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Communication Between
Networks
How the Internet Got Its Name
Addressing to get Out of Town
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MAC Addresses used for Local Traffic
Hierarchical Addressing Needed for internetwork traffic. (Think Zip Codes or Phone #).
Network Layer Protocols:
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IP: Early 1980s, ARPANet, used with TCP
IPX: Late 1980s to 90s. 32-bits for network + MAC
Routing Layer in DECnet: 1975 –
Path Control Layer in SNA
Internet Protocol Version 4 (IPv4)
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What’s in a Name?
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All Internet Names (i.e. alllinksvt.com) convert IP
Address (using Domain Name Service)
32-bit address, divided into 4 8-bit sections
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A.B.C.D (i.e. 68.178.232.99)
Numbers can be between 0 and 255 (8-bits)
Part of the address identifies the Network, the
other part identifies the host.
Networks and Hosts
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IP Network Addresses are assigned using IP
Address and Subnet mask.
Subnet mask defines network and host portions.
Example:
IP Addr
10
24
250
12
Netmask
255
255
0
O
Network
10
24
0
0
0
0
250
12
Host
Special IP Addresses
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Private IP Addresses:
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Do not Route on Internet
10.0.0.0/8 (i.e. netmask=255.0.0.0)
172.16-32.0.0/16 (i.e. netmask=255.255.0.0)
192.168.x.x/24 (i.e. netmask=255.255.255.0)
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These Addresses are used on LANS.
Routers translate these to routable IP Addresses
using Network Address Translation
Without Private Address we would be out of IP Addr.
Network Address Translation
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Router translates internal (private) address to
external (public) IP Address.
Typically this is a many to one translation.
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All external communication uses Routers WAN
Address.
Router keeps a table of connections in order to
route correctly.
Helps security by obscuring LAN IP Addresses
You can’t attack what you can’t see.
Where do IP Addresses Come From?
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Globally: Internet Assigned Numbers Authority
(IANA)
Regional:
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American Registry for Internet Numbers (ARIN) for North
America and parts of the Caribbean
RIPE Network Coordination Centre (RIPE NCC) for
Europe, the Middle East and Central Asia
Asia-Pacific Network Information Centre (APNIC) for Asia
and the Pacific region
Latin American and Caribbean Internet Addresses Registry
(LACNIC) for Latin America and parts of the Caribbean
region
African Network Information Centre (AfriNIC) for Africa
Configuring IP Addresses
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Can be Set Manually
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IP Address
Subnet Mask
Default Gateway
DNS 1, DNS2
Can be set by Dynamic Host Configuration
Protocol Server.
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A range of LAN addresses is set aside
DHCP Server “Leases” these out.
Host-Based Routing Decision
Routers: Getting There from Here
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Hop by Hop Routing
Routers Build Routing Tables
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Network ID
Cost
Next Hop
Quality of Service
Filtering
Interface
Routed vs Routing Protocols
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Routed Protocols are protocols that get
routed.
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Web
E-mail
IPX
Routing Protocols define how and what
routers share
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Routing Information Protocol (RIP)
Open Shortest Path First (OSP)
Cisco Proprietary: IGRP, EIGRP, BRP
What do Routers Do?
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Operational
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Forward Packets towards destination
Access Control (Firewall Functions)
Types of Routes
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Static: non-adaptive, created manually.
Distance-Vector RP: Cost calculated for each path
Link-State: creates a (flood) map of network
Path-Vector Protocol: Good for large inter-domain
routing
Routing Table