25 Testing routing tables with ip route