Implementing Redistribution & Controlling Routing Updates

1) State two of the methods that Cisco recommends for controlling routing protocol traffic.

** The methods that Cisco discusses as useful methods of controlling routing updates are as follows:
- Passive interfaces: Prevent routing protocol communication and thus an adjacency from being formed with neighboring routers.
- Changing the administrative distance on the route: Changes the natural order as laid down by Cisco on which routing protocol is more plausible than the others. A scale of weighting is applied to the protocols.
- Default routes: Instruct the router on where to send the destination traffic if the routing table has no entry for that destination.
- Static routes: Offers the ability to configure manually the path to a destination network.
- Route update filtering: Offers the use of access lists to control the exchange of routing information

2) What is the default administrative distance for RIP?

* * The administrative distance for RIP is 120; it has the highest distance of interior routing protocols and is therefore the least likely to be selected.

3) State two instances when you do not want routing information propagated.

** The two occasions that you do not want routing information to be propagated are as follows:
- If there is a WAN link where the cost of the link is based on network traffic. This might also have the added disincentive of being a WAN link that is a dial-on-demand link, which is raised and maintained by the presence of traffic attempting to flow across the interface.
- When you are trying to prevent routing loops. If the routing domain has redundant paths that will be learned by different routing protocol, it is advisable to filter the propagation of one of the paths.


4) In what instances will EIGRP automatically redistribute?

* * EIGRP will automatically redistribute between itself and IGRP as long as both processes are running the same autonomous system number.
EIGRP for IPX automatically redistributes; IPX RIP/SAP and Enhanced IGRP for AppleTalk similarly redistribute automatically into RTMP.


5) Which command is used to view the administrative distance of a route in the routing table?

** The command show ip route displays the administrative distance for each route; two numbers are shown in brackets: the route metric, followed by the administrative distance.


6) When is redistribution required?

** Redistribution is required when there is more than one routing protocol for IP running within the organization and when every part of the network needs connectivity to all the networks.

7) Why does Cisco recommend that you not overlap routing protocols?

** The reason not to overlap routing protocols is that it will increase network traffic, router CPU processing, and memory because of the additional protocol updates. This additional traffic and CPU and memory requirements complicate the routing process. The decision is not simply between multiple paths, but also between the various routing protocols that are advertising them.


8) What is the metric used for in a routing protocol?

** The metric is used to select the best path when multiple paths are available to a remote network.

9) Which has a lower administrative distance, IGRP or OSPF?

** IGRP has an administrative distance of 100, whereas OSPF has an administrative distance of 110. The IGRP path will be entered into the routing table if there are paths offered to the same destination from both protocols.

10) What is the purpose of administrative distance?

** When the routing table is populated with networks that are provided by multiple routing protocols, the administrative distance is used to choose the best path to the remote network.