Understanding the network.pdf - Back to Home

traffic flow management issues that ATM was developed to address,
but are effectively lost when utilized with traditional connectionless
Layer 3 protocols. Cisco's Tag Switching and MPLS efforts are not
specific to ATM. They are instead a technology bridge that will be used
between traditional connectionless IP networks and the public
connection-oriented ATM. This adaptation will more than likely
comprise most of the Internet and private networking backbones in
the near future.
With MPLS packets, routing decisions are not made in the traditional
manner. Instead, the first router (normally the edge router between
the LAN and the Internet or private data network) decides the route
the packet will take to reach its destination. This packet forwarding
information is appended as a label, either within the Layer 2 packet
header (if natively supported) or appended to the actual packet
between the Layer 2 and Layer 3 headers. This label is then used by
MPLS-supported routers to perform destination-based routing.
Packets are forwarded between other MPLS routers based on
comparisons between the packet's label and the MPLS router's
Forwarding Information Base (FIB). FIB is generated by information
learned from traditional dynamic routing protocols such as OSPF and
BGP. After the packet leaves the MPLS cloud, the label is removed and
the packet is handled by traditional means.
The advantage of MPLS is that it is a software-based mechanism that
can work with most existing networking hardware and Layer 3
protocol technologies.
Summary
In this chapter, we covered a myriad of essential material dealing with
the operation and implementation of LAN and ATM network switches.
The material provided in this chapter offered an overview of the many
topics discussed. You are encouraged to read additional material on
these subjects. The following is a list of topics you should understand
by the end of this chapter:
• The foundations of switch operations
• Transparent, translation, encapsulation, and source route
bridging
• The spanning tree algorithm
• LAN and ATM switch architectures
• A comparison of bridge and router operation
• LANE and Classical IP over ATM, and MPLS