CCNA v1.1 Exam Review: Routers

Routing is the process of maintaining a table of destination network addresses. A router discards packets for unknown networks.

Types of Routes

Connected

  • When an address and subnet mask is configured on a router’s interface, the router calculates which subnet that interface is on and puts that information in the routing table as a connected route.

Static

  • Manually configured by an administrator; each static route must be configured on each router
  • No overhead in processing, sending, or receiving updates
  • Saves bandwidth and router CPU resources
  • Routing table maintained by administrator

Dynamic

  • A process that automatically exchanges information about available routes
  • Uses metrics to determine the best path to a destination network
  • The routing protocol must be configured on each router
  • Bandwidth is consumed as routing updates are transmitted between routers
  • Router CPU is used to process, send, and receive routing information
  • Routing table maintained by routing process

Default

  • Can be either static or dynamic
  • A router uses the default route if it does not have an explicit route that matches the destination

Administrative Distance

The administrative distance is a number between 0 and 255 that rates the trustworthiness of the source of the routing information. A lower the number is considered better. The administrative distance is used when a router learns about the same route from different routing sources. Some of the default administrative distances are as follows:

Route Source Default Administrative Distance
Connected network 0
Static route 1
Internal EIGRP 90
OSPF 110
RIP (v1 and v2) 120
External EIGRP 170
Unknown 225

Metric

The metric is how a routing protocol measures the “best” path to a destination network. A lower the number is considered better. Some of the routing protocol metrics are as follows:

Routing Protocol Metric
EIGRP Composite metric; defaults to bandwidth and delay so that the fastest, lowest delay path is best.
OSPF Cost; on a Cisco router this is inversely related to bandwidth so that the fastest path is best.
RIP (v1 and v2) Hop count; the path with the least number of hops is best.

Next week we’ll look at routing protocols.

Excerpted and available for download from Global Knowledge White Paper: CCNA v1.1 Exam Review: Critical Concepts of the 640  –  802 CCNA Exam

Resources:
CCNA Cert Check
CCNA Exam Prep Mobile App

Related Courses:
ICND1   —   Interconnecting Cisco Network Devices 1
ICND2   —   Interconnecting Cisco Network Devices 2
CCNAX   —   CCNA Boot Camp v1.1

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