Transcript Digital Security - UC San Diego
Internet Protocol Fundamentals
Gateway to the World
By Eric L. Michelsen
Inductive Logic
Internet Protocol Services Where in the Stack Is IP?
IP Addressing IP Networks and Hosts IP Network Classes Multi-homed hosts Routing Minimum Host Configuration
Topics
Point to Point Links Subnetting Classless Inter-Domain Routing (CIDR) Private Addressing DNS UDP TCP: Reliable Delivery IPv6 (IP, the Next Generation)
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Where in the Stack is IP?
IP is a layer 3 protocol (network layer) IP is designed to run over any and all link layers (layer 2) 4 3 2 1 5 6 7 IP folk used to think of a 4-layer stack OSI Application Telnet, FTP, email, Netware services Presentation Session 4 IP Application Transport Network Link Physical UDP, TCP, Novell SPX IP, IPX, NetBIOS Ethernet II, IEEE 802.2
10Base-T, T1, V.34, EIA-232 3 2 1 Transport Network Physical TCP, UDP IP 11/9/2000
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Internet Protocol Services
IP v4 (RFC-791, and
many
others) IP provides 3 primary Services: • • • Global addressing Best-effort (not guaranteed) datagram delivery Fragmentation Base protocol on which
many
built others are Upper layers provide reliability as needed Fragmentation is inefficient, and generally avoided.
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IP Addressing
32-bit (4-octet) address, written in
dotted decimal
: • w.x.y.z
e.g., 206.71.190.4
w, x, y, and z are octets, ranging from 0 to 255 Each IP address is globally unique • except for private addresses An
IP network
is a group of hosts that can communicate “directly” with each other • “directly” means no intervening IP devices All IP packets include the destination and source IP address
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IP Networks and Hosts
A typical IP network might be an Ethernet: Host 206.71.190.1
Host 206.71.190.2
Host 206.71.190.3
Host 206.71.190.4
206.71.190.0
Each host interface has an IP address An IP address includes two parts: the
network address
, and the
host address
, e.g.
network 206.71.190 .4
host All hosts on net have the same network address The network as a whole is referred to as host = 0 11/9/2000
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Another Sample IP Network
Full-mesh Frame Relay network • Any two hosts can communicate “directly” Broadcasts must be duplicated by sender to each VC Host 206.71.190.2
Host 206.71.190.1
PVC Single IP Interface PVC PVC PVC PVC PVC The whole mesh is network 206.71.190.0
Host 206.71.190.3
PVC Host 206.71.190.4
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Classical Class
Network/host address sizes vary in classes: • Class A: N.h.h.h (0.0.0.0 to 127.0.0.0) 128 networks, 16M hosts per network Example: 10.1.1.1
network 10 , host .1.1.1
• Class B: N.N.h.h (128.0.0.0 to 191.255.0.0) 16,384 networks, 65k hosts per network Example: 132.10.5.17
network 132.10
, host .5.17
• • Class C: N.N.N.h (192.0.0.0 to 223.255.255.0) 2M networks, 254 hosts per network Example: 206.71.190.13
Classes D & E are “special” network 206.71.190
, host .13
Host address of all 1s (e.g., 206.71.190.255) means
broadcast
to an entire IP network (deprecated)
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Multi-homed Host
A host may appear on multiple networks Each network
interface
has an IP address 199.107.10.0
199.107.10.12
multi-homed Host 206.71.183.4
206.71.183.0
A multi-homed host may be used to forward packets between networks (i.e., as a
router
)
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Routing
Connecting networks into an “internetwork” Host 192.168.1.0
Host Host 192.168.20.0
Host 192.168.1.1
Router 206.71.183.1
Host Host 206.71.183.0
192.168.20.1
Router 206.71.183.2
Host Host
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Minimum Host Configuration
2 configuration items required for full internetwork access: • • An IP address A default router Host learns new routes from default router with
redirects
Every host (not just routers) must maintain a routing table 192.168.1.0
192.168.20.0
11/9/2000 192.168.1.1
Router 206.71.183.1
forwarded 1 st packet 206.71.183.0
subsequent packets 192.168.20.1
Router 206.71.183.2
1 st packet to 192.168.1.x
redirect Host IP 206.71.183.9
Default router 206.71.183.2
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Point-to-Point Links
Numbered Link: standard IP (wasteful) • • All hosts must have same network number Wastes a whole network address for 2 hosts Host 206.71.190.1
206.71.190.0
Host 206.71.190.2
Unnumbered Link: efficient • No network number • • Host addresses are completely arbitrary Used almost exclusively on routers, and host PPP links Router 206.71.190.3
unnumbered Router 199.107.183.15
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Subnet Masks
The
subnet mask
defines which parts of an IP address are the ‘network’ and ‘host’ parts 1s in the subnet mask specify network address bits, 0s specify host address bits Standard class subnet masks: • Class A: 255 .0.0.0
11111111.
00000000.00000000.00000000
• Class B: 255.255
.0.0
11111111.11111111
.00000000.00000000
• Class C: 255.255.255
.0
11111111.11111111.11111111
.00000000
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Subnetting
Creates networks smaller than the default for their class (breaks up Class A, B, & C networks) • Example: subnet mask 255.255.255.192 = 11111111.11111111.11111111.11
000000 creates a subnet of 64 addresses (62 hosts) • Can use 255.255.255.0 on an (otherwise) Class B network to create 256 Class-C-size subnets (254 hosts) Network part is always on left end of subnet mask Handy table: 128 192 224 1000 0000 1100 0000 1110 0000 240 248 252 1111 0000 1111 1000 1111 1100 Sometimes written as /
n
, where
n
Network part, e.g., /26 is # bits in => 255.255.255.192
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Examples of IP Subnetting
192.168.1.0
192.168.1.0/24 (mask 255.255.255.0) • standard Class C • 254 hosts: 192.168.1.1 - 192.168.1.254
192.168.1.0/24 192.168.2.0/25 (mask 255.255.255.128) • 126 hosts: 192.168.2.1 - 192.168.2.126
192.168.2.128/26 (mask 255.255.255.192) • 62 hosts: 192.168.2.129 - 192.168.2.190
192.168.2.192/27 (mask 255.255.255.224) • 30 hosts: 192.168.2.193 - 192.168.2.222
192.168.1.255
192.168.2.0
192.168.2.0/25 192.168.2.127
192.168.2.128
192.168.2.128/26 192.168.2.191
192.168.2.192/27
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CIDR
Classless Inter-Domain Routing Eliminates Class A, B, and C networks.
Subnet masks must be specified for everything • This is a 3rd piece of configuration now required by an IP host: IP address Subnet mask Default Router Widely used, and growing
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Private Addresses
IETF set aside some addresses for “private” use: • 1 Class A network • • 16 Class B networks 256 Class C networks 10.0.0.0
172.16.0.0 - 172.31.0.0
192.168.*.0
Internet routers are configured to discard packets addressed to these addresses These addresses are not visible to the Internet, so multiple sites can use them at will
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DNS: Domain Name System
RFCs 1034, 1035 Memorizing IP addresses is difficult DNS is a distributed directory of names, and associated IP addresses, and other info • “First DNS server” is a 4th piece of IP host config Hierarchical system of shared authority • Right parts are higher authority than left www .enterprise.com
Enterprise Administered InterNIC Administered
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UDP: User Datagram Protocol
RFC 768 Built above IP (Layer 4, Transport) Best-effort, datagram (packet) delivery (
connectionless
) Adds an additional addressing layer:
port
• Each UDP datagram includes a 16-bit destination and 16-bit source port • There are many “well-known” ports, which essentially act as Server IDs or Protocol IDs for UDP DNS BOOTP/DHCP TFTP SNMP port 53 ports 67 (server), 68 (client) port 69 port 161 11/9/2000
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TCP: Transmission Control Protocol
RFC 793, plus many modifications Reliable, error-corrected
stream
of data Connection oriented (has setup and teardown) Uses a highly efficient, self-adjusting pacing mechanism for high throughput No packetization (or frame) boundaries • Packetization of data stream into IP packets is invisible to the application layer Packet boundaries (if needed) must be created by higher layers Like UDP, has
ports
. Well known ports: FTP control Telnet SMTP port 20 port 23 port 25
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IPv6 (IPng)
Primarily intended to address the problem of running out of IP addresses Aka Network Engineer Employment Act of 1994 • • Nearly every IP protocol must change Nearly every IP software application must change Addresses extended to 16 octets (128 bits) • Enough for each molecule on the surface of the earth to have its own IP address Part of address is locally assigned Fragmentation confined to endpoints (routers don’t fragment, hosts do)
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