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Posts Tagged ‘chris’

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.)
Read the rest of this entry »

In preparing for CCNA exam success, one of the basic steps is to schedule your exam! And when should you do that?

Schedule your exam NOW.

I can hear you now — ” Why should I schedule my exam now? I haven’t started studying yet!”

From experience, I can tell you that this technique works. People complain about timetables and deadlines, but the truth is that people do their best work with a deadline. “Stress” is not the dirty word that we’ve made it out to be. A diamond is only a lump of coal that was put under pressure.

I wish I had a nickel for every time I’ve heard this:

“I’ll schedule my exam when I’m ready.”

You know when “ready” is? For many people, NEVER. I know someone who’s been preparing for his CCNA for years – literally! He’s going to schedule that exam when he’s ready. He’s been getting ready for years!
Read the rest of this entry »

For CCNA exam success, you had better know what split horizon is, how to turn it off, and when to turn it off. Knowing when to turn split horizon off is also important in production networks, because it can cause a hub-and-spoke network to have incomplete routing tables on the spokes.

Split horizon exists for a very good reason – routing loop prevention. The rule of split horizon states that a router cannot send an advertisement for a route out the same interface that it came in on. Split horizon is on by default on all interfaces running RIP, IGRP, and EIGRP.

In this CCNA tutorial, R1 will serve, as the hub and R2 and R3 will be the spokes. We’ll first configure EIGRP over the 172.16.123.0 /24 network, the network connecting the three routers.

R1#conf t

R1(config)#router eigrp 100

R1(config-router)#no auto-summary

R1(config-router)#network 172.12.123.0 0.0.0.255

R2#conf t

R2(config)#router eigrp 100

R2(config-router)#no auto-summary

R2(config-router)#network 172.12.123.0 0.0.0.255

R3#conf t

R3(config)#router eigrp 100

R3(config-router)#no auto-summary

R3(config-router)#network 172.12.123.0 0.0.0.255

Running show ip eigrp neighbor on R1 shows that adjacencies to R2 and R3 are up.

R1#show ip eigrp neighbor

IP-EIGRP neighbors for process 100

H Address Interface Hold Uptime SRTT RTO Q Seq Type

(sec) (ms) Cnt Num

1 172.12.123.3 Se0/0 11 00:02:45 1 5000 0 1

0 172.12.123.2 Se0/0 161 00:03:01 1 5000 0 1

Each router will now advertise its loopback address via EIGRP.

R1#conf t

R1(config)#router eigrp 100

R1(config-router)#network 1.1.1.0 0.0.0.255

R2#conf t

R2(config)#router eigrp 100

R2(config-router)#network 2.2.2.0 0.0.0.255

R3#conf t

R3(config)#router eigrp 100

R3(config-router)#network 3.3.3.0 0.0.0.255

Running show ip eigrp route on each router shows that R1 has a route for both R2’s and R3’s loopback. R2 and R3 will only see R1’s loopback address, and not each other’s. Why?

R1#show ip route eigrp

2.0.0.0/24 is subnetted, 1 subnets

D 2.2.2.0 [90/2297856] via 172.12.123.2, 00:03:19, Serial0/0

3.0.0.0/24 is subnetted, 1 subnets

D 3.3.3.0 [90/2297856] via 172.12.123.3, 00:03:04, Serial0/0

R2#show ip route eigrp

1.0.0.0/24 is subnetted, 1 subnets

D 1.1.1.0 [90/2297856] via 172.12.123.1, 00:03:40, Serial0/0.123

R3#show ip route eigrp

1.0.0.0/24 is subnetted, 1 subnets

D 1.1.1.0 [90/2297856] via 172.12.123.1, 00:05:17, Serial0/0.31
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