TDC365 Spring 2001John Kristoff - DePaul University1 Interconnection Technologies Routing I

TDC365 Spring 2001John Kristoff - DePaul University2 Will layer 2 networking suffice?

TDC365 Spring 2001John Kristoff - DePaul University3 Layer 3 usually provides • Internetworking for data link technologies • Globally unique addresses • Scalable routing • A common communications format • Packet fragmentation capability • A hardware independent interface • Packet independence

TDC365 Spring 2001John Kristoff - DePaul University4 Routers • Typically a special purpose, dedicated device • Connects heterogenous networks • Directs packets towards ultimate destination • Dynamic routing algorithsm often used • Make automatic forwarding decisions • Can forward based on various metrics • Also called a gateway • Offical pronounciation is really rooter

TDC365 Spring 2001John Kristoff - DePaul University5 Routing • Scope • Autonomous system, interior, exterior • Dynamic routing • Protocol for route exchange and computation • Static routing • Manually configured routes • Destination address driven

TDC365 Spring 2001John Kristoff - DePaul University6 Internet protocol (IP) • Standardized in RFC 791 • Connectionless • Unreliable • Fairly simple • The Internet Glue

TDC365 Spring 2001John Kristoff - DePaul University7 IP addresses • Virtual – not bound to hardware • 32-bit fixed size • Unique address for each IP interface • Global authories assign a prefix (network) • Local administrators assign the suffix (host) • Usually written as dotted decimal notation • e.g

TDC365 Spring 2001John Kristoff - DePaul University8 Classful IP addressing

TDC365 Spring 2001John Kristoff - DePaul University9 IP address notation

TDC365 Spring 2001John Kristoff - DePaul University10 Classful address sizes

TDC365 Spring 2001John Kristoff - DePaul University11 Limitations of classful addressing • Internet growth • Route table size • Address depletion • Misappropriation of addresses • Lack of support for different sized networks • Class B too big, class C too small

TDC365 Spring 2001John Kristoff - DePaul University12 IP addressing solutions • Subnetting • Supernetting • Classless interdomain routing (CIDR) • Variable length subnet masks (VLSM)

TDC365 Spring 2001John Kristoff - DePaul University13 Subnetting

TDC365 Spring 2001John Kristoff - DePaul University14 Subnet mask • The bit length of the prefix (network) • Prefix (network) is no longer classful • Dotted decimal or '/' notation • 's subnet mask is •...or /25 • You may want to convert to binary for clarify • A /25 or subnet mask is: •

TDC365 Spring 2001John Kristoff - DePaul University15 Supernetting • Combine smaller blocks into larger aggregate • If class B too big, class C too small... • Maybe do this: • Combine /24 to /24 • Equals /20

TDC365 Spring 2001John Kristoff - DePaul University16 CIDR • Use supernetting for routing tables • Routes advertised as smaller CIDR blocks • So instead of advertising: • /24, /24, /24 and /24 separately • Advertise: • /22 one time • Internet CIDR report •

TDC365 Spring 2001John Kristoff - DePaul University17 VLSM • Multiple subnet sizes in a single AS • Allows efficient use of address space • Can be used to build internal hierarchy • External view of AS does not change • An organization may have /16 • But internally may use /17, /24, /24 and so on.

TDC365 Spring 2001John Kristoff - DePaul University18 Special IP addresses

TDC365 Spring 2001John Kristoff - DePaul University19 Obtaining IP addresses • IANA has global authority for assignment • Regional registries delegate (ARIN/RIPE/APNIC) • ISPs assign addresses to end end users • RFC 1918 defines private address netblocks • NOT globally unique • Must not appear on the public Internet • /8, /12, /16

TDC365 Spring 2001John Kristoff - DePaul University20 IP networking example

TDC365 Spring 2001John Kristoff - DePaul University21 IP router addressing example

TDC365 Spring 2001John Kristoff - DePaul University22 IP datagram layout

TDC365 Spring 2001John Kristoff - DePaul University23 Final thoughts • IP is unreliable • IP addressing can be a pain • IPv6 doesn't make it any easier • IP address is both a who and a where • IP addresses provide little security • Private IPs and NAT are best avoided