You have seen the major tasks that must be performed when managing a complex internetwork.
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A hierarchical design divides internetworks into three logical services:

  • backbone

  • distribution

  • local area access

To identify a complex internetwork, you look for 
the following characteristics:

  • more than 500 routes

  • global topology with multiple remote connections

  • emphasis on security

  • routed and non-routed traffic on the same 
    medium

Network congestion occurs when the amount of 
data to be transmitted by a particular medium 
exceeds the bandwidth of the medium.

To resolve congestion, the traffic must either 
be reduced or rescheduled.

You can control network congestion by

  • filtering traffic

  • prioritizing traffic with queues

  • limiting broadcast/multicast traffic
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You have seen how to configure standard IP access lists on a Cisco router.
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An access list is a sequential collection of permit and deny conditions that apply to IP addresses.

You use access lists to permit or deny packets from crossing specified interfaces.

You define a standard access list using the Access-List command in global configuration mode.

The syntax of the command is

  access-list £Baccess-list-number£b {permit|deny}
     {source[£Bsource-wildcard£b]|any}

You use the IP Access-Group command in interface configuration mode to link an existing access list to an interface.

The syntax of the command is

  ip access-group £Baccess-list-number£b {in|out}
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You have seen how to configure extended IP access lists on Cisco routers.
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Extended access lists provide a higher degree of control than standard access lists.

You can use extended access lists to enable filtering based on

  • protocol

  • source or destination address

  • application port number
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You have seen how the different Cisco IOS queuing strategies operate.
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Queuing is a mechanism that prioritizes one type of network traffic over other types.

This is done by reordering the packets that constitute the traffic.

You use priority queuing to prioritize datagrams traveling on an interface.

Packets are classified according to various criteria, including protocol and subprotocol type.

They are then queued on one of four output queues

  • high

  • medium

  • normal

  • low

Custom queuing assigns different amounts of queue space to each protocol and handles the queues in round-robin fashion.

A particular protocol may be prioritized by assigning it more queue space, but it will never monopolize the entire bandwidth, so there is no risk of lower priority packets being lost.

Cisco's implementation of weighted fair queuing divides traffic into conversations based on packet header addressing.

A queuing weight is assigned to each conversation based on bandwidth requirements and other variables.

A conversation index determines whether traffic represents low-volume or high-volume conversations.

The switching logic within the Cisco IOS determines the selection of the data path through the router.
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Cisco IOS 11.1 provides functionality to allow selective forwarding of broadcast packets on an interface.
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Cisco IOS 11.1 supports directed and flooded 
broadcasting, and can be configured to generate 
any form of IP broadcast address.

By default, routers offer protection against 
broadcast storms, whereas bridges propagate them.

Flooding of broadcast packets can be done in a controlled manner using a spanning tree of the network.

Helper addresses allow a router or series of routers to relay broadcasts that would otherwise be blocked.

Cisco IOS 11.1 supports multiple helper addresses 
on each interface so that broadcast packets can be 
forwarded to multiple hosts.

User Datagram Protocol (UDP) and Network Disk (ND) forwarding are enabled by default on any interface configured with a helper address.
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