CCNP Route FAQ: Managing Scalable Network Growth

Answer: The following are reasons to use an IP tunnel:

• To solve problems with discontiguous networks
• To simplify network administration
• To tunnel desktop protocols through an IP-only backbone

Answer: Access lists may be used for the following:

• Queuing
• Policy routing
• QoS
• Filtering routing updates

Answer: By default, only one tunnel is allowed with the same source and destination address.

Answer: By matching the numbers in the following list you will have the correct answers:

Network Congestion	Problem IOS Solution
Clients cannot connect to the centralized servers	3. Routing access list
Cisco environment in a large network with a large number of WAN connections	5. Prioritization on the interface
Large routing tables using RIP for IP	4. Reduction of the size of the broadcast domain by adding a router
Spanning tree is failing	1. IP helper address
SNA sessions are failing	2. EIGRP

Answer: The command that would prevent the router from forwarding data to a remote network without generating an ICMP message is the interface null 0 command.

Answer: Two commands that might be used to verify the configuration of an IP access list configuration could be taken from the following list:

• show ip interface
• show access-list
• show running config
• show startup config

Answer: UDP ports that the IP helper address will forward automatically are TFTP, DNS, BOOTP server, BOOTP client, time, TACACS, NetBIOS name server, and NetBIOS datagram service.

Answer: As the number of workstations increases on a physical segment, the user may experience delays because of the following reasons:

• There are collisions that require retransmission.
• There is packet loss because buffers on devices are overflowing and require retransmission.
• The end systems could be slowing down because of excessive broadcast traffic.

Answer: You should consider at least three of the following:

• Minimize the distance that denied traffic must travel. Place the access list as close to the source as possible.
• Keep the denied traffic off the backbone connecting buildings or campuses.
• Ensure that the router chosen can deal easily with the additional CPU requirements.
• Consider the CPU utilization because an inbound access list does not have to do a routing update on denied traffic.
• However, the interface may have to match the access list against more traffic.
• Consider the number of interfaces affected.
• Consider the number of nodes affected. Outbound access lists may afford greater granularity.
  Consider access list management.
• Consider the network growth and the effect on the management of the interfaces and the changing needs in connectivity.

Answer: The function of the access layer is to act as the first point of contact for the end devices or workstations. It also acts as a filter layer to ensure that all local traffic stays local and does not unnecessarily clog the network.

Answer: The extended access list number range is 100 to 199.

Answer: Priority queuing enables network managers to define how they want traffic to be prioritized in the network. By defining a series of filters based on packet characteristics, traffic is placed into a number of queues; the queue with the highest priority is serviced first, and then the lower queues are serviced in sequence. If the highest-priority queue is always full, this queue will continually be serviced, and packets from the other queues will queue up and be dropped. In this queuing algorithm, one particular kind of network traffic can dominate all others. Priority queuing assigns traffic to one of four queues: high, medium, normal, and low.

Answer: Symptoms of network congestion include these:

• Applications timing out at end stations
• Clients not being capable of connecting to network resources
• Network death resulting

The causes of congestion are often the symptoms seen, and they include these:

• Excessive traffic, seen on the network-management tools
• Dropped packets, seen on the router interfaces
• The retransmission of packets, seen on the network-management tools
• Incomplete routing tables, seen on the router
• Incomplete service tables, seen on servers and routers
• Broadcast storms caused by spanning tree

Answer: If the Spanning-Tree Protocol fails to see the BPDU packet in time, it will unblock the redundant path, in the belief that the primary path is no longer available.

Answer: The dropping of packets could increase the traffic on the network because the applications may request the retransmission of the packet. This is particularly true on a connection-orientated communication.

Answer: Services may be lost when network congestion is experienced. The reasons include these:

• The input buffers of the server are overloaded.
• The application times out.
• The network traffic informing clients of services is lost or delayed sufficiently for the services to be dropped from the
• server lists.

Answer: A layer is created by defining what needs to run through the layer. The core layer is defined by the need for a high-speed backbone linking the different sites, or logical groupings, of the network. It is the central internetwork for the entire enterprise and may include LAN and WAN backbones. The primary function of this layer is to provide an optimized and reliable transport structure.

Answer: The access layer is the layer that is the closest to the end stations. The router keeps that local traffic local and therefore prevents unnecessary traffic from traversing the network. The access layer is designed to ensure that LAN traffic can be contained locally and does not travel off the network to create network congestion.

Answer: Access lists are not recommended at the core layer because this is where the traffic should switch at the highest speeds. Because access lists are CPU-intensive (adding about 15 percent overhead), they are not recommended for use in the core layer. This is still true despite the fact that the technology allows the access list to be cached for fast switching; the general rule is that all decisions are made at the previous layers of the network.

Answer: The distribution layer provides the demarcation point between the core and access layers, providing policy-based connectivity and allowing you to do packet manipulation.

Answer: The packet from an inbound access list will not be sent to the routing process if a match is found for the access list criteria, and the action is to deny the packet. The packet is discarded before it reaches the routing process.

Answer: The following are all valid uses for access lists:

• Restricting networks sent out in routing updates
• Restricting connectivity to remote networks
• Restricting the services advertised in an IPX network
• Restricting large packet sizes from traversing the network

Answer: The default wildcard mask in an IP standard access list is 0.0.0.0.

Answer: If the packet being tested against the access list does not match any of the criteria, it will hit the implicit deny all at the bottom of the access list. This results in it being discarded, generating an ICMP message to the sending station.

Answer: The null interface does not report an ICMP message because there is no error to report. From the viewpoint of the routing process, the packet has been successfully routed to the outgoing interface. The routing process is unaware that the outgoing interface is a virtual interface that does not exist. Effectively, the packet has been sent to the dump, thus killing the packet.

Answer: To restrict Telnet connections into the router that you are configuring, use access lists that are applied to the terminal lines with the access-class command.

Answer: The queuing techniques manually configured on a Cisco system are custom and priority queuing.

Answer: ip helper address is a command that has the router forward User Datagram Protocol (UDP) broadcasts received on an interface to a directed or specific destination on another network.

Combined with the ip forward-protocol global configuration command, the ip helper-address command enables you to control which broadcast packets and which protocols are forwarded. One common application that requires helper addresses is Dynamic Host Configuration Protocol (DHCP). DHCP is defined in RFC 1531. DHCP protocol information is carried inside BOOTP packets. To enable BOOTP broadcast forwarding for a set of clients, configure a helper address on the router interface closest to the client. The helper address should specify the address of the DHCP server. If you have multiple servers, you can configure one helper address for each server. Because BOOTP packets are forwarded by default, the router can now forward DHCP information. The DHCP server now receives broadcasts from the DHCP clients.