Communication Between Networks

How the Internet Got Its Name

Addressing to get Out of Town MAC Addresses used for Local Traffic Hierarchical Addressing Needed for inter-

network traffic. (Think Zip Codes or Phone #). Network Layer Protocols:

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) What’s in a Name?

All Internet Names (i.e. alllinksvt.com) convert IP Address (using Domain Name Service)

32-bit address, divided into 4 8-bit sections 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 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

Host 0 0 250 12

Special IP Addresses

Private IP Addresses: 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) 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

Router translates internal (private) address to external (public) IP Address.

Typically this is a many to one translation. 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? Globally: Internet Assigned Numbers Authority

(IANA) Regional:

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

Can be Set Manually IP Address Subnet Mask Default Gateway DNS 1, DNS2

Can be set by Dynamic Host Configuration Protocol Server. A range of LAN addresses is set aside DHCP Server “Leases” these out.

Host-Based Routing Decision

Routers: Getting There from Here Hop by Hop Routing Routers Build Routing Tables

Network ID Cost Next Hop Quality of Service Filtering Interface

Routed vs Routing Protocols

Routed Protocols are protocols that get routed. Web E-mail IPX

Routing Protocols define how and what routers share Routing Information Protocol (RIP) Open Shortest Path First (OSP) Cisco Proprietary: IGRP, EIGRP, BRP

What do Routers Do?

Operational Forward Packets towards destination Access Control (Firewall Functions)

Types of Routes 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