Chapter 27 Q and A

thoughtlessskytopNetworking and Communications

Oct 29, 2013 (4 years and 8 months ago)


Chapter 27 Q and A

IS 333


Q1. If
most internet hosts use static routing,
when would a host use dynamic routing

A1. Almost never.


Q2: Does every computer have this routing
software for dynamic routing to
learn about
destinations? What is this software

A2: Every computer

run routing software,
but most don’t. You can install OSPF or RIP or
BGP, configure them, and have them run when
the computer starts up.


Q: How is a static route added to the routing table (aka
forwarding table) on a host?

1. The user has to add it manually.

2. It is added by a routing protocol, such as OSPF, that
runs on the machine.

3. It is added when the user configures an interface with
an IP address.

4. It is added when the host gets an IP address via DHCP.

5. All of the above.

6. Choice 1, 3, or 4

A: 6.


List 3 reasons why routers in an ISP don't use
only static routes.

A: 1. Too many routes to maintain.

2. Routes need to adapt to changing topology.

3. Routes need to adapt for new IPs/customers.


What is an autonomous system, and why is it
important in a discussion about routing

A: An autonomous system is a set of networks
managed by one company/entity. Routers

an AS work together, running an IGP.
Routers at the edge of an AS run an EGP,
summarizing the AS to the world.


Q6: Why
or when is the occasion to use
and EGP
instead of
an IGP
if it's more
complex to
and operate than
and cannot even find the
shortest path

A: EGPs (like BGP) are used between ASs. They
are very good at summarizing routes. And, it is
what is used, so it is what has to be used…


The beginning of section 27.12 talks about RIP.
Do we need to know what RIP is? Does OSPF
replace RIP or is this thrown on top of RIP?

A7. You don

t need to know much about RIP,
except it is the old routing protocol before OSPF
was invented. OSPF replaced RIP.


Can you elaborate more on how OSPF actually
works? The book really
only talks
about its
characteristics, not how it functions

A8: I’ll try…


Since each router connects to many networks, it
seems like the table
would fill
up very quickly

A9. That is not a question.


Q: OSPF is a protocol used for adding
___________________ routes to the

A: dynamic


Q3: T/F: The routing tables on all the machines
in the systems lab are effectively the same.

A: True.


Q: T/F: Route propagation protocols, like RIP,
OSPF, or BGP, run only on routers.

A: True (for the most part).


Q: T/F: Route propagation protocols use the
network to communicate

the network for
which routes need to be configured.

A: True. (which can be a problem)


Q8: T/F: BGP is an example of an IGP.

A: False. BGP is the Border Gateway Protocol,
which is an EGP, good at summarizing routing


Q9: Different applications desire different
characteristics from an "optimal" route through
a network. List two examples of applications
that might desire different characteristics from
the network.

A: Remote desktop application needs low delay.
Web browser app wants high throughput.


10: OSPF uses message authentication for
messages sent between routers. Why? What
could happen if it didn't?

A: Security! Otherwise, some bozo could create
an OSPF packet and send it out and change all
the routes to go through China...