background image
Chapter 1
Scaling Large Internetworks
Some Cisco IOS features that serve to provide stability and availability are
as follows:
Reachability OSPF and EIGRP use expanded metrics that can go
beyond the hop-count limitations of distance-vector routing algorithms.
These routing protocols analyze a combination of factors to establish the
real cost of a path to a network, making Cisco routers able to support very
large internetworks.
Convergence Scalable routing protocols can converge quickly because
of each router's complete understanding of the internetwork and ability
to detect problems.
Since it's the network administrator's responsibility to make sure users don't
experience delays in responsiveness as the internetwork grows, they must be
keenly aware of the latency factor that each piece of equipment (routers,
switches, and bridges) contributes to the internetwork. The Cisco IOS pro-
vides mitigation for the latency needs of each protocol running on your inter-
network, with features such as
Alternate paths routing Because OSPF and EIGRP build a complete
map of the internetwork, a router can easily reroute traffic to an alternate
path if a problem occurs.
Load balancing Through the EIGRP and OSPF routing algorithms, the
Cisco IOS is able to perform load balancing. This allows for redundant
links and for more bandwidth to be available to locations needing more
than just one link. For example, if two T1 WAN links were installed
between buildings, the actual bandwidth between them would reach
approximately 3Mbps.
Tunneling Running a tunneling protocol affords the ability to commu-
nicate across WAN links that were previously unreachable. For example,
if you have a WAN link that supports only TCP/IP and you want to man-
age a Novell NetWare server that supports only IPX, you could tunnel
IPX packets inside of IP packets to achieve your goal.
Dial backup You can configure dial-backup links for redundancy on
your WAN links and to add extra bandwidth whenever it becomes satu-
rated, enhancing the link's reliability and availability.
Copyright ©2001 SYBEX , Inc., Alameda, CA