Network Hardware Lecture 5

Bridging

• Bridging happens at Link layer
• between LANs
• provides
• filtering - only forward packets destined offnet
• repacketization
• speed matching

Routing

• Internetworking (in WANs)
• happens at network layer
• routers connect WANs with very dissimilar characteristics
• also called gateways
• Routing
• routers know whole network topology
• determines which network to send packet on next from destination address
• protocol conversion
• fragmentation
• when packet too large for next network it must pass through

Routing (continued)

Routing (continued)

Internet Futures

• Current IP protocol is running out of addresses
• 32 bits = 4 billion addresses
• Class A - 127 large groups with 16M machines
• countries
• Class B - 16K networks with 64K or fewer machines
• Class C - 2M networks with 256 machines
• each machine can only have one network address
• Revised IP protocols (IPng) currently being devised
• 128 bit addresses
• also called IPv6

• 0

• 0

• 0

• 24

• 0

• 7

• 16

• 14

• 8

• 21

• 28

• 1

• 1

• 1

• 1

• 1

• 1

• A

• B

• C

• Multicast

Web-based Commerce

• Conducting business (exchanging money) over the Internet requires several features that aren’t yet available
• confidentiality
• no one else listens to the transaction
• authentication
• you really are who I think you are
• data integrity
• no one increases my order enroute
• nonrepudiation
• I can’t back out after I buy
• selective application of services
• seller never sees my credit card number
• I seal it and only give name of the bank, who authorizes payment

• encryption

• digital signatures and certificates

Web-based Commerce (continued)

• Public-key systems provide confidentiality
• I choose 2 keys, one public and one private
• publish public key widely
• I encode with private key
• you decode with public key
• you encode with public key
• I decode with private key

• or

Web-based Commerce (continued)

• Digital signatures use public key algorithms, usually on digest of message to speed up
• encode message digest (hash function)
• cleartext message also digested at receiving end
• if my decoded digest matches calculated one, I sent it and it hasn’t been changed

Web-based Commerce (continued)

• Authentication provided by authentication entities
• I don’t send order directly to Nordstroms
• send to authenticator instead, who verifies I’m me and sends the order to a prestored Nordstroms address
• other variations exist
• Several proposals to modify IP protocols at various levels to help this
• IP protocol
• Secure Sockets Layer session protocol
• secure HTTP and MIME messaging