Basic Networking Assessment interview and answers
What layer of the OSI reference model to bridges
and switches operate.
Bridges and switches are data communications
devices that operate principally at Layer 2 of the OSI reference model. As
such, they are widely referred to as data link-layer devices.
What is controlled at the link layer?
Bridging and switching occur at the link layer,
which controls data flow, handles transmission errors, provides physical (as
opposed to logical) addressing, and manages access to the physical medium.
Under one popular classification scheme what are
bridges classified as?
Local or Remote: Local bridges provide a direct
connection between multiple LAN segments in the same area. Remote bridges
connect multiple LAN segments in different areas, usually over
telecommunications lines.
What is a switch?
Switches are data link-layer devices that, like
bridges, enable multiple physical LAN segments to be interconnected into a
single larger network.
Name the different areas of network management.
Configuration, accounting, fault, security, and
performance.
What are the goals of performance management?
Measure and make available various aspects of
network performance so that internetwork performance can be maintained at an
acceptable level.
What are the goals of configuration management?
Monitor network and system configuration
information so that the effects on network operation of various versions of
hardware and software elements can be tracked and managed.
What are the goals of accounting management?
Measure network utilization parameters so that
individual or group uses on the network can be regulated appropriately.
What are the goals of fault management?
Detect, log, notify users of, and automatically
fix network problems to keep the network running effectively.
What are the goals of security management?
Control access to network resources according to
local guidelines so that the network cannot be sabotaged and so that sensitive
information cannot be accessed by those without appropriate authorization.
Shouldn't all 10Base-T networks just be upgraded
to 100 Mbps? Why or why not?
Not necessarily-if the current 10Base-T network
is repeater-based, replacing the repeaters with 10/100 nonsaturating switches
would result in an automatic n times increase in the average available
bandwidth for each end station.
Which 100Base version(s) are recommended? Why?
100Base-TX is recommended if the horizontal
wiring is Category5 or better UTP. If the horizontal cabling is Category 3,
100BaseT4 can be used, but it may be difficult to acquire (some reports
indicate that because 100Base-TX was available more than a year before T4, it
captured as much as 95 percent of the market). 100Base-T2 is not available.
Which 1000Base version(s) are recommended? Where
would they be used?
1000Base-T, is recommended if the horizontal
cabling is Category 5 or better UTP. 1000Base-SX can be used if the horizontal
cabling is multimode optical fiber, as well as for some multimode backbones.
1000Base-LX can be used for either single-mode or multimode optical fiber (see
Table 7-5). 1000Base-CX can be used for short-haul equipment-room jumpers up to
25 meters.
What cable types should be used for new
networks? For upgrading existing networks? Why?
New or replacement UTP links may be Category 5E
or better to allow for data rate growth to 1000 Mbps. Multimode fiber may be
used as indicated in Table 7-5 for 1000Base-SX, or as noted in the paragraph
following Table 7-5 for 1000Base-LX. (These fibers will also provide future support
for shorter distances [between 100 and 300 meters, depending on the wavelength]
at 10,000 Mbps.) To be truly future-proof and to ensure that you will be able
to operate longer-distance backbones, choose single-mode fiber.
How do you know when a network needs to be
upgraded? Where do you start?
There are several ways:
§ Your users will tell you (but often only after
they have crossed the frustration threshold).
§ Your network management system should be capable
of indicating the load characteristics for each DCE port.
§ Your organization is considering adding new
applications (such as multimedia) that will require more communication
bandwidth.
§ Your organization is growing, and there are not
sufficient DCE ports in the right locations to accommodate the additional
users.
After you have determined the need, you can consider the options.
Remember that the network elements with the longest useful life (the link
media, followed by the network servers and network switches) can also be the
most expensive to replace. Choose with an eye to future growth, and consider
reusing these elements wherever possible.
Token Ring networks differ from Ethernet
networks in what ways?
They are deterministic, meaning that the time
before the next token will be passed can be calculated. Extra credit: There are
fewer collisions on a Token Ring network than on Ethernet.
For what types of applications is this
beneficial?
Applications in which delay must be predictable,
and applications that require a robust network operation.
Name at least three benefits of implementing
HSSI technology in a network.
Benefits include these: HSSI provides high-speed
data communication over WAN and LAN links.
HSSI uses differential emitter-coupled logic (ECL), which provides
high-speed data transfer with low noise levels.
HSSI uses a subminiature FCC-approved 50-pin connector that is
smaller than its V.35 competitor.
The HSSI cable uses the same number of pins and wires as the Small
Computer Systems Interface 2 (SCSI-2) cable, but the HSSI electrical
specification is more concise.
HSSI makes bandwidth resources easy to allocate, making T3 and
other broadband services available and affordable.
HSSI requires the presence of only two control signals ("DTE
available" and "DCE available"), making it highly reliable
because there are fewer circuits that can fail.
HSSI performs four loopback tests for reliability.
Name the four loopback tests that HSSI performs.
Cable test, DCE test, Telco line test, DTE test.
In downstream-on-demand distribution, how does
the upstream LSR know that it needs a label?
The unicast routing protocols distribute the
presence of a network. When the upstream LSR needs to forward a frame to the
new network, it can request a label from the downstream LSR.
FIB refers to a forwarding information base. How
does this differ from an LFIB?
FIB tables are developed from routing protocols
such as OSPF, BGP, IS-IS, and so on. LSRs reference these tables whenever they
need a label/route binding. The actual bindings are contained in the LFIB that
displays destination networks/labels/interfaces in one table.
What are the two LDP modes?
One mode is downstream unsolicited distribution,
in which an LSR announces a binding without any request from a neighbor LSR.
The other mode is downstream-on-demand, in which an LSR requests a binding.
It is highly recommended that neighbor LSRs
operate in the same LDP mode. What might result if an upstream LSR operates in
downstream unsolicited distribution mode and the downstream LSR runs in
downstream-on-demand mode?
This is a case in which labels would never get
distributed. The upstream LSR assumes that it never needs to ask for a binding,
while the downstream unit assumes that it should never create one unless
explicitly requested. Neither LSR will trigger a label distribution.
If a vendor's router already uses high-speed
switching and caching techniques for forwarding frames, then performance may
not be a valid motivation for using MPLS. Is there any other reason that might
merit deployment of MPLS in such a network?
Traffic engineering could further enhance the
network by enabling an administrator to select a path between locations based
on policy. The policy may take into consideration parameters such as network
loading, security, and several other elements. Otherwise, the administrator
leaves the path selection to the destination-based routing protocols.
Name the four key technologies that are used by
EIGRP.
EIGRP employs four key technologies, including
neighbor discover/recovery, Reliable Transport Protocol (RTP), Diffusing Update
ALgorithm (DUAL) finite-state machine, and a modular architecture that enables
support for new protocols to be easily added to an existing network.
Explain why EIGRP is more efficient in operation
than IGRP.
Unlike most other distance vector routing
protocols, EIGRP does not mandate a periodic update of routing tables between
neighboring routers. Instead, it employs a neighbor discovery/recovery
mechanism to ensure that neighbors remain aware of each other's accessibility.
As long as a router receives periodic hello packets from its neighbors, it can
assume that those neighbors remain functional. More importantly, it can assume
that all of its routes that rely upon passage through those neighbors remain
usable. Thus, EIGRP is much more efficient than conventional distance vector
routing protocols because it imposes much less overhead on routers and
transmission facilities during normal operation.
How does RTP enable improved convergence times?
RTP is responsible for providing guaranteed
delivery of EIGRP packets between neighboring routers. However, not all of the
EIGRP packets that neighbors exchange must be sent reliably. Some packets, such
as hello packets, can be sent unreliably. More importantly, they can be
multicast rather than having separate datagrams with essentially the same
payload being discretely addressed and sent to individual routers. This helps
an EIGRP network converge quickly, even when its links are of varying speeds.
Why does EIGRP tag certain routes?
EIGRP supports both internal and external
routes. Routes that are internal to an AS are completely contained within that
AS. External routes are those that are learned from neighbors that lie outside
the AS. External routes are tagged with information that identifies their
origin. This enables a network administrator to develop customized interdomain
routing policies.
Can IBGP be used in place of an IGP (RIP, IGRP,
EIGRP, OSPF, or ISIS)?
Yes and no. Remember that the next-hop
information from EBGP is carried into IBGP. If IBGP does not have a route to
reach the next hop, then the route will be discarded. Typically an IGP needs to
be used to exchange routes to the next hop, but this can be achieved by using
static routes on all the routers running IBGP. So, the answer is yes if you
want to use and maintain static routes. Otherwise, the answer is no.
Assume that a BGP router is learning the same
route from two different EBGP peers. The AS_path information from peer 1 is
{2345,86,51}, and the AS_path information from peer 2 is {2346,51}. What BGP
attributes could be adjusted to force the router to prefer the route advertised
by peer 1?
Weight and local preference. Both have a higher
preference than AS_path length.
Can BGP be used only by Internet service
providers?
No. BGP can be used to scale large enterprise
networks. A large network can be divided into segments, with each segment
running an IGP. Routing information between segments could then be exchanged
using BGP.
If a directly connected interface is
redistributed into BGP, what value will the origin attribute have for this
route?
Any redistributed route will have an origin of
incomplete.
When using OSPF, can you have two areas attached
to each other where only one AS has an interface in Area 0?
Yes, you can. This describes the use of a
virtual path. One area has an interface in Area 0 (legal), and the other AS is
brought up and attached off an ABR in Area 1, so we'll call it Area 2. Area 2
has no interface in Area 0, so it must have a virtual path to Area 0 through
Area 1. When this is in place, Area 2 looks like it is directly connected to
Area 0. When Area 1 wants to send packets to Area 2, it must send them to Area
0, which in turn redirects them back through Area 1 using the virtual path to
Area 2.
Area 0 contains five routers (A, B, C, D, and
E), and Area 1 contains three routers (R, S, and T). What routers does Router T
know exists? Router S is the ABR.
Router T knows about routers R and S only.
Likewise, Router S only knows about R and T, as well as routers to the ABR in
Area 0. The AS's separate the areas so that router updates contain only
information needed for that AS.
What is a VPN?
A VPN is a generic term that describes any combination
of technologies that can be used to secure a connection through an otherwise
unsecured or untrusted network.
Explain the difference between L2TP's LAC and
LSN.
The LAC provides authentication and access
concentration for remote users. After a remote user is authenticated, that
user's communications session is then forwarded to the LSN, which provides
access to that user's home network.
What additional functionality does IPSec offer
an L2TP implementation?
L2TP's native security mechanisms build on the
assumption that the nature of a point-to-point connection satisfies most of a
remote user's security requirements. IPSec complements L2TP by offering a more
robust set of technologies for authenticating remote users and for securing
data in transit through foreign networks by encrypting data.
What is a tunnel?
A tunnel is a logical structure that
encapsulates the frame and data of one protocol inside the Payload or Data
field of another protocol. Thus, the encapsulated data frame may transit
through networks that it would otherwise not be capable of traversing.
What are MIBs, and how are they accessed?
A Management Information Base (MIB) is a
collection of information that is organized hierarchically. MIBs are accessed
using a network-management protocol such as SNMP. They are comprised of managed
objects and are identified by object identifiers.
SNMP uses a series of _____ and ______to manage
the network.
Gets and Puts. SNMP uses a Get object and a Put
object to manage devices on a network such as get counters.
Name three of the seven fields of the SNMP v2
GETBULK.
PDU Type, Request ID, Nonrepeaters, Max
Repetitions, Variable Bindings (the variable bindings consists of variable
object fields that make up the three remaining fields).
On what concept is network caching based?
Based on the assumption that users access the
same content over and over.
What are two secondary benefits of implementing
caching technology?
1. Secure access and control.
2. Operational logging-administrators can log how many hits sites
receive.
Provide a brief description of
network-integrated caching technology.
Network-integrated caching technology combines
system-level software and hardware. Network-integrated caches must be managed
like network equipment, designed like high-density hardware, and transparently
inserted into the network.
How do Cisco cache engines ensure that web pages
are kept up to date?
By obeying HTTP caching standards that dictate
which elements on a page can be cached and which cannot. Those that are not are
retrieved from the source every time they are accessed.
Name an object that can be saved in cache
memory, and one that cannot.
Saved in cache: rotating banners, GIFs and
JPEGs, toolbars, navigation bars. Noncacheable: CGI-generated responses.
