EIGRP interview question and answer part 3

1. Does EIGRP support secondary addresses?

EIGRP and OSPF

Answer: EIGRP does support secondary address. Since EIGRP sources data packets from the primary addresses, Cisco recommends that we configure all routers on a particular subnet with primary addresses that belong to the similar subnet. Routers don’t form EIGRP neighbors over secondary network. For which,  if all of the primary IP addresses of routers don’t agree, problems arises with neighbor adjacency.

2. What does the EIGRP stuck in active message mean?

Answer: When EIGRP returns a stuck in active message, this means that it has not received a reply from a query. It sends a query when a route is lost and another feasible route does not exist inside the topology table. The SIA is caused by 2 sequential events:

• The reported route by the SIA has gone away.
• An EIGRP neighbor (or neighbors) have not replied to the query for that route.

When the SIA occurs, the router clears the neighbor that did not reply for the query. When it happens, determine which neighbor has been cleared. We should Keep in mind that this router can be many hops away.

3. What does the neighbor statement in the EIGRP configuration section do?

Answer: The neighbor command is used in EIGRP in order to define a neighboring router with which to exchange  information of routing. Because of the current behavior of the command, EIGRP exchanges information of routing with the neighbors in the form of unicast packets whenever the neighbor command is configured for interface. EIGRP holds on processing all multicast packets that come inbound on that interface. EIGRP also mutes sending multicast packets on that interface.

The ideal behavior of this command is for EIGRP to start sending EIGRP packets as unicast packets to the specified neighbor, but  don’t stop sending and receiving multicast packets on that interface. As  the command does not behave as intended, the neighbor command must used carefully.

4. Why does the EIGRP passive-interface command remove all neighbors for an interface?

Answer: The passive interface command disables the transmission and receipt of EIGRP hello packets on interface. Not similarly IGRP or RIP, EIGRP sends hello packets in order to form and sustain neighbor adjacency. Not having a neighbor adjacency, EIGRP doesn’t exchange routes with a neighbor. For which the passive interface command prevents the exchange of routes on the interface. Although EIGRP does not  receive or send routing updates on an interface configured with the passive interface command, it includes the address of the interface in routing updates sent out of other non-passive interfaces.

5. What is the difference in metric calculation between EIGRP and IGRP?

Answer: The EIGRP metric is obtained when you multiply the IGRP metric of 256. The IGRP uses only 24 bits in its update packet for the metric field, but 32 bit is used by EIGRP  in its update packet for the metric field. E.g the IGRP metric to a destination network is 8586, but the EIGRP metric will be 8586 x 256 = 2,198,016. Integer division is used when we divide 10^7 by lowest BW, so the calculation involves division of integer, which may leads to a variation from manual calculation.

6. How does EIGRP behave over a GRE tunnel compared to a directly connected network?

Answer: EIGRP will use the same administrative distance and metric calculation to the GRE tunnel. The calculation of cost is based on delay and bandwidth. The bandwidth and delay of the GRE tunnel must be taken from the tunnel interface configured on the router. The tunnel will be treated like a directly connected network.

If there are 2 paths to reach a n/w either through a tunnel interface or VLAN interface, EIGRP prefers the Virtual-Access Interface VLAN interface because the VLAN interface has greater bandwidth than the tunnel interface. To influence the routing through the tunnel interface, It increases the bandwidth parameter of the tunnel interface, or increases the delay parameter of the VLAN interface.

7. Can an OSPF default be originated into the system based on external information on a router that does not itself have a default?

OSPF

Answer: OSPF generates a default only if it is configured using the command default-information originate and if there is a default network in the box from a different process. In OSPF the default route is 0.0.0.0. If we want an OSPF enabled router to generate a default route even if it does not have a default route, use the command default-information originate always.

8. How does Cisco accommodate OSPF routing on partial-mesh Frame Relay networks?

Answer: We can configure OSPF to understand whether it should attempt to use multicast facilities on a multi-access interface. If multicast is available, OSPF usually uses it for its normal multicasts

Cisco IOS Software Release 10.0 includes a feature called sub-interfaces. We can use sub interfaces with Frame Relay to tie together a set of virtual circuits to form a virtual interface, it acts as a single IP subnet. All systems inside the sub-net should be fully meshed.

9. Which address-wild-mask pair should I use for assigning an unnumbered interface to an area?

Answer: When we configured an unnumbered interface, it references  an another interface on the router. When we enable OSPF on the unnumbered interface,  we should use the address-wild-mask pair of interfaces to which the unnumbered interface is pointing.

10. What is the link-state re-transmit interval, and what is the command to set it?

Answer: OSPF sends acknowledgment of every newly received link-state advertisement. It does this by sending LSA packets. After that  LSAs are re-transmitted until they are acknowledged. The link state when re-transmit the interval it defines the time between the re-transmissions. We  can use the command IP OSPF re-transmit interval to set the re-transmit interval. 5 seconds is the default value.

EIGRP Interview Questions part 2

Term What is EIGRP?	Definition Is a Distance Vector Routing Protocol (or Hybrid, because uses Link Advertizement thru Hello packets exchange) that provides loop-free networks and fast convergence.
Term What Protocol uses and AD?	Definition Uses Protocol 88, AD=90 and Summary routes AD=5 External AD=170
Term What is the keepalive packet name and what's its timer	Definition Hello Timers: 5s High Bandwidth and 60s Low Bandwidth ; Dead-Timer= 3 times Hello ip hello-interval eigrp AS secs ip hold-time eigrp AS secs
Term EIGRP Features: Convergence, Bandwidth usage, Subnetting, Load Balancing, Multicasting, Summarization.	Definition Uses very low Bandwidth for reconvergence. By default auto-summary enabled. Uses 224.0.0.10. To sumarize: ip summary-address eigrp [AS] [IP]
Term What is Advertisement Distance, Feasible Distance, Successor, Feasible Successor, Passive Route, Active Route.	Definition -Adv Dist = The metric as reported by a neighbor. From neighbor to its interface for example. -Fea Dist = Historical minimum of the best metric -Successo = The next hop router currently used by this router -Fea succ = A next hop router that can immediately be used if the primary (successor) fails -Fea Cond = A condition that states that an advertised distance must be less than the current feassible distance.
Term What are the EIGRP Databases?	Definition -Neighbor table – stores the adjacencies to other routers -Topology table – entries for each destination -Routing table – sh ip rou
Term EIGRP Packets?	Definition - Hello - Sends keepalive and discovers neighbors. Sent as periodic multicast using 224.0.0.10 - Update- Advertize routes when changes ocurr - Ack - Acknowledgment when an update is received - Query - Used to querry updates from neighbors - Reply - Used to answer a query (unicast)
Term How to turn on classless?	Definition no auto-summary
Term How is the Metric calculated?	Definition 256*(K1*BW+(K2*BW/(256-L)+K3*D)*K5/R+K4 === K1=1 K2=0 K3=1 K4=0 K5=0 === 256*(BW+D) BW= Minimum bandwidth D = Delay L = Load R = Reliability
Term How to summarize?	Definition #int fa0/0 #ip summary-address eigrp (IP) (Subnet) (AD)
Term How to do unequal cost load balancing?	Definition #variance x Multiplies x times the value of FD
Term What is stuck in active SIA?	Definition When the Router hasn't received a Reply to a Query.

EIGRP interview question and answer part-1

. Does EIGRP require an ip default-network command to propagate a default route?

A. Although EIGRP can propagate a default route using the default network method, it is not required. EIGRP redistributes default routes directly.

Q. Should I always use the eigrp log-neighbor-changes command when I configure EIGRP?

A. Yes, this command makes it easy to determine why an EIGRP neighbor was reset. This reduces troubleshooting time.

Q. Does EIGRP support secondary addresses?

A. EIGRP does support secondary addresses. Since EIGRP always sources data packets from the primary address, Cisco recommends that you configure all routers on a particular subnet with primary addresses that belong to the same subnet. Routers do not form EIGRP neighbors over secondary networks. Therefore, if all of the primary IP addresses of routers do not agree, problems can arise with neighbor adjacencies.

Q. What debugging capabilities does EIGRP have?

A. There are protocol-independent and -dependent debug commands. There is also a suite of show commands that display neighbor table status, topology table status, and EIGRP traffic statistics. Some of these commands are:

• show ip eigrp neighbors
• show ip eigrp interfaces
• show ip eigrp topology
• show ip eigrp traffic

Q. What does the word serno mean on the end of an EIGRP topology entry when you issue the show ip eigrp topology command?

A. For example:

show ip eigrp topology
P 172.22.71.208/29, 2 successors, FD is 46163456
via 172.30.1.42 (46163456/45651456), Serial0.2, serno 7539273
via 172.30.2.49 (46163456/45651456), Serial2.6, serno 7539266

Serno stands for serial number. When DRDBs are threaded to be sent, they are assigned a serial number. If you display the topology table at the time an entry is threaded, it shows you the serial number associated with the DRDB.
Threading is the technique used inside the router to queue items up for transmission to neighbors. The updates are not created until it is time for them to go out the interface. Before that, a linked list of pointers to items to send is created (for example, the thread).
These sernos are local to the router and are not passed with the routing update.

Q. What percent of bandwidth and processor resources does EIGRP use?

A. EIGRP version 1 introduced a feature that prevents any single EIGRP process from using more than fifty percent of the configured bandwidth on any link during periods of network convergence. Each AS or protocol (for instance, IP, IPX, or Appletalk) serviced by EIGRP is a separate process. You can use the ip bandwidth-percent eigrp interface configuration command in order to properly configure the bandwidth percentage on each WAN interface. Refer to theEIGRP White Paper for more information on how this feature works.
In addition, the implementation of partial and incremental updates means that EIGRP sends routing information only when a topology change occurs. This feature significantly reduces bandwidth use.
The feasible successor feature of EIGRP reduces the amount of processor resources used by an autonomous system (AS). It requires only the routers affected by a topology change to perform route re-computation. The route re-computation only occurs for routes that were affected, which reduces search time in complex data structures.

Q. Does EIGRP support aggregation and variable length subnet masks?

A. Yes, EIGRP supports aggregation and variable length subnet masks (VLSM). Unlike Open Shortest Path First (OSPF), EIGRP allows summarization and aggregation at any point in the network. EIGRP supports aggregation to any bit. This allows properly designed EIGRP networks to scale exceptionally well without the use of areas. EIGRP also supports automatic summarization of network addresses at major network borders.

Q. Does EIGRP support areas?

A. No, a single EIGRP process is analogous to an area of a link-state protocol. However, within the process, information can be filtered and aggregated at any interface boundary. In order to bound the propagation of routing information, you can use summarization to create a hierarchy.

Q. Can I configure more than one EIGRP autonomous system on the same router?

A. Yes, you can configure more than one EIGRP autonomous system on the same router. This is typically done at a redistribution point where two EIGRP autonomous systems are interconnected. Individual router interfaces should only be included within a single EIGRP autonomous system.
Cisco does not recommend running multiple EIGRP autonomous systems on the same set of interfaces on the router. If multiple EIGRP autonomous systems are used with multiple points of mutual redistribution, it can cause discrepancies in the EIGRP topology table if correct filtering is not performed at the redistribution points. If possible, Cisco recommends you configure only one EIGRP autonomous system in any single autonomous system. You can also use another protocol, such as Border Gateway Protocol (BGP), in order to connect the two EIGRP autonomous systems.

Q. If there are two EIGRP processes that run and two equal paths are learned, one by each EIGRP process, do both routes get installed?

A. No, only one route is installed. The router installs the route that was learned through the EIGRP process with the lower Autonomous System (AS) number. In Cisco IOS Software Releases earlier than 12.2(7)T, the router installed the path with the latest timestamp received from either of the EIGRP processes. The change in behavior is tracked by Cisco bug ID CSCdm47037.

Q. What does the EIGRP stuck in active message mean?

A. When EIGRP returns a stuck in active (SIA) message, it means that it has not received a reply to a query. EIGRP sends a query when a route is lost and another feasible route does not exist in the topology table. The SIA is caused by two sequential events:

• The route reported by the SIA has gone away.
• An EIGRP neighbor (or neighbors) have not replied to the query for that route.

When the SIA occurs, the router clears the neighbor that did not reply to the query. When this happens, determine which neighbor has been cleared. Keep in mind that this router can be many hops away. Refer to What Does the EIGRP DUAL-3-SIA Error Message Mean? for more information.

Q. What does the neighbor statement in the EIGRP configuration section do?

A. The neighbor command is used in EIGRP in order to define a neighboring router with which to exchange routing information. Due to the current behavior of this command, EIGRP exchanges routing information with the neighbors in the form of unicast packets whenever the neighbor command is configured for an interface. EIGRP stops processing all multicast packets that come inbound on that interface. Also, EIGRP stops sending multicast packets on that interface.
The ideal behavior of this command is for EIGRP to start sending EIGRP packets as unicast packets to the specified neighbor, but not stop sending and receiving multicast packets on that interface. Since the command does not behave as intended, the neighbor command should be used carefully, understanding the impact of the command on the network.

Q. Why does the EIGRP passive-interface command remove all neighbors for an interface?

A. The passive-interface command disables the transmission and receipt of EIGRP hello packets on an interface. Unlike IGRP or RIP, EIGRP sends hello packets in order to form and sustain neighbor adjacencies. Without a neighbor adjacency, EIGRP cannot exchange routes with a neighbor. Therefore, the passive-interface command prevents the exchange of routes on the interface. Although EIGRP does not send or receive routing updates on an interface configured with the passive-interface command, it still includes the address of the interface in routing updates sent out of other non-passive interfaces. Refer to How Does the Passive Interface Feature Work in EIGRP?for more information.

Q. Why are routes received from one neighbor on a point-to-multipoint interface that runs EIGRP not propagated to another neighbor on the same point-to-multipoint interface?

A. The split horizon rule prohibits a router from advertising a route through an interface that the router itself uses to reach the destination. In order to disable the split horizon behavior, use the no ip split-horizon eigrp as-numberinterface command. Some important points to remember about EIGRP split horizon are:

• Split horizon behavior is turned on by default.
• When you change the EIGRP split horizon setting on an interface, it resets all adjacencies with EIGRP neighbors reachable over that interface.
• Split horizon should only be disabled on a hub site in a hub-and-spoke network.
• Disabling split horizon on the spokes radically increases EIGRP memory consumption on the hub router, as well as the amount of traffic generated on the spoke routers.
• The EIGRP split horizon behavior is not controlled or influenced by the ip split-horizon command.

For more information on split horizon and poison reverse, refer to Split Horizon and Poison Reverse. For more information on commands, refer to EIGRP Commands.

Q. When I configure EIGRP, how can I configure a network statement with a mask?

A. The optional network-mask argument was first added to the network statement in Cisco IOS Software Release 12.0(4)T. The mask argument can be configured in any format (such as in a network mask or in wild card bits). For example, you can use network 10.10.10.0 255.255.255.252 or network 10.10.10.0 0.0.0.3.

Q. I have two routes: 172.16.1.0/24 and 172.16.1.0/28. How can I deny 172.16.1.0/28 while I allow 172.16.1.0/24 in EIGRP?

A. In order to do this you need to use a prefix-list, as shown here:

router eigrp 100
       network 172.16.0.0
       distribute-list prefix test in
       auto-summary
       no eigrp log-neighbor-changes
       !
       ip prefix-list test seq 5 permit 172.16.1.0/24

This allows only the 172.16.1.0/24 prefix and therefore denies 172.16.1.0/28.
Note: The use of ACL and distribute-list under EIGRP does not work in this case. This is because ACLs do not check the mask, they just check the network portion. Since the network portion is the same, when you allow 172.16.1.0/24, you also allow 172.16.1.0/28.

Q. I have a router that runs Cisco Express Forwarding (CEF) and EIGRP. Who does load-balancing when there are multiple links to a destination?

A. The way in which CEF works is that CEF does the switching of the packet based on the routing table which is populated by the routing protocols such as EIGRP. In short, CEF does the load-balancing once the routing protocol table is calculated. Refer to How Does Load Balancing Work? for more information on load balancing.

Q. How do you verify if the EIGRP Non Stop Forwarding (NSF) feature is enabled?

A. In order to check the EIGRP NSF feature, issue the show ip protocols command. Here is the sample output:

show ip protocols

Routing Protocol is "eigrp 101" Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Default networks flagged in outgoing updates Default networks accepted from incoming updates EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0 EIGRP maximum hopcount 100 EIGRP maximum metric variance 1 Redistributing: eigrp 101 EIGRP NSF-aware route hold timer is 240s Automatic network summarization is in effect Maximum path: 4 Routing for Networks: Routing Information Sources: Gateway Distance Last Update Distance: internal 90 external 170

This output shows that the router is NSF-aware and the route-hold timer is set to 240 seconds, which is the default value.

Q. How can I use only one path when a router has two equal cost paths?

A. Configure the bandwidth value on the interfaces to default, and increase the delay on the backup interface so that the router does not see two equal cost paths.

Q. What is the difference in metric calculation between EIGRP and IGRP?

A. The EIGRP metric is obtained when you multiply the IGRP metric by 256. The IGRP uses only 24 bits in its update packet for the metric field, but EIGRP uses 32 bits in its update packet for the metric field. For example, the IGRP metric to a destination network is 8586, but the EIGRP metric is 8586 x 256 = 2,198,016. Integer division is used when you divide 10^7 by minimum BW, so the calculation involves integer division, which leads to a variation from manual calculation.

Q. What is the EIGRP Stub Routing feature?

A. The Stub routing feature is used to conserve bandwidth by summarizing and filtering routes. Only specified routes are propagated from the remote (Stub) router to the distribution router because of the Stub routing feature. For more information about the Stub routing feature, refer to EIGRP Stub Routing. The EIGRP stub feature can be configured on the switch with the eigrp stub [receive-only] [leak-map name] [connected] [static] [summary] [redistributed]command. This feature can be removed with the no eigrp stub command. When you remove the eigrp stubcommand from the switch, the switch that runs the IP Base image throws this error:

EIGRP is restricted to stub configurations only

This issue can be resolved if you upgrade to Advanced Enterprise Images. This error is documented in CSCeh58135.

Q. How can I send a default route to the Stub router from the hub?

A. Do this under the outbound interface on the hub router with the ip summary-address eigrp X 0.0.0.0 0.0.0.0command. This command suppresses all the more specific routes and only sends the summary route. In the case of the 0.0.0.0 0.0.0.0, it means it suppresses everything, and the only route that is in the outbound update is 0.0.0.0/0. One drawback to this method is that EIGRP installs a 0.0.0.0/0 route to Null0 is the local routing table with an admin distance of 5.

Q. What are different route types in EIGRP?

A. There are three different types of routes in EIGRP:

• Internal Route—Routes that are originated within the Autonomous System (AS).
• Summary Route—Routes that are summarized in the router (for example, internal paths that have been summarized).
• External Route—Routes that are redistributed to EIGRP.

Q. How do you redistribute an IPv6 default route in EIGRP?

A. For redistributing an IPv6 default route in EIGRP, a sample configuration is shown here:

ipv6 prefix-list DEFAULT-ONLY-V6 seq 10 permit ::/0

route-map DEFAULT_2EIGRP-V6 permit 10

match ipv6 address prefix-list DEFAULT-ONLY-V6

router eigrp Starz_EIGRP

address-family ipv6 unicast

redistribute static route-map DEFAULT_2EIGRP-V6

Q. How does EIGRP behave over a GRE tunnel compared to a directly connected network?

A. EIGRP will use the same administrative distance and metric calculation for the GRE tunnel. The cost calculation is based on bandwidth and delay. The bandwidth and delay of the GRE tunnel will be taken from the tunnel interface configured on the router. The tunnel will also be treated like a directly connected network. If there are two paths to reach a network either through a VLAN interface or tunnel interface, EIGRP prefers the Virtual-Access Interface (VAI) VLAN interface because the VLAN interface has greater bandwidth than the tunnel interface. In order to influence the routing through the tunnel interface, increase the bandwidth parameter of the tunnel interface, or increase the delay parameter of the VLAN interface.

Q. What is an offset-list, and how is it useful?

A. The offset-list is an feature used to modify the composite metrics in EIGRP. The value configured in the offset-list command is added to the delay value calculated by the router for the route matched by an access-list. An offset-list is the preferred method to influence a particular path that is advertised and/or chosen.

Q. How can I tag external routes in EIGRP?

A. You can tag routes that EIGRP has learned from another routing protocol using a 32 bit tag value. Starting with ddts CSCdw22585, internal routes can also be tagged. However, the tag value cannot exceed 255 due to packet limitations for internal routes.

Q. What are the primary functions of the PDM?

A. EIGRP supports 3 protocol suites: IP, IPv6, and IPX. Each of them has its own PDM. These are the primary functions of PDM:

• Maintaining the neighbor and topology tables of EIGRP routers that belong to that protocol suite
• Building and translating protocol specific packets for DUAL
• Interfacing DUAL to the protocol specific routing table
• Computing the metric and passing this information to DUAL; DUAL handles only the picking of the feasible successors (FSs)
• Implement filtering and access lists.
• Perform redistribution functions to/from other routing protocols.

Q. What are the various load-balancing options available in EIGRP?

A. The offset-list can be used to modify the metrics of routes that EIGRP learns through a particular interface, or PBR can be used.

Q. What does the %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.254.0.3 (Tunnel0) is down: holding time expired error message mean?

A. This message indicates that the router has not heard any EIGRP packets from the neighbor within the hold-time limit. Because this is a packet-loss issue, check for a Layer 2 problem.

Q. Is there a IPv6 deployment guide that includes EIGRPv6?

A. Refer to Deploying IPv6 in Branch Networks for more information.

Q. From the 16:29:14.262 Poison squashed: 10.X.X.X/24 reverse message, what does poison squashed mean?

A. The router threads a topology table entry as a poison in reply to an update received (the router sets up for poison reverse). While the router is building the packet that contains the poison reverse, the router realizes that it does not need to send it. For example, if the router receives a query for the route from the neighbor, it is currently threaded to poison. Thus, it sends the poison squashed message.

Q. Is it normal that EIGRP takes over 30 seconds to converge?

A. EIGRP taking longer to converge under heavy CPU usage is a normal behavior. EIGRP convergence is faster when you lower the hold time. The lowest values for hello and hold time are 1 second and 3 seconds respectively. For example:

Router(Config)# interface Fa0/0 

!--- (Under an interface directly connected to EIGRP peers.)

Router(Config-if)#ip hello-interval eigrp 1
Router(Config-if)#ip hold-time eigrp 3

Note: Make sure that the hold time is changed on both ends.

VLAN (Virtual Local Area Network)

Definition.

VLAN (Virtual Local Network) is a logically separate IP subnetwork which allow multiple IP networks and subnets to exist on the same-switched network.

VLAN is a logical broadcast domain that can span multiple physical LAN segments. It is a modern way administrators configure switches into virtual local-area networks (VLANs) to improve network performance by separating large Layer 2 broadcast domains into smaller ones. 

 

 By using VLAN a network administrator will be able to group together stations by logical function, or by applications, without regard to physical location of the users.

Each VLAN functions as a separate LAN and  spans one or more switches. This allows host devices to behave as if they were on the same network segment.
For traffic to move between VLANs, a layer 3 device (router) is required.

 

VLAN has three major functions:

 

i.  Limits the size of broadcast domains

ii. Improves network performance

ii.  Provides a level of security

 

How VLAN works.

Lets use this real world scenario: Think about a small organisation with different offices or departments,  all in one building. Some years later, the organisation has expanded and now spans across three buildings. The original network is still the same, but offices and departments computers are spread out across three buildings. The HR offices remain on the same floor and other departments' are on the other floors and buildings.

 

However,  the network administrator wants to ensure that all the office computers share the same security features and bandwidth controls. Creating a large LAN and wiring each department together will constitute a huge task and definitely won’t be easy when it comes to managing the network.

This where VLAN switching comes in, it will be easier to group offices and departments with the resources they use regardless of their location, and certainly easier to manage their specific security and bandwidth needs.

Opting for a switched VLAN allows the network administrator to create groups of logically networked devices that act as if they are on their own independent network, even if they share a common infrastructure with other VLANs. When you configure a VLAN, you can name it to describe the primary role of the users for that VLAN.

Study the figure below for more detail:

 

                                 

 

 

                     

 Books on Cisco Networking, Certification and Exam Resources

 

                                 In summary:

i. VLAN is an independent LAN network.

ii. VLAN allows the student and Faculty Computers to be separated although the share the same       infrastructure.

iii. For easy identification, VLANs can be named.

 

 

1. VLAN = all PCs are assigned with a subnet address defined for VLAN 10
2. Configure the VLAN , assign ports to the VLAN
3. Assign an IP subnet address on the PCs.  

 

Advantages of VLAN:

Security – Security of sensitive data are separated from the rest of the network, decreasing the chances of confidential information breaches.

 Higher performance – Division of Layer 2 networks into multiple logical workgroups (broadcast domains) reduces unnecessary traffic on the network and boosts performance.

Cost reduction - Cost savings result from less need for expensive network upgrades and more on this network.

- See more at: http://orbit-computer-solutions.com/VLAN-and-Trunking.php#sthash.oOY9JEGW.dpuf

IP Routing

To a better understanding of what IP routing is, let’s get acquainted with the basic terms:

IP

Routing

Router

Routing Protocols

 

IP 

 IP (Internet Protocol) is the network protocol used to send user data through the Internet and other smaller networks (LAN or WAN).
IP operates at layer 3 of the OSI model and is often used together with the Transport Control Protocol (TCP) and is referred basically as TCP/IP.

Internet Protocols (IP) uses a unique addressing assigned to computers and other devices interface that helps to determine the source and destination of packets on a network. An example of IP is the Internet Protocol version 4 (IPv4) and the newer Internet Protocol version 6 (IPv6).

 

ROUTING

Routing is the process of taking a packet from one device sending it through the network to another device in a different network.
Communications accross the Internet is one of the best examples of routing.
The internet helps to move data from your computer, across several networks, to reach a destination network. A device that specializes in routing function is called router.
Routers perform routing function if it knows the destination address. Router chooses best routes to remote networks from a list of routes which it stores in its routing table. If routers are not involved in your network, then you are not routing.

Routers uses two ways to know the destination of packets; these are Static and Dynamic routing.

 

ROUTER

 Routers are intermediary network devices. Routers operate at the network layer (OSI Model's layer 3).  The primary function of a router is to move data from one network to another and to help to control broadcast or unnecessary traffic. For a router to be able to do this, it must know the following:
i.    Destination address
ii.   Possible routes to all networks
 iii. Neighboring routers from which it will learn about remote networks
iv. The best route to reach a network
v. How to maintain and verify routing information.

ROUTING PROTOCOLS

Routing protocols are used by routers to dynamically learn remote paths to set of networks and forward data between the networks. These protocols include:
 RIP (Routing Information Protocol  
 EIGRP (Enhanced Internal Gateway Routing Protocol)
 OSPF (Open Shortest Path First)
 BGP (Border Gateway Protocol)

What Is IP Routing?

Networks (LAN or WAN) on the internet are connected to each other via routers. The movement of data from your computer to a known destination (computer) is known as routing.

IP Routing is a summed up process for the set of protocols (IP/TCP) that determine the path that data follows in order to travel across different networks from its source to its destination.

 The moving of data from source to destination across multiple networks is controlled by routers. These series of routers makes use of IP Routing protocols to build up a routing table consisting of remote network addresses.

 

Example below shows how a Network router connects other networks :

 

 

 

R2#show IP route
[Output omitted]
Gateway of last resort is not set
C   192.168.1.32/27 is directly connected, fastEthernet0/1
C   192.168.1.0/27 is directly connected, fastEthernet0/2
C   10.10.1.0/30 is directly connected, serial 0/0/0
The C in the routing table means the networks are directly connected. Remote networks are not found and displayed in the routine table because, we have not added a routing protocol – such as RIP, EIGRP, OSPF etc. etc or configured Static routes.
Looking at the output above, when the network router receive a packet with the destination address of 192.168.1.10, the router will send the packet to interface fastEthernet0/2, and this interface will frame the packet and then send it out on the network segment to Network B.

Switches

Network Switch

 A Network switch is a device that filters, forwards, or floods frames based on the destination address of each frame . 

Switches perform their routing functions at the layers 2 model of the OSI. Some switches  process data at the Network Layer (layer 3), This types of switches are referred to as layer 3 switches or multilayer switches. Switches form an integral parts in networking LAN or WANs . Small office, Home office ( SOHO) applications normally, use a single or an all purpose switches .

The network switch is a very adaptable Layer 2 device; it replaces the hub as the central point of connection for multiple hosts.

 In a more complex role, a switch may be connected to one or more other switches to create, manage, and maintain redundant links and VLAN connectivity. A switch processes all types of traffic in the same way, regardless of how it is used.

Switches moves traffic base on MAC addresses. Each switch maintains a MAC address table in high-speed memory, called content addressable memory (CAM). The switch recreates this table every time it is activated, using both the source MAC addresses of incoming frames and the port number through which the frame entered the switch.

As mentioned earlier, switches operates at the data-link layer of the OSI model, switch function is to create a different collision domain per switch port. Let take an example of Four computers PC 1, PC 2, PC 3, PC 4 attached to switch ports, then PC 1 and PC 2 can transfer data between them so as PC 3 and PC 4, simultaneously without interfering with each other's conversations. 

Unlike the hub, which allows the sharing of bandwidth by all port, run in half-duplex and is prone to collisions of frames and retransmissions. 

With some ISPs and other networking environments where there is a need for much analysis of network performance and security, switches may be connected between WAN routers as places for analytic modules. Some switches  provide in built firewall,  network intrusion detection and performance analysis modules that can plug into switch ports.

                                                                                            

                                                                                            

     

     

Routers

Routers are generally known as intermediate systems, which operates at the network layer of the OSI reference model, routers are devices used to connects two or more networks (IP networks) or a LAN to the Internet.

The router is responsible for the delivery of packets across different networks. The destination of the IP packet might be a web server in another country or an e-mail server on the local area network. It is the responsibility of the router to deliver those packets in a timely manner. The effectiveness of internetwork communications depends on the ability of routers to forward packets in the most efficient way possible.

Routers are now being added to satellites in space. These routers will have the ability to route IP traffic between satellites in space in much the same way that packets are moved on Earth, thereby reducing delays and offering greater networking flexibility.

 

Advantages of a Router

 

In addition to packet forwarding, a router provides other services as well. To meet the demands on today's networks, routers are also used :

 

i. To ensure steady, reliance availability of network connectivity. Routers use alternative parts in the case the primary part fails to the delivery of packets.

 

ii. To provide integrated services of data, video, and voice over wired and wireless networks.

 

For security, router helps in mitigating the impact of worms, viruses, and other attacks on the network by permitting or denying the forwarding of packets.

WAN (Wide Area Network)

When an  individual Company or Organization has locations that are separated by large geographical distances, it will be a matter of necessity to connect these individual locations so as to share, exchange and manager data or communication. To achieve this, the organisation needs a Telecommunication Service Provider (TSP) to interconnect the LANs at the different locations.

 

Telecommunications Service Providers manage large area networks that can span long distances.  TSPs transports voice and data communications on separate networks. These networks that connect LANs in geographically separated locations are referred to as Wide Area Networks (WANs). 

Major characteristics of WANs:

• WANs generally connect devices that are separated by a broader geographical area than cannot be served by a LAN.
• WANs use the services of carriers, such as telephone companies, cable companies, satellite systems, and network providers.
• WANs use serial connections of various types to provide access to bandwidth over large geographic area.

LAN (Local Area Network)

A LAN (Local Area Network) is an individual network that covers a single geographical area, providing networking services and applications to people within a common managerial structure, such as a single business, campus or region.

A LAN is usually administered by a single organization. The administrative control that governs the security and access control policies are enforced on the network level. 

LANs and WANs are very useful to individual organizations. They connect the users within the organization. They allow many forms of communication including exchanging of e-mails, corporate training, and other resource sharing. 

Communication with data, voice, and video is critical to business survival. Consequently, a properly designed LAN is a fundamental requirement for doing business today. You must be able to recognize a well-designed LAN and select the appropriate devices to support the network specifications of a small- or medium-sized business.

Networking Fundamentals

Networking (computers or data) is a type of connection that allows computers to exchange data with each other or various telecommunication devices.

For a network to function, the devices must be interconnected. Network connections can be wired or wireless.

 

All networks are connected to enable communication with different kinds of media (wire or cables), which includes, twisted-pair copper wire cable, coaxial cable, optical fiber, power lines and various wireless technologies.

 

The devices can be separated by a few meters (e.g. via Bluetooth) or nearly unlimited distances (e.g. via the interconnections of the Internet).

In Wired networks, the medium is either copper, which carries electrical signals, or optical fibre, which carries light signals.

 

In Wireless networks, the medium of connection or mode of transmitting is radio waves, space, or microwaves. Wireless networks may include the home wireless connection between a wireless router and a computer with a wireless network card, the global wireless connection between two ground stations, or the communication between devices on earth and satellites then received via the internet.

Examples of Networks are:

 

Local Area Network. (LAN), This is usually a small network constrained to a small geographic area. It is usually within an organization or a college campus.

 

Wide Area Network. (WAN) that is usually a larger network that covers a large geographic area. An example of this is an organization that uses a WAN to interconnect their offices in different countries. The largest and best example of a WAN is the Internet, which is a network of networks, composed of many smaller networks. The Internet is considered the largest network in the world.

 

Wireless LANs and WANs. (WLAN & WWAN) are the wireless equivalent of the LAN and WAN.

But there are no wires between end devices and servers. Communication or data is transferred over sets of radio transceivers or waves. These types of networks are beneficial when it is too costly or inconvenient to run the necessary cables.. The media access protocols for LANs come from the IEEE.

 

 

 

Components of the Network
The path that a message takes from source to destination can be as simple as a single cable connecting one computer to another or as complex as a network that literally spans the globe. This network infrastructure is the platform that supports our human network. It provides the stable and reliable channel over which our communications can occur.

 

Devices and Media

 

Devices and media are the physical elements or hardware of the network. Hardware is often the visible components of the network platform such as a laptop, a PC, game consoles, a Switch, Router or the cabling used to connect the devices. Occasionally, some components may not be so visible. In the case of wireless media, messages are transmitted through the air using invisible radio frequency or infrared waves.

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