3 IP Connectivity and Routing Free Online FlashCards

How does a router choose among routes that match a destination?

The longest prefix match: the most specific matching route is selected before route-source preferences such as administrative distance are compared.

What does administrative distance compare?

Administrative distance compares competing sources for the same prefix; the lower value is preferred. It is distinct from a routing protocol’s metric.

Which metric does OSPF use, and which value is preferred?

OSPF compares routes using cost, and a lower total cost is preferred.

What is the purpose of a default route?

A default route is the gateway of last resort: it matches destinations for which no more-specific route exists.

What makes a static route a floating static route?

It is a backup static route configured with a higher administrative distance than the preferred route. It can be installed if the preferred route disappears and its next hop is reachable.

What is a limitation of a static route when topology changes?

A static route does not automatically adapt to topology changes unless suitable tracking or backup behavior is configured.

How does OSPF calculate routes?

OSPF is a link-state interior gateway protocol. Routers exchange link-state information, build an area database, and calculate shortest paths using the SPF algorithm.

How does Cisco IOS select an OSPF router ID if none is configured?

A manually configured ID takes precedence. Otherwise, Cisco IOS prefers the highest loopback address; if there is no loopback, it uses the highest active interface address.

Must neighboring Cisco routers use the same OSPF process ID?

The OSPF process ID is locally significant; neighboring Cisco routers do not need to use the same process ID.

What settings can prevent OSPF neighbors from forming an adjacency?

Common causes include mismatched areas, Hello or dead intervals, authentication, subnet configuration, or network types.

How is the OSPF DR chosen on a broadcast network?

On broadcast networks, the highest interface priority wins; a priority of zero makes a router ineligible. If priorities tie, the highest router ID wins.

How does an OSPF wildcard mask relate to a subnet mask?

A wildcard mask is the inverse of the subnet mask. For example, 0.0.0.255 corresponds to 255.255.255.0.