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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! Read the rest of this entry »

In this CCNA case study, we’ll take some basic switching and trunking theory and put it into action. We have two routers (R2 and R3) along with two switches (SW1 and SW2). R2 is connected to SW1 at fast 0/2, and R3 is connected to SW2 at fast 0/3. Both routers have IP addresses on the 172.12.23.0 /24 network.

For these routers to be able to ping each other, the switches must be able to communicate. These are two 2950 switches, and they’re connected via two crossover cables. Before we worry about the router connectivity, let’s make sure the trunk link is up between the switches with the “show interface trunk” command.

SW2#show interface trunk

Port Mode Encapsulation Status Native vlan

Fa0/11 desirable 802.1q trunking 1

Fa0/12 desirable 802.1q trunking 1

< output truncated for clarity >

The default mode of these switches is for the ports to run in dynamic desirable trunking mode, so we didn’t even need to write a configuration to have the trunk form – it’s already there!

Show vlan brief reinforces the theory that by default, all switch ports are placed into VLAN 1 (except the trunk ports).

R2 and R3’s Ethernet addresses have already been configured, the trunk line is operational, and both ports are in VLAN 1. We’ll ping R2’s Ethernet interface from R3, and then R3’s Ethernet interface from R2 to verify IP connectivity.

R2#ping 172.23.23.3

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.23.23.3, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/8 ms

R3#ping 172.23.23.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.23.23.2, timeout is 2 seconds:
!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/8 ms

With pings, exclamation points indicate IP connectivity, and periods indicate no connectivity.

So we’ve got connectivity! Now let’s see if we still have that connectivity when the ports are placed into different VLANs. Cisco CCNA theory states that devices in different VLANs can’t communicate without the intervention of a Layer 3 device, but let’s see if that’s true by placing R2 into VLAN 23. (VTP is already running on these switches.)
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One of the first things you do when you start studying for the CCNA exam is memorizing a list of port numbers and the protocols that run on those ports. If you’re an experienced networker, you know most of the protocols that are mentioned – DNS, DHCP, FTP, SMTP, and so on. But there’s one protocol that you might not have experience with, but is actually vital for CCNA exam success and success in working with Cisco routers and switches, and that’s TFTP – Trivial File Transfer Protocol.

TFTP is basically FTP’s non-secure relative. There are no passwords, no authentication scheme, no nothing! As someone once told me, “If I’m transferring my files, there’s nothing ‘trivial’ about it.”

Great. So you’re thinking, “What the heck do we use TFTP for, anyway?”

TFTP is used in the Cisco world to perform IOS upgrades and to save configs to a TFTP Server. Cisco routers can themselves serve as TFTP servers, or you can use a workstation to fill that role.

If you needed to copy an IOS image to a router, for example, you could do so easily by connecting your PC to the router’s console port (via a rollover cable, right?). Your PC would need to run TFTP server software. There are quite a few free TFTP server software programs that work quite well – just enter “free tftp server” into Google or your favorite search engine and you’ll see what I mean.

Using TFTP in this fashion is a great way to have backup copies of IOS images or router configs right on your laptop. And take it from me, when the day comes that you need those backups, you’ll be glad you did!
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CCNA exam success depends largely on noticing the details, and this is especially true of configurations involving directly connected serial interfaces. And of course, it’s not enough to notice these details – you’ve got to know what to do about them!

A Cisco router is a DTE by default, but directly connecting two DTEs with a DCE/DTE cable is not enough. In the following example, R1 and R3 are directly connected at their Serial1 interfaces. The line goes up briefly after being opened, but the line protocol goes down after about 30 seconds.

R3(config-if)#int s1

R3(config-if)#ip address 172.12.13.3 255.255.255.0

R3(config-if)#no shutdown

2d18h: %LINK-3-UPDOWN: Interface Serial1, changed state to up

2d18h: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1, changed state to up

R3(config-if)#

2d18h: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1, changed state to down

The problem is that one of the routers needs to act as the DCE in order for the line protocol to come up and stay up. If this were your CCNA / CCNP home lab, you could just go over and look at the DTE/DCE cable to see which router had the DCE end of the cable attached. In this example, though, we don’t have physical access to the routers. How can we tell which router has the DCE end of the cable attached?
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