BCMSN exam success and earning your CCNP certification requires you to add to your knowledge of VLAN configuration.
When you studied for your CCNA exam, you learned how to place ports into a VLAN and what the purpose of VLANs was, but you may not be aware that there are two types of VLAN membership. To pass the BCMSN exam, you must know the details of both types.
In this tutorial, we´ll take a look at the VLAN type you are most familiar with, the “static VLAN”. As you know, VLANs are a great way to create smaller broadcast domains in your network. Host devices connected to a port belonging to one VLAN will receive broadcasts and multicasts only if they were originated by another host in that same VLAN. The drawback is that without the help of a Layer 3 switch or a router, inter-VLAN communication cannot occur.
The actual configuration of a static VLAN is simple enough. In this example, by placing switch ports 0/1 and 0/2 into VLAN 12, the only broadcasts and multicasts hosts connected to those ports will receive are the ones transmitted by ports in VLAN 12.
SW1(config)#int fast 0/1
SW1(config-if)#switchport mode access
SW1(config-if)#switchport access vlan 12
% Access VLAN does not exist. Creating vlan 12
SW1(config-if)#int fast 0/2
SW1(config-if)#switchport mode access
SW1(config-if)#switchport access vlan 12
One of the many things I love about Cisco switches and routers is that if you have forgotten to do something, the Cisco device is generally going to remind you or in this case actually do it for you. I placed port 0/1 into a VLAN that did not yet exist, so the switch created it for me!
There are two commands needed to place a port into a VLAN. By default, these ports are running in dynamic desirable trunking mode, meaning that the port is actively attempting to form a trunk with a remote switch in order to send traffic between the two switches. The problem is that a trunk port belongs to all VLANs by default, and we want to put this port into a single VLAN only. To do so, we run the switchport mode access command to make the port an access port, and access ports belong to one and only one VLAN. After doing that, we placed the port into VLAN 12 with the switchport access vlan 12 command. Running the switchport mode access command effectively turns trunking off on that port.
The hosts are unaware of VLANs; they simply assume the VLAN membership of the port they´re connected to. But that´s not quite the case with dynamic VLANs, which we´ll examine in the next part of this BCMSN tutorial.
When you work with computer networks, you´ve got to be continually learning and staying up on the latest technologies and changes in the field. Part of this responsibility is keeping your CCNA current by meeting Cisco´s recertification requirements.
Cisco requires CCNAs to recertify once every three years. While most CCNAs will move on to the CCNP in that time, if you choose not to you must meet certain requirements in order to keep your CCNA valid. Cisco does this to ensure that CCNAs keep their networking knowledge current, which in turn helps the CCNA certification valuable. And that´s exactly what you want, since you worked so hard to earn your certification in the first place!
As of March 2006, there are five different options for recertifying as a CCNA. You can take and pass any of the following exams to renew your CCNA – the CCNA exam itself, the ICND exam, any 642 series exam, any Cisco Qualiied Specialist exam (except the Sales Specialist exams – those don´t count!), or any CCIE Written Qualification exam.
With all these options, there´s an option that´s just right for you. Whether you just want to renew your CCNA or pursue a Specialist, CCNP, or CCIE certification, you can easily renew your CCNA along the way. Just don´t forget that keeping up with Cisco´s latest recertification requirements is your responsibility, and that´s easy to do – just visit Cisco´s “Learning And Events” section on their website. Cisco will tell you what you need to do to keep your certification, but it´s up to you to keep up with certification program changes! Once your certification expires, it’s gone, so get in the habit of visiting Cisco’s website to make sure you’re up to date on important recertification requirements.
Preparing to pass the CCNA exam and earn this important Cisco certification?
Route summarization is just one of the many skills you´ll have to master in order to earn your CCNA. Whether it´s RIP version 2, OSPF, or EIGRP, the CCNA exam will demand that you can flawlessly configure route summarization.
Route summarization isn´t just important for the CCNA exam. It´s a valuable skill to have in the real world as well. Correctly summarizing routes can lead to smaller routing tables that are still able to route packets accurately – what I like to call “concise and complete” routing tables.
The first skill you´ve got to have in order to work with route summarization is binary math; more specifically, you must be able to take multiple routes and come up with both a summary route and mask to advertise to downstream routers. Given the networks 188.8.131.52 /16, 184.108.40.206 /16, 220.127.116.11 /16, and 18.104.22.168 /16, could you quickly come up with both the summary address and mask? All you need to do is break the four network numbers down into binary strings. We know the last two octets will all convert to the binary string 00000000, so in this article we´ll only illustrate how to convert the first and second octet from decimal to binary.
100 16 = 01100100 00010000
100 17 = 01100100 00010001
100 18 = 01100100 00010010
100 19 = 01100100 00010011
To come up with the summary route, just work from left to right and draw a line where the four networks no longer have a bit in common. For these four networks, that point comes between the 14th and 15th bits. This leaves us with this string: 01100100 000100xx. All you need to do is convert that string back to decimal, which gives us 100 for the first octet and 16 for the second. (The two x values are bits on the right side of the line, which aren´t used in calculating the summary route.) Since we know that zero is the value for the last two octets, the resulting summary network number is 22.214.171.124.
But we´re not done! We now have to come up with the summary mask to advertise along with the summary route. To arrive at the summary route, write out a mask in binary with a “1” for every bit to the left of the line we drew previously, and a “0” for every bit to the right. That gives us the following string:
11111111 11111100 00000000 00000000
Converting that to dotted decimal, we arrive at the summary mask 255.252.0.0. The correct summary network and mask to advertise are 126.96.36.199 252.0.0.0.
For the CCNA exam, emphasis is put on knowing how to advertise these summary routes in RIPv2 and EIGRP. For both of these protocols, route summarization happens at the interface level – it´s not configured under the protocol. On the interface that should advertise the summary route, use the command “ip summary-address”. Here are examples of how the above summary route would be configured on ethernet0 in both RIPv2 and EIGRP.
R1(config-if)#ip summary-address rip 188.8.131.52 255.252.0.0
R1(config-if)#ip summary-address eigrp 100 184.108.40.206 255.252.0.0
The main difference between the two is that the EIGRP command must specify the AS number – that´s what the “100” is in the middle of the EIGRP command. Since RIPv2 does not use AS numbers, there´s no additional value needed in the configuration.
For OSPF, the commands differ. If you´re configuring inter-area route summarization, use the “area range” command; if you are summarizing routes that are being redistributed into OSPF, use the summary-address command under the OSPF routing process on the ASBR. Neither of these are interface-level commands.
I speak from experience when I tell you that practice makes perfect on the CCNA exam, especially with binary and summarization questions. The great thing about these questions is that there are no grey areas with these questions – you either know how to do it or you don´t. And with practice and an eye for detail, you can master these skills, pass the exam, and become a CCNA. Here´s to your success!