4 Routing and Internetworking Free Online FlashCards

What does a router do with an IP packet?

A router examines a packet’s destination IP address, selects a path, and forwards the packet through an appropriate interface.

How do destination IP and link-layer addresses differ in forwarding?

The destination IP address guides routing across networks. The link-layer address is used to deliver a frame on the current local link.

What information does a routing table route commonly contain?

A route commonly specifies a destination network prefix, next hop or direct connection, outgoing interface, and metric or other route-comparison information.

How do the RIB and FIB differ?

The RIB is used for route selection; selected forwarding entries are installed in the FIB for packet lookups.

Which route wins by longest-prefix match for 10.2.4.7: 10.0.0.0/8 or 10.2.0.0/16?

IP forwarding generally selects the matching route with the most specific prefix. For destination 10.2.4.7, 10.2.0.0/16 takes precedence over 10.0.0.0/8.

When can an IPv4 default route be used?

For IPv4, 0.0.0.0/0 is the least-specific route and can be used when no more-specific route matches.

What does a routing metric indicate, and what does it not guarantee?

A metric measures route cost, but its meaning depends on the protocol. A lower metric does not necessarily mean a path is faster in real-world conditions.

How does a routing protocol differ from a static route?

Routing protocols exchange reachability information and can adapt routes when links or routers change. A static route is configured manually and does not automatically learn a replacement path.

Where do IGPs operate, and what role does BGP serve?

IGPs exchange routes within an autonomous system; examples include RIP and OSPF. BGP is the principal inter-domain routing protocol, exchanging routes between autonomous systems.

How does distance-vector routing work, and what are RIP’s hop limits?

Distance-vector routers share route distances and next-hop information with neighbors. RIP uses a hop-based metric: 15 is the largest usable value, and 16 means unreachable.

How does OSPF use link-state information?

Link-state routers distribute information about their local links, build a topology database, and calculate shortest paths. OSPF uses link costs and can support equal-cost paths.

How does BGP select routes using path-vector information?

Path-vector routers advertise reachable prefixes with path information and attributes. BGP uses these attributes and routing policy, rather than simply selecting the fewest physical links.