Ip Forwarding Architectures

High-performance forwarder

High-performance forwarder

(1) Pure destination-based forwarding (lookup based on IP address)

(2) Switched forwarding

(a) Overlay model (b) Peer model

(2) Switched forwarding

(a) Overlay model (b) Peer model

FIGURE 10.1 IP forwarding taxonomy typically required implementation in software or firmware. Category 2 can be further classified into the overlay model and the peer model.

In the overlay model, ATM switches are not aware of IP addresses and IP routing protocols. This model overlays an IP network onto an ATM network, essentially creating two network infrastructures with two addressing schemes and two routing protocols. Each end system uses both IP and ATM addresses that are uncoupled. Thus an address resolution protocol is required to map from one address to another. One advantage of this model is that the ATM infrastructure can be developed independently of the IP infrastructure. Examples of this model are classical IP over ATM and multiprotocol over ATM.

The peer model uses the existing IP addresses (or algorithmically derived ATM addresses) to identify end systems and uses IP routing protocols to set up ATM connections. One advantage of the peer model is that it does not require an address resolution protocol to interwork routeable address spaces and thus simplifies address administration. A node typically has an integrated ATM switching and IP routing function, and the node can be viewed as a "peer" to other routers. The peer model maintains one network infrastructure. The best example of this model is multiprotocol label switching.

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