functions:
loss are immediately detectable by a router. FDDI, Token Ring, and carrier detect (CD) failures
can be detected instantaneously. Some types of network changes, however, are more difficult to
detect. If a serial line becomes unreliable but the carrier is not lost, the unreliable link is not
immediately detectable. In addition, some media (Ethernet, for example) do not provide
physical indications such as carrier loss. When a router is reset, other routers might not detect
this immediately. In general, failure detection is dependent on the media involved and the
routing protocol used.
change, the timer settings, and the size of the network. The worst-case scenario for convergence
exists when a routing node fails and the destination is still reachable because the 40-second
default dead timer expires before the SPF is recalculated.
to do this are protocol-dependent. All routing protocols must propagate the changed route.
one route fails, OSPF uses the remaining paths as alternates. OSPF load balancing allows equal
cost by default paths. The cost associated is determined by the interface bandwidth statement
unless otherwise configured to maximize multiple-path routing.
backbone. If a physical connection is impossible, a logical connection can be configured. The
importance of Area 0 makes it essential that the CCDP consider first and foremost which routers
and devices should be included in Area 0. Do not place client workstations in Area 0. Keep all
local workgroup traffic off the backbone. Use the backbone strictly as a transit area.
successful design include the following: