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Etherchannels are in use all over the world, as well as on your CCNA and CCNP exams. Learn how to build and support an EC in this tutorial from Chris Bryant, CCIE #12933.

Cisco CCNA / CCNP Certification: How And Why To Build An Etherchannel

Cisco CCNA / CCNP Certification: How And Why To Build An EtherchannelCCNA and CCNP candidates are well-versed in Spanning-Tree Protocol, and one of the great things about STP is that it works well with little or no additional configuration. There is one situation where STP works against us just a bit while it prevents switching loops, and that is the situation where two switches have multiple physical connections.You would think that if you have two separate physical connections between two switches, twice as much data could be sent from one switch to the other than if there was only one connection. STP doesn't allow this by default, however in an effort to prevent switching loops from forming, one of the paths will be blocked. SW1 and SW2 are connected via two separate physical connections, on ports fast0/11 and fast 0/12. As we can see here on SW1, only port 0/11 is actually forwarding traffic. STP has put the other port into blocking mode (BLK).SW1#show spanning vlan 10(some output removed for clarity)Interface Role Sts Cost Prio.Nbr TypeFa0/11 Root FWD 19 128.11 P2pFa0/12 Altn BLK 19 128.12 P2pWhile STP is helping us by preventing switching loops, STP is also hurting us by preventing us from using a perfectly valid path between SW1 and SW2. We could literally double the bandwidth available between the two switches if we could use that path that is currently being blocked.The secret to using the currently blocked path is configuring an Etherchannel. An Etherchannel is simply a logical bundling of 2 - 8 physical connections between two Cisco switches.Configuring an Etherchannel is actually quite simple. Use the command "channel-group 1 mode on" on every port you want to be placed into the Etherchannel. Of course, this must be done on both switches if you configure an Etherchannel on one switch and don't do so on the correct ports on the other switch, the line protocol will go down and stay there.The beauty of an Etherchannel is that STP sees the Etherchannel as one connection. If any of the physical connections inside the Etherchannel go down, STP does not see this, and STP will not recalculate. While traffic flow between the two switches will obviously be slowed, the delay in transmission caused by an STP recalculation is avoided. An Etherchannel also allows us to use multiple physical connections at one time.Here's how to put these ports into an Etherchannel:SW1#conf tEnter configuration commands, one per line. End with CNTL/Z.SW1(config)#interface fast 0/11SW1(config-if)#channel-group 1 mode onCreating a port-channel interface Port-channel 1SW1(config-if)#interface fast 0/12SW1(config-if)#channel-group 1 mode onSW2#conf tEnter configuration commands, one per line. End with CNTL/Z.SW2(config)#int fast 0/11SW2(config-if)#channel-group 1 mode onSW2(config-if)#int fast 0/12SW2(config-if)#channel-group 1 mode onThe command "show interface trunk" and "show spanning-tree vlan 10" will be used to verify the Etherchannel configuration. SW2#show interface trunk (some output removed for clarity)Port Mode Encapsulation Status Native vlanPo1 desirable 802.1q trunking 1SW2#show spanning vlan 10 (some output removed for clarity)Interface Role Sts Cost Prio.Nbr TypePo1 Desg FWD 12 128.65 P2pBefore configuring the Etherchannel, we saw individual ports here. Now we see "Po1", which stands for the interface "port-channel1". This is the logical interface created when an Etherchannel is built. We are now using both physical paths between the two switches at one time!That's one major benefit in action let's see another. Ordinarily, if the single open path between two trunking switches goes down, there is a significant delay while another valid path is opened - close to a minute in some situations. We will now shut down port 0/11 on SW2 and see the effect on the etherchannel.SW2#conf tEnter configuration commands, one per line. End with CNTL/Z.SW2(config)#int fast 0/11SW2(config-if)#shutdown3w0d: %LINK-5-CHANGED: Interface FastEthernet0/11, changed state to administratively downSW2#show spanning vlan 10VLAN0010Spanning tree enabled protocol ieeeInterface Role Sts Cost Prio.Nbr TypePo1 Desg FWD 19 128.65 P2pSW2#show interface trunkPort Mode Encapsulation Status Native vlanPo1 desirable 802.1q trunking 1The Etherchannel did not go down! STP sees the Etherchannel as a single link therefore, as far as STP is concerned, nothing happened.Building an Etherchannel and knowing how it can benefit your network is an essential skill for CCNA and CCNP success, and it comes in very handy on the job as well. Make sure you are comfortable with building one before taking Cisco's exams!

Enhance your computer knowledge with latest technology at ABCO

Enhance your computer knowledge with latest technology at ABCO

There are several types of computer training course available to the person seeking to learn about computers today. Generally the term "computer training" comprises everything related to the computer as a whole. This training consists of lessons on the various parts of the computer, their functions and necessities and then the manner to compute or run the computer. Also the content of this kind of computer trainings are based on the term or duration of the training procedure. To start, it would be a good course of action to look at classes teaching the basics of how to operate a computer. It is a good idea in the computer training course to also learn some basics about the internal operation of the computer (i.e., what makes it tick, how it works). Student self-respect is also important. A good trainer must develop the feeling that it's okay to be wrong and that being wrong does not imply that a student is ignorant. The importance of computer is nowadays felt in each and every sphere. Right from the beginners of the primary schools to the big industrialists, everyone comes in touch with the computers. This immense importance of the computers has led to the necessity of computer training to a great extent. Therefore it will be worthwhile to know about the several types of computer training and its impact and usefulness in our life.Moving on from the basics, a computer training course should teach more advanced concepts as well. Some of these concepts would include back-up procedures, file maintenance, and data recovery. In the short term computer training classes, the emphasis is put on making the student aware of the general and basic computer term and a basic learning is provided with which the primary computer functions can be done. We prepare students by delivering hands-on job oriented training which teaches them how to apply the knowledge that they gain in classes along with preparing them to pass the vendor based certification exams. We have partnered with Microsoft, Oracle, Linux , Cisco Systems, Prometric testing center and as such offer wide variety of computer training that include but are not limited to Microsoft Certification, A+ training, CISCO Certification Course, Oracle Certification Course, Internet and Microsoft Office 2003. The importance of the Computer training course is rapidly increasing as it is required in each and every field in this fast growing world. Even the housewives too need to know the basics of the computer if they want to be an efficient home manager. Shopping, cooking, cleaning everything has become computerized nowadays. Even for guiding the little one in their school homework, the mother should have the primary computer knowledge. Keeping in mind this vital role of the computers numerous "Computer training course" institutions have opened up where any class and any age group can get admitted and take lessons. Also, the online Computer training course courses have made this procedure far more easy and accessible for the learners. Those who are very busy and find it tough to manage time for rushing to the institutes have been helped to a great extent by this online computer learning system. ABCO Technology specializes in providing Computer Training and Consulting for the Information Technology Industry. Computer Training is provided by experienced, certified industry experts that have years of seasoning in their respective field of Information Technology.If you would like to do Computer training course courses at ABCO Technology, then kindly free to visit our website:- http://www.abcotechnology.com/

Cisco CCNA Certification: Broadcasts, Unicasts, And Multicasts

Cisco CCNA Certification:  Broadcasts, Unicasts, And Multicasts

When you begin your CCNA studies, you get hit with a lot of different networking terms right away that you might not be familiar with. What makes it a little more confusing is that a lot of these terms sound a lot alike. Here, we're going to discuss the differences between broadcasts, multicasts, and unicasts at both the Data Link (Layer 2) and Network (Layer 3) layers of the OSI model.A broadcast is simply a unit of information that every other device on the segment will receive. A broadcast is indicated by having every bit of the address set to its highest possible value. Since a hexadecimal bit's highest value is "f", a hexadecimal broadcast is ff-ff-ff-ff-ff-ff (or FF-FF-FF-FF-FF-FF, as the upper case does not affect hex value). The CCNA exam will demand you be very familiar with hex conversions, so if you're not comfortable with these conversions, get comfortable with them before taking the exam!At layer 3, a broadcast is indicated by setting every bit in the 32-bit binary string to "1", making the dotted decimal value 255.255.255.255. Every host on a segment will receive such a broadcast. (Keep in mind that switches will forward a broadcast, but routers do not.) In contrast to a broadcast, a unicast is a packet or frame with only one destination. There is a middle ground between broadcasts and unicasts, and that is a multicast. Where a broadcast will be received by all, and a unicast is received by only one host, a multicast will be received by multiple hosts, all belonging to a "multicast group". As you climb the Cisco certification pyramid, you'll be introduced to creating multicast groups and controlling multicast traffic, but for your CCNA studies you need only keep certain multicast groups in mind.Class D addresses are reserved for multicasting this range is 224.0.0.0 - 239.255.255.255. The addresses 224.0.0.0 - 224.255.255.255 are reserved for use by network protocols on a local network segment, and like broadcasts, routers will not forward these multicast packets. (Packets with these addresses are sent with a Time To Live of 1.)As a CCNA candidate, you should know that OSPF routers use the address 224.0.0.5 to send hellos, EIGRP routers use 224.0.0.10 to send updates, and RIP version 2 uses 224.0.0.9 to send routing updates. RIP version 1 and IGRP both broadcast their updates.Multicasting gets a bit more complicated as you go from your CCNA to the CCNP and CCIE, but by simply understanding what multicasting is, you go a long way toward securing the CCNA.

Cisco CCNP / BSCI Certification: Route Redistribution And The Seed Metric

Cisco CCNP / BSCI Certification: Route Redistribution And The Seed Metric

In the first part of this free CCNP / BSCI tutorial, we looked at how leaving one simple word out of our route redistribution configuration - "subnets" - resulted in an incomplete routing table when redistributing routes from RIP to OSPF. (If you missed that part of the tutorial, visit my website's "Free Tutorials" section.) Today, we'll look at redistributing OSPF routes into RIP and identify another common redistribution error.We are using a three-router network. R5 is running RIP, R1 is serving as a hub between R5 and R3 and is running RIP and OSPF, and R3 is running OSPF. To begin this lab, we'll add three loopbacks to R3 and advertise them to R1 via OSPF.R3(config)#int loopback33R3(config-if)#ip address 33.3.3.3 255.255.255.255R3(config-if)#int loopback34R3(config-if)#ip address 34.3.3.3 255.255.255.255R3(config-if)#int loopback35R3(config-if)#ip address 35.3.3.3 255.255.255.255R3(config-if)#router ospf 1R3(config-router)#network 33.3.3.3 0.0.0.0 area 1R3(config-router)#network 34.3.3.3 0.0.0.0 area 1R3(config-router)#network 35.3.3.3 0.0.0.0 area 1R1 sees all three of these routes in its routing table.R1#show ip route ospf 34.0.0.0/32 is subnetted, 1 subnetsO IA 34.3.3.3 [110/65] via 172.12.123.3, 00:00:55, Serial0 35.0.0.0/32 is subnetted, 1 subnetsO IA 35.3.3.3 [110/65] via 172.12.123.3, 00:00:45, Serial0 33.0.0.0/32 is subnetted, 1 subnetsO IA 33.3.3.3 [110/65] via 172.12.123.3, 00:00:55, Serial0We'll now redistribute these routes into RIP on R1. Remember the "subnets" option we talked about in the first part of this tutorial? There is no such option when redistributing OSPF routes into RIP, as IOS Help shows us.R1(config)#router ripR1(config-router)#redistribute ospf 1 ? match Redistribution of OSPF routes metric Metric for redistributed routes route-map Route map reference vrf VPN Routing/Forwarding Instance R1(config-router)#redistribute ospf 1The routes have been redistributed into RIP with the redistribute ospf 1 command. (The "1" is the OSPF process number.) Let's look at R5 and see the results.R5#show ip route ripR5#The routes aren't there, but we didn't get a warning from the router that we needed to do anything else. What is the problem?The problem is that RIP requires a seed metric to be specified when redistributing routes into that protocol. A seed metric is a "starter metric" that gives the RIP process a metric it can work with. The OSPF metric of cost is incomprehensible to RIP, since RIP's sole metric is hop count. We've got to give RIP a metric it understands when redistributing routes into that protocol, so let's go back to R1 and do so.R1(config)#router ripR1(config-router)#no redistribute ospf 1R1(config-router)#redistribute ospf 1 metric 2R5 now sees the routes. Note that the metric contained in the brackets is the seed metric.R5#show ip route rip 34.0.0.0/32 is subnetted, 1 subnetsR 34.3.3.3 [120/2] via 100.1.1.1, 00:00:24, Ethernet0 35.0.0.0/32 is subnetted, 1 subnetsR 35.3.3.3 [120/2] via 100.1.1.1, 00:00:24, Ethernet0 33.0.0.0/32 is subnetted, 1 subnetsR 33.3.3.3 [120/2] via 100.1.1.1, 00:00:24, Ethernet0If you read the previous tutorial, you may have noticed that we did not specify a seed metric for OSPF. OSPF does not require a seed metric to be set during redistribution. You also noticed that the router did tell us that there might be a problem when we left the "subnets" option out of RIP>OSPF redistribution, but the router didn't tell us anything about a seed metric when we performed OSPF>RIP redistribution. This is a detail you must know by heart in order to make your route redistribution successful!

Cisco CCNP / BCMSN Exam Tutorial: Configuring CGMP On Routers & Switches

If a Layer Two switch doesn't have the capabilities to run IGMP Snooping, it will be able to run CGMP - Cisco Group Membership Protocol. CGMP allows the multicast router to work with the Layer Two switch to eliminate unnecessary multicast forwarding. CGMP will be enabled on both the multicast router and the switch, but the router's going to do all the work. The router will be sending Join and Leave messages to the switch as needed. PIM must be running on the router interface facing the switch before enabling CGMP, as you can see:R1(config)#int e0R1(config-if)#ip cgmp WARNING: CGMP requires PIM enabled on interfaceR1(config-if)#ip pim sparseR1(config-if)#ip cgmpWhen CGMP is first enabled on both the multicast router and switch, the router will send a CGMP Join message, informing the switch that a multicast router is now connected to it. This particular CGMP Join will contain a Group Destination Address (GDA) of 0000.0000.0000 and the MAC address of the sending interface. The GDA is used to identify the multicast group, so when this is set to all zeroes, the switch knows this is an introductory CGMP Join, letting the switch know that the multicast router is online.The switch makes an entry in its MAC table that this router can be found off the port that the CGMP Join came in on. The router will send a CGMP Join to the switch every minute to serve as a keepalive.A workstation connected to the switch on port 0/5 now wishes to join multicast group 225.1.1.1. The Join message is sent to the multicast router, but first it will pass through the switch. The switch will do what you'd expect it to do - read the source MAC address and make an entry for it in the MAC address table as being off port fast 0/5 if there's not an entry already there. (Don't forget that the MAC address table is also referred to as the CAM table or the bridging table.)The router will then receive the Join request, and send a CGMP Join back to the switch. This CGMP Join will contain both the multicast group's MAC address and the requesting host's MAC address. Now the switch knows about the multicast group 225.1.1.1 and that a member of that group is found off port fast 0/5. In the future, when the switch receives frames destined for that multicast group, the switch will not flood the frame as it would an unknown multicast. Instead, the switch will forward a copy of the frame to each port that it knows leads to a member of the multicast group.Two major benefits of CGMP are the explicit Join and Leave Group messages. In the next part of this BCMSN exam tutorial, well take a look at the Leave Group messages.

Cisco CCNA / CCNP Certification Exam: Caller ID Screening And Callback

As a CCNA and/or CCNP candidate, you've got to be able to spot situations where Cisco router features can save your client money and time. For example, if a spoke router is calling a hub router and the toll charges at the spoke site are higher than that of the hub router, having the hub router hang up initially and then call the spoke router back can save the client money (and make you look good!) A popular method of doing this is using PPP callback, but as we all know, it's a good idea to know more than one way to do things in Cisco World! A lesser-known but still effective method of callback is Caller ID Screening & Callback. Before we look at the callback feature, though, we need to know what Caller ID Screening is in the first place!This feature is often referred to simply as "Caller ID", which can be a little misleading if you've never seen this service in operation before. To most of us, Caller ID is a phone service that displays the source phone number of an incoming call. Caller ID Screening has a different meaning, though. Caller ID Screening on a Cisco router is really another kind of password - it defines the phone numbers that are allowed to call the router. The list of acceptable source phone numbers is created with the isdn caller command. Luckily for us, this command allows the use of x to specify a wildcard number. The command isdn caller 555xxxx results in calls being accepted from any 7-digit phone number beginning with 555, and rejected in all other cases. We'll configure R2 to do just that and then send a ping from R1 to R2. To see the results of the Caller ID Screening, debug dialer will be run on R1 before sending the ping. Ive edited this output, since the output you see here will be repeated fire times once for each ping packet.R2(config-if)#isdn caller 555xxxxR1#debug dialerDial on demand events debugging is onR1#ping 172.12.12.2Type escape sequence to abort.Sending 5, 100-byte ICMP Echos to 172.12.12.2, timeout is 2 seconds:03:30:25: BR0 DDR: Dialing cause ip (s=172.12.12.1, d=172.12.12.2)03:30:25: BR0 DDR: Attempting to dial 8358662.Success rate is 0 percent (0/5)R1 doesn't give us any hints as to what the problem is, but we can see that the pings definitely aren't going through. On R2, show dialer displays the number of screened calls.R2#show dialerBRI0 - dialer type = ISDNDial String Successes Failures Last DNIS Last status8358661 1 0 00:03:16 successful7 incoming call(s) have been screened.0 incoming call(s) rejected for callback.The callback option mentioned in the last line shown above enables the router to reject a phone call, and then call that router back seconds later.R2 will now be configured to initially hang up on R1, and then call R1 back. R2(config-if)#isdn caller 8358661 callbackR1 will now ping R2. The pings aren't returned, but seconds later R2 calls R1 back.R1#ping 172.12.12.2Success rate is 0 percent (0/5)R1#03:48:12: BRI0: wait for isdn carrier timeout, call id=0x8023R1#03:48:18: %LINK-3-UPDOWN: Interface BRI0:1, changed state to upR1#03:48:18: BR0:1 DDR: dialer protocol upR1#03:48:19: %LINEPROTO-5-UPDOWN: Line protocol on Interface BRI0:1, changed state to upR1#03:48:24: %ISDN-6-CONNECT: Interface BRI0:1 is now connected to 8358662 R2show dialer on R2 shows the reason for the call to R1 is a callback return call.R2#show dialerBRI0 - dialer type = ISDNDial String Successes Failures Last DNIS Last status8358661 3 0 00:00:48 successful7 incoming call(s) have been screened.10 incoming call(s) rejected for callback.BRI0:1 - dialer type = ISDNIdle timer (120 secs), Fast idle timer (20 secs)Wait for carrier (30 secs), Re-enable (15 secs)Dialer state is data link layer upDial reason: Callback return callTime until disconnect 71 secsConnected to 8358661 (R1)The drawback to Caller ID Callback is that not all telco switches support it, so if you have the choice between this and PPP Callback, you're probably better off with PPP Callback. However, it's always a good idea to know more than one way to get things done with Cisco!

Summary

Etherchannels are in use all over the world, as well as on your CCNA and CCNP exams. Learn how to build and support an EC in this tutorial from Chris Bryant, CCIE #12933.