TCP/IP Networking

1. TCP/IP Networking • Objectives – to learn how to integrate a RedHat system onto a TCP/IP network • Contents – the TCP/IP protocol suite – IP addressing – basic TCP/IP applications – TCP/IP configuration files • Practicals – working with TCP/IP utilities and files • Summary

2. Overview of TCP/IP • US DoD funded experimental network – supports inter-networks, inter-host communication – most popular UNIX networking protocols • Three basic protocols TCP - a reliable session protocol: telnet, ftp UDP - low overhead sessionless: NFS, NIS, DNS, routing IP - Network layer protocol, sessionless, base of TCP and UDP network gateway hosts

3. Internet Protocol Address • All networked systems need a unique IP address – address has four dot separated numbers (each 0 - 255) – IP address mapped to hardware using ARP or RARP protocols • Companies allocated a site address by NIC – allocated class A B or C address ranges – local administrator allocates individual host numbers • Some address values reserved 0 not used 255 reserved for broadcasts • Network address of 127 is reserved for loopback • Network address of 10 is reserved for internal networks • Network addesss of 172.16 is reserved for internal networks • Network addesss of 192.168 is reserved for internal networks

4. IP Address Format network 24 bit host address Class A Addresses 7 bits 8 bits 24 bits 0 network addresses in range 0 - 126 16 bit network 16 bit host address Class B Addresses 1 0 14 bits 16 bits network addresses in range 128.0 - 191.254 24 bit network 8 bit host Class C Addresses 8 bits 1 1 0 21 bits network addresses in range 192.0.0 - 223.254.254

5. Defining IP Addresses • Traditionally IP address defined in /etc/hosts – one line per known host defining IP address hostname and aliases – if last line is a + then NIS is being used – hostnames are limited to 8 characters • Larger sites use DNS (Domain Name Services) – one or more hosts on the network maintain all IP addresses – individual hosts request addresses as needed – address cached locally to optimise DNS # more /etc/hosts 127.0.0.1 localhost.localdomain localhost mash4077 loghost mailhost rosies seoul 192.168.0.12 192.168.0.42 10.1.1.1 printserver

6. Analyze Network Interface Configuration • Use ifconfig to view network interfaces – use the -a option to list all configured interfaces # ifconfig -a eth0 Link encap:Ethernet HWaddr 00:50:04:50:61:98 inet addr:192.168.1.100 Bcast:192.168.1.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:59078481 errors:0 dropped:0 overruns:84 frame:0 TX packets:53902612 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:22596609 errors:0 dropped:0 overruns:0 frame:0 TX packets:22596609 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 # ifconfig eth0 down # ifconfig eth0 up

7. Network Interface Configuration • Use ifconfig to configure the network interface # ifconfig eth0 192.168.0.1 netmask 255.255.255.0 up • Permanent changes in /etc/sysconfig/network-scripts Files named like: ifcfg-eth0 STATIC settings: DHCP settings: DEVICE=eth0 BOOTPROTO=dhcp ONBOOT=yes DEVICE=eth0 USERCTL=no ONBOOT=yes BOOTPROTO=none BROADCAST=192.168.0.255 NETWORK=192.168.0.0 NETMASK=255.255.255.0 IPADDR=192.168.0.1 • Alias interfaces # Ifconfig eth0:0 192.168.1.12 Permanent changes in /etc/sysconfig/network-scripts/ifcg-eth0:0 With DEVICE=eth0:0 • Releasing/Renewing IP adresses ifdown eth0 / ifdown eth0

8. Routing information • Use route to get/manipulate network routing – Route table netstat –r(n) or route – Routes to all directly connected networks are created automatic – To add a net-route: route add –net 192.168.7.0 gw 192.168.1.254 – To delete a net-route: route del –net 192.168.7.0 gw 192.168.1.254 • Redhat can hande RIP/OSPF + traffic shaping Metric value for priority if different value or round robin if same: route add –net 192.168.3.0 netmask 255.255.255.0 gw 192.168.1.253 metric 10 route add –net 192.168.3.0 netmask 255.255.255.0 gw 192.168.1.254 metric 10 Detete the route: route del –net 192.168.3.0 netmask 255.255.255.0 # route Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 80.84.37.0 * 255.255.255.240 U 0 0 0 eth3 172.16.0.0 * 255.255.255.0 U 0 0 0 eth2 192.168.1.0 * 255.255.255.0 U 0 0 0 eth0 192.168.0.0 * 255.255.255.0 U 0 0 0 eth1 127.0.0.0 * 255.0.0.0 U 0 0 0 lo default router.ing-stee 0.0.0.0 UG 0 0 0 eth3

9. Routing information configuration • Use route to configure the defaultrouter # route add default gw 192.168.1.1 eth0 # route add default gw 192.168.1.1 eth0 • Permanent changes in /etc/sysconfig/ Files named network: GATEWAYDEV=eth0 NETWORKING=yes FORWARD_IPV4=yes NISDOMAIN=nis.ikea.se HOSTNAME=node01.ikea.se GATEWAY=80.84.37.1 • Using several routes # route add route add - -net 10.0.0.0 netmask 255.0.0.0 gw 192.168.1.254 eth0 net 10.0.0.0 netmask 255.0.0.0 gw 192.168.1.254 eth0 Permanent changes in /etc/sysconfig/static-routes eth0 net 10.0.0.0 netmask 255.0.0.0 gw 192.168.1.254 eth0 net 10.0.0.0 netmask 255.0.0.0 gw 192.168.1.254 Or better use /etc/rc.d/rc.local route add route add - -net 10.0.0.0 netmask 255.0.0.0 gw 192.168.1.254 eth0 net 10.0.0.0 netmask 255.0.0.0 gw 192.168.1.254 eth0

10. Adding/Removing NIC’s Adding NIC 1. Before going further, find out current NIC-order a) By physical inspection, pinging and moving cables. b) Look in /etc/modprobe.conf or find NIC modules with lsmod and ksyms –m or –am Kernel key symbol is exported like [3c59x] for 3c905 boards. c) Modify /etc/modprobe.conf to reflect your wished NIC order. 2. Look if new NIC needs to be added in kernel or kernel need patch. If that is the case, recompile kernel and do step 1 again! 3. Power off the host 4. Insert the new NIC 5. If you are lucky, kudzu will find the new NIC and add it for you, you will be asked configuration parameters. NOTE! Kudzu can destroy current configuration in /etc/modprobe.conf and change Nic order. 6. If everything goes well you can now goto step 1 once again to check out your NIC order. If you are satisfied it is time to do NIC configuration permanent. • Removing NIC, you basically do the same steps but you now remove support, kudzu will detect NIC removal and you can remember its configuration.

11. Changing NIC parameters • Use mii-tool to view NIC settings # mii # mii- -tool tool – –v v [steen@lina sysconfig]$ mii [steen@lina sysconfig]$ mii- -tool eth0: negotiated 100baseTx-FD, link ok product info: vendor 00:10:18, model 18 rev 0 basic mode: autonegotiation enabled basic status: autonegotiation complete, link ok capabilities: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD advertising: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD link partner: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD flow- control tool - -v | more v | more • Using mii-tool to force 100MBit/s Full Duplex # mii-tool -F 100baseTx-FD eth0 • Making changes permanent /etc/rc.d/rc.local

12. Nameservers for non nameserver hosts • Nameservers are stored in /etc/resolv.conf General format: domain my-site.com search my-site.com nameserver ip 2 nameserver ip 1 nameserver ip 3 The nameservers to query for names My domain, my host is added to this domain. A space delimited list of max six key domains to add hostnames to in the query if domain is missing. rotate round robin Nameserver list timeout:n default is 30 seconds attempts:n default is 3 or 4 • Searchorder for finding hosts are stored in /etc/host.conf order hosts,bind Nameserver Domain Search Options • Name Service Switch config file /etc/nsswitch.conf Hosts: files dns

13. Looking at Network Statistics • Use netstat to get network status information – use -a to view all sockets – use -i to view interfaces – use -rn to view routing statistics # netstat -i Kernel Interface table Iface MTU Met RX-OK RX-ERR RX-DRP RX-OVR TX-OK TX-ERR TX-DRP TX-OVR Flg eth0 1500 0 59098394 0 0 84 53924429 0 0 0 BRU lo 16436 0 22598046 0 0 0 22598046 0 0 0 LRU

14. Looking for a System • The simplest TCP/IP utility is ping which sends a message to a host and waits for a reply – the host can be specified as a name or an IP address $ ping –c1 gkse1 PING gkse1.ing-steen.se (80.84.37.2) from 80.84.37.3 : 56(84) bytes of data. 64 bytes from gkse1.ing-steen.se (80.84.37.2): icmp_seq=0 ttl=64 time=1.119 mse --- gkse1.ing-steen.se ping statistics --- 1 packets transmitted, 1 packets received, 0% packet loss round-trip min/avg/max/mdev = 1.119/1.119/1.119/0.000 ms $ ping ulf2 PING ulf2.intra.ing-steen.se (192.168.1.37) from 192.168.1.100 : 56(84) bytes of data. From lina.intra.ing-steen.se (192.168.1.100): Destination Host Unreachable --- ulf2.intra.ing-steen.se ping statistics --- 1 packets transmitted, 0 packets received, +1 errors, 100% packet loss $ ping dude ping: unknown host dude

15. Network layer 2 • To see if you have contact with network layer 2 – use ifconfig Shows if interfaces are up – use arp Shows the local arp cache • Manipulate with arp cache – Add static route To secure system and increase network speed – Flush arp cache If you have stale arp entries – Delete entry in arp cache Remove faulty entries # arp –s 192.168.0.12 00:0B:5F:12:81:00 # arp –d 192.168.0.12 # arp Address HWtype HWaddress Flags Mask Iface router.ing-steen.se ether 00:0B:5F:12:81:00 C eth3 grey.ing-steen.se ether 00:06:5B:1A:84:11 C eth3

16. Telnet & local name resolution • The Telnet command is used to connect to another machine over a TCP/IP network – a connection is established and the user logs on as normal – chkconfig telnet on – telnet is a xinetd demon service: /etc/xinetd.d/telnet $ uname -n a01 $ telnet a02 My RedHat linux server! login: hawkeye password: Welcome to Uncle Sam's wonderful world of Unix Remember the bar never closes! $ uname -n a02 • Local name resolution is in /etc/hosts # cat /etc/hosts 127.0.0.1 192.168.0.1 192.168.0.2 192.168.0.3 192.168.0.4 192.168.0.5 192.168.0.6 localhost.localdomain a01.my-site.com a02.my-site.com a03.my-site.com a04.my-site.com a05.my-site.com a06.my-site.com localhost # This host IP address! # Other important hosts a01 a01 a02 a03 a04 a05 a06

17. SSH • The SSH command is used to connect to another machine over a TCP/IP network – a connection is established and the user logs on as normal – chkconfig - -add ssh implements ssh – ssh config sit in: /etc/ssh and run as stand alone server $ hostname a02 $ chkconfig -–list sshd sshd 0:off 1:on 2:on 3:on 4:on 5:on 6:off $ ssh –l peter a01 password: $ hostname a01 – ssh is standard in RedHat 9

18. File Transfer Protocol • FTP is an interactive utility for network file transfer – login to remote host supplying username and password – Client/Server concept • Restrict FTP access using /etc/vsftpd/vsftpd.ftpusers file – FTP access is denied to users named in this file $ ftp a01 Connected to a01 Name (a01:hawkeye): Password: ftp> get file2 ...data about the transfer... ftp> put /etc/hosts /tmp/mash.hosts ...data about the transfer... ftp> bye • Configure vsftpd using /etc/vsftpd/vsftpd.conf file • Two kinds of ftp servers: private ftp and anonymous ftp

19. File Transfer Protocol

20. Berkeley R Utilities & the new S Utilities • The Unix (or Berkeley) r utilities provide an alternative to IP facilities telnet and ftp. • Three programs: rlogin hostname rsh hostname command rcp [host:]file [host:]file scp user1@host:file user2@host:file ssh hostname rdist • For R family: passwords not required if .rhosts files configured – friendly hosts defined for all normal users in /etc/hosts.equiv – users may add to this list in $HOME/.rhosts • For S family: you need to exchange keys (RedHat 9+ default) – Users may add friendly hosts in $HOME/.ssh/authorized_keys – Keys must be give to you from remote host $HOME/.ssh/id_rsa.pub – Keys generated with ssh-keygen –t rsa remote login remote command remote copy, from to secure copy, from to remote command remote distrubtuion

21. Exercise - Who has Remote Access • Here are three files from mash4077 # more /etc/hosts.equiv seoul # more /.rhosts rosies # /home/hawkeye/.rhosts rosies swamp division bfpierce • Can root on seoul copy files to/from mash4077? • Can hawkeye on seoul run commands on mash4077? • Can hawkeye on rosies run commands on mash4077? • Can root on mash4077 copy files to/from rosies? • Can bfpierce on division copy files to mash4077? • Can root on seoul login to mash4077?

22. Remote shells • The rsh (remsh) command – run a command on a named host – standard I/O can be redirected as normal – /etc/profile and .profile not executed – requires /etc/hosts.equiv or $HOME/ .rhosts file to be configured From a02 or a03 you issue the commands below: $ whoami trapper $ rsh a01 ls -l ..run ls –l as trapper on a01 output.. $ rsh a01 ls -l > list.a01 file list.a01 created on local system $ rsh a01 ...same as rlogin... $ rsh –l hawkeye a01 ...same as rlogin –l hawkeye...

23. Remote distribution -rdist • The rdist command – replicating/maintain identical copies of files over multiple hosts – relies on rlogin and rsh – can use ssh as transport for secure mode – rdist is client software and rdistd is server software – the server rdistd is started via rsh or ssh on the server – R-family rsh requires: /etc/hosts.equiv or $HOME/ .rhosts file to be configured – S-family ssh requires: $HOME/.ssh/rsa_key.pub to be copied from remote server/client – Uses a special file Distfile for updating and maintaining files – Can syslog to /var/log/messages file RDIST HOME: http://www.magnicomp.com/rdist/ • The rdist command is RedHat standard

24. Remote distribution –preparation Pepare a master-server and a client files to replicate 1. Logins must be done without password on clients, or rdist fails. 2. With R-Family: setup server and clients like on page 22 in this chapter. 3. With S-Family: Generate keys and distribute server keys to all clients, look below. 4. S-Family: Enable ssh root-logins on all clients. 5. Create a Distfile with files and directories to update on your clients with. Enable root logins (trusted enviroment only) on all clients: 1. sshd config file: /etc/ssh/sshd_config: PermitRootLogin yes AuthorizedKeysFile .ssh/authorized_keys • •

25. Remote distribution –preparation test Generate server private and public keys: 1. As root generate server keys on server: # ssh-keygen –t rsa 2. Copy keys to identity files: # cd .ssh ; cp id_rsa identity ; cp id_rsa.pub identity.pub Distribute public keys to clients: 1. Create client private and public keys: # ssh <client ip> ssk # ssh <client ip> ssk- -keygen keygen – –t rsa 2. Distribute server public key to all your clients (they need /root/.ssh catalog): # scp identity.pub <client ip>:.ssh/authorized_keys # scp identity.pub <client ip>:.ssh/authorized_keys As root on the server, test root password-less login rights to all of the nodes/clients by: # # ssh node01 date sat dec 12 14:52:55 CET 2004 • • t rsa •

26. Remote distribution -Distfile • Used to specify how replication should take place • The Distfile format: <variable name> `=' <name list> [ label: ] <source list> `->' <destination list> <command list> [ label: ] <source list> `::' <time_stamp file> <command list> The label is optional. HOSTS is in our example all hosts and logins that FILES can be replicated to/from ${FILES} -> ${HOSTS} sends files to list of hosts. /usr/src/bin -> arpa sends catalog with contents to host arpa Commands list is instrcution howto install/operate with lists/files

27. Remote distribution –execute rdist Create some testfiles to distribute among clients. # vi /etc/my-rdist-testfile This is the rdist test file! Create a Distfile • • NODES = ( a01 a02 a03 a04 ) ETCFILES = ( /etc/my-rdist-testfile ) ${ETCFILES} -> ${NODES} install; This file willl replicate the ETCFILES onto all the NODES. Replicate the files using rdist together with SSH • # /usr/local/bin/rdist -P /usr/local/bin/ssh -p /usr/local/bin/rdistd -f /etc/Distfile You may want to run this command every night on your master-server by using the crontab command.

28. Internetwork demon Configuration • Internet facilities controlled by the internet daemon – /usr/sbin/xinetd – started up from /etc/inittab • xinetd controlled by configuration file /etc/xinetd.conf – Tells where facilities/service catalog sit – Set mandatory facility/service configuration and logging – Former name was inetd.conf and inetd demon • Services configuration files /etc/xinetd.d/ Telnet example: service telnet { disable = no flags = REUSE socket_type = stream wait = no user = root server = /usr/sbin/in.telnetd log_on_failure += USERID }

29. Summary • Unix systems use TCP/IP for networking • Every host on the network must have a unique IP address • The file /etc/hosts maps names into IP addresses for network utilities • Systems using DNS don't keep local host files • Unix supports standard TCP/IP programs such as ping, telnet and ftp • Unix provides its own equivalents (rlogin, rcp/scp, rsh and rdist) which use .rhosts files • Unix uses several TCP/IP configuration files in /etc (xinetd.conf, services, etc.)