| A | B |
|---|
| Setup mode | With the setup mode command facility, you can answer questions in the system configuration dialog. This facility prompts you for basic configuration information. The answers you enter allow the router to use a sufficient, but minimal-feature, router configuration |
| The initial IP routing table | The Cisco IOS software learns about this IP address and mask information from a configuration that has been input from some source. The initial source of addressing is a user who types it into a configuration file |
| How a router learns about destinations | static routes; default routes; dynamic routing |
| static routes | manually defined by the system administrator as the next hop to a destination; useful for security and traffic reduction |
| default routes | manually defined by the system administrator as the path to take when there is no known route to the destination |
| dynamic routing | the router learns of paths to destinations by receiving periodic updates from other routers. |
| administrative distance | a rating of the trustworthiness of a routing information source, expressed as a numeric value from 0 to 255. The higher the number, the lower the trustworthiness rating. |
| ip default-network | establishes a default route in networks using dynamic routing protocols |
| autonomous system | An autonomous system consists of routers, run by one or more operators, that present a consistent view of routing to the external world. The Network Information Center (NIC) assigns a unique autonomous system to enterprises. This autonomous system is a 16 bit number. A routing protocol such as Cisco's IGRP requires that you specify this unique, assigned autonomous system number in your configuration. |
| Interior versus exterior routing protocols | Exterior routing protocols are used for communications between autonomous systems. Interior routing protocols are used within a single autonomous system. |
| Examples of IP routing protocols | RIP; IGRP; EIGRP; OSPF |
| RIP | a distance-vector routing protocol |
| IGRP | Cisco's distance-vector routing protocol |
| OSPF | a link-state routing protocol |
| EIGRP | a balanced hybrid routing protocol |
| router command | The router command starts a routing process |
| network command | The network command is required because it enables the routing process to determine which interfaces will participate in the sending and receiving of routing updates. The network numbers must be based on the network class addresses, not subnet addresses or individual host addresses. Major network addresses are limited to Class A, B and C network numbers |
| Key elements of RIP | · 1) It is a distance-vector routing protocol; 2) Hop count is used as the metric for path selection; 3) If the hop count is greater than 15, the packet will be discarded; 4) By default, routing updates are broadcast every 30 seconds. |
| show ip protocol | displays values, about routing timers and network information, that are associated with the entire router. Use this information to identify a router that you suspect of delivering bad routing information. |
| Key characteristics of IGRP | 1) versatility that enables it to automatically handle indefinite, complex topologies; 2) flexibility for segments that have different bandwidth and delay characteristics; 3) scalability for functioning in very large networks. The IGRP routing protocol by default uses two metrics, bandwidth and delay. IGRP can be configured to use a combination of variables to determine a composite metric. Those variables include 1) bandwidth; 2) delay; 3) load; 4) reliability |
| show ip interfaces | displays the status and global parameters associated with all IP interfaces. The Cisco IOS software automatically enters a directly-connected route in the routing table if the interface is one through which software can send and receive packets. |
| show ip route | displays the contents of an IP routing table. The table contains a list of all known networks and subnets and the metrics associated with each entry. |
| debug ip rip | displays RIP routing updates as they are sent and received. |
| Typical layer 1 errors | · 1) broken cables; 2) disconnected cables; 3) cables connected to the wrong ports; 4) intermittent cable connection; 5) wrong cables used for the task at hand (must use rollovers, cross-connects, and straight-through cables correctly); 6) transceiver problems; 7) DCE cable problems; 8) DTE cable problems; 9) devices turned off |
| Typical layer 2 errors | · 1) improperly configured serial interfaces; 2) improperly configured Ethernet interfaces; 3) improper encapsulation set (HDLC is default for serial interfaces); 4) improper clockrate settings on serial interfaces |
| Typical layer 3 errors | · 1) routing protocol not enabled; 2) wrong routing protocol enabled; 3) incorrect IP addresses; 3) incorrect Subnet Masks; 4) incorrect DNS to IP bindings |
