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Internetworking

Sub-topic Outline:

• Different types of Internetworking
• Concatenating Virtual Circuits
• Datagram Internetworking
• Tunneling
• Internetwork Routing
• Firewalls

Internetworking

• Many different networks with different protocols exist and will probably continue to exist.
• To connect different networks, we need a "box" existing between the networks to convert the data.
• What the "boxes" are called depends on what level they deal with the data.

Different Approaches Internetworking

1. Concatenating Virtual Circuits
2. Datagram internetworking
3. Tunneling

Concatenating Virtual Circuits

• Construct VCs through all the intermediate networks
• Appropriate only when the different networks have similar properties (eg. reliable service, connection-based etc)
• The steps taken to construct the VC joining one gateway to another is as normal - but now also construct a VC joining all the gateways.

Datagram Internetworking

• Again, extended from the idea of datagrams on one network - but the packets have to be converted by the gateways.
• Problems:
  • The formats of the packets must be similar enough to convert.
  • Addressing - the intermediate network may not support the address format of the final destination.

Comparing VC with Datagram Internetworking

• VCs:
• Can reserve buffers at gateways
• Guaranteed sequencing and flow
• Short packet headers
• Require table space at gateways
• Hard to adapt to congestions
• Vulnerable to gateway failure
• Can't implement if one intermediate network is datagram-based.
• Datagrams:
• Potential to adapt to congestion
• Respond to gateway failures
• Can be implemented over VC or datagram-based networks.
• Larger packets.
• More traffic

Tunneling

• Applicable to both VC and Datagram internetworking.
• Avoids the problems of incompatible header formats between networks.

Without Tunneling:

With Tunneling:

Internetwork Routing

• Can use the routing algorithms we have already studied, by coming with a topology for the gateway connections.
• We ignore the routing with each individual network, and assume they are done independently
• Some extra considerations:
• Internetworking usually cross international boundaries, and different laws (eg. on privacy) have to be considered
• Price for charges different

Firewalls

• One major consideration for gateways is security:
• What packets to let into a network? Potential viruses, worms, etc.
• What packets to let out of a network? Potential unauthorized access.
• A firewall is a gateway which filters all incoming and outgoing traffic to/from a network.
• Packet filters operates on the network layer - eg. checks addresses to see if where the packets are coming from.
• Application Gateways operates on the transport and application layer - eg. checks email messages for their size.

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