1 tcp/ip networking yue cui 06/13/02. 2 presentation outline introduction packets and encapsulation...
TRANSCRIPT
2
Presentation Outline Introduction Packets and Encapsulation IP Addresses, Routing ARP, DHCP and PPP Security Issue Addition of Machines
3
Introduction TCP/IP and the Internet
A brief history ARPARNET(1969 by DARPA)
Internet Management ICANN IETF ISOC
Standards and Documentation RFCs, FYIs, STDs and BCPs
4
Introduction TCP/IP protocol suite
IP – routes data packets from one machine to another
ICMP – provides lower-level support for IP, including error messages, routing assistance and debugging help
ARP – translates IP address to hardware address (a.k.a. MAC address)
UDP and TCP – deliver data to specific applications on the destination machine
6
Presentation Outline Introduction Packets and Encapsulation IP Addresses, Routing ARP, DHCP and PPP Security Issue Addition of Machines
7
Packets and Encapsulation Packet
Header—tells where the packet came from and where it’s going
Payload—actual data to be transferred
8
Encapsulation
Layer
5
4
3
2
1
M
H4 M
H4
H4
H3
H3H2
M
M
M
H4 M
H4
H4
H3
H3H2
M
M
source machine
destination
machine
9
Presentation Outline Introduction Packets and Encapsulation IP Addresses, Routing ARP, DHCP and PPP Security Issue Addition of Machines
10
IP Addresses Historical Internet address classes
IP addresses were grouped into “classes” Class A,B and C denote regular IP
addresses. Class D and E are used for multicasting and research purpose.
Subnet masks Part of the host portion of an address is
“borrowed” to extend the network portion. Use ifconfig command to configure IP
address and subnet masks
11
IP Addresses IP address crisis
We were going to run out of class B addresses by mid-1995
The routing tables of Internet backbone sites were growing so large that they would not fit in the memory of available routers
IP addresses were being allocated with no locality of reference
12
IP Addresses Solution to the IP address crisis
CIDR (Classless Inter-Domain Routing) A short-term solution Manage the existing 4-byte address space that
uses the available addresses more efficiently and allows routing tables to be simplified by taking numerical adjacencies into account
IPv6 A long-term solution A revision of the IP protocol that expands the
address space to 16 bytes
13
Routing Meaning
Looking up a network address in the routing table to forward a packet toward its destination
Building the routing table in the first place
Configure netstat route get (on BSD-based system)
14
Presentation Outline Introduction Packets and Encapsulation IP Addresses, Routing ARP, DHCP and PPP Security Issue Addition of Machines
15
ARP, DHCP and PPP ARP: Address Resolution Protocol
Discovers the hardware address(MAC address) associated with a IP address
Usage:Redhat% /sbin/arp –axor.com(192.108.21.1) at 08:00:20:77:5E:A0[ether] on eth0earth.xor.com(192.108.21.180) at 00:50:DA:12:4E:E5[ether]
on eth0
16
ARP, DHCP and PPP DHCP: Dynamic Host Configuration
Protocol Dynamically assigns network parameters to
hosts Leasable parameters include:
IP addresses and netmasks Gateways(default routes) DNS name servers Syslog hosts WINS servers, proxy servers TFTP servers(for loading a boot image)
17
ARP, DHCP and PPP PPP: Point-to-Point Protocol
Serial line encapsulation protocol that specifies how IP packets must be encoded for transmission on a slow serial line
Sometimes used with home technologies such as Dial-up, DSL and cable modem
18
ARP, DHCP and PPP
System Commands Config files
Red Hat /usr/sbin/pppd /etc/ppp/options /usr/sbin/chat /etc/ppp/ppp.conf /etc/ppp/allow
Free BSD /usr/sbin/pppd /etc/ppp/options /usr/sbin/chat /etc/ppp/options.ttyserver /etc/ppp/chat.ttyserver
PPP-related commands and configuration files example
19
Presentation Outline Introduction Packets and Encapsulation IP Addresses, Routing ARP, DHCP and PPP Security Issue Addition of Machines
20
Security Issues IP forwarding ICMP redirects Source routing Broadcast pings and other forms of
directed broadcast UNIX-based firewalls Virtual private networks(VPN) IPSEC: secure IP
(Refer to Chapter 21 for details)
21
Presentation Outline Introduction Packets and Encapsulation IP Addresses, Routing ARP, DHCP and PPP Security Issue Addition of Machines
22
Addition of machines Basic steps
Assign an IP address and hostname Set up the new host to configure its
network interfaces at boot time Set up a default route Point to a DNS name server, to allow
access to the rest of the Internet
23
Assign an IP address and hostname
/etc/hosts file Example from text book127.0.0.1 localhost192.108.21.48 lollipop.xor.com lollipop loghost192.108.21.254 chimchim-gw.xor.com chimchim-gw192.168.21.1 ns.xor.com ns192.225.33.5 licenses.xor.com license-server
hostname command Assigns a hostname to a machine Typically runs at boot time
24
Configure network interface ifconfig command
Common form: ifconfig interface address options…
up/down For example:
Ifconfig en0 128.138.240.1 netmask 255.255.255.0 up
Options Netmask
Sets the subnet mask for the interface Broadcast
Specifies the IP broadcast address for the interface
25
Configure static routes
route command Format:
route [-f] op [type] destination gateway [hop-count]
Options Add, delete, (get, change, flush, monitor)
Default routesroute add default gateway-IP-address
26
Configure DNS
/etc/resolv.conf file All systems require to modify it Sample:
Search cs.colorado.edu colorado.eduNameserver 128.138.242.1Nameserver 128.138.243.151Nameserver 192.108.21.1
27
Configure DNS “service switch” file
Some systems do not use DNS by default, these systems use “service switch” file to resolve hostname-to IP- address mapping
Service switch files by system
System Switch files Default for hostname lookups
Solaris /etc/nsswitch.conf
nis [NOTFOUND=return] files
HP-UX /etc/nsswitch.conf
dns [NOTFOUND=return] nis [NOTFOUND=return] files
Red Hat
/etc/nsswitch.conf/etc/host.conf
db files nisplus dnshosts, bind
FreeBSD
/etc/host.conf host,bind