VPN and IP Multicast in Network Layer: Concepts, Tech, and Optimizations, Slides of Computer Networks

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4: Network Layer 4a-

IP Extensions – VPN, Mobile

IP, IP Multicast

4: Network Layer 4a-

Virtual Private Networks (VPN)

4: Network Layer 4a-

How accomplished?

 IP encapsulation and tunneling

 Router at one end of tunnel places private

IP packets into the data field of new IP

packets (could be encrypted first for

security) which are unicast to the other

end of the tunnel

4: Network Layer 4a-

Tunneling

IPv6 inside IPv4 where needed

4: Network Layer 4a-

Examples

 Logical Network Creation

 Virtual Dial-Up

4: Network Layer 4a-

Logical Network Creation

Example

 Remote networks 1 and 2 create a logical

network

 Secure communication at lowest level

Internet

Gateway (^) Tunnel Gateway

Network 1

Network 2

4: Network Layer 4a-

MobileIP

4: Network Layer 4a-

MobileIP

 Goal: Allow machines to roam around and

maintain IP connectivity

 Problem: IP addresses => location

 This is important for efficient routing

 Solutions?

 DHCP?

• ok for relocation but not for ongoing connections

 Dynamic DNS (mobile nodes update name to IP

address mapping as they move around)?

• ok for relocation but not for ongoing connections

4: Network Layer 4a-

MobileIP

 Mobile nodes have a permanent home

address and a default local router called

the “home agent”

 The router nearest a nodes current

location is called the “foreign agent”

 Register with foreign agent when connect to

network

 Located much like the DHCP server

4: Network Layer 4a-

Forwarding Packets

 Home agent impersonates the mobile host

by changing the mapping from IP address

to hardware address (“proxy ARP”)

 Sends any packets destined for mobile

host on to the foreign agent with IP

encapsulation

 Foreign agent strips off and does a special

translation of the mobile nodes IP address

to its current hardware address

4: Network Layer 4a-

Avoiding the Foreign Agent

 Mobile host can also obtain a new IP

address on the remote network and inform

the home agent

 The home agent can then resend the

packet to the new IP address

4: Network Layer 4a-

Optimizations

 What if two remote hosts are temporarily

close together

 If they want to send traffic to each other,

why should it have to go all the way to

their home agents and back again

 Optimizations exist to allow the sending

node to learn and cache the current

location of a recipient to avoid this

problem

4: Network Layer 4a-

What is multicast?

 1 to N communication

 Bandwidth-conserving technology that

reduces traffic by simultaneously

delivering a single stream of information to

multiple recipients

 Examples of Multicast

 Network hardware efficiently supports

multicast transport

• Example: Ethernet allows one packet to be received by many hosts

 Many different protocols and service models

• Examples: IETF IP Multicast, ATM Multipoint

4: Network Layer 4a-

Unicast

R

 Problem Sender

 Sending same data to

many receivers via

unicast is inefficient

 Example

 Popular WWW sites

become serious

bottlenecks

 Especially bad for

audio/video streams