Enable Virtual LAN (VLAN) to seperate two Layer 2 worlds (CNA-03-001)

CCNA Exploration 4.0, Semester 3, "Enable Virtual LAN (VLAN) to seperate two Layer 2 worlds" Packet Tracer 5.0 practice file (CNA-03-001).

• CNA-03-001.pkt, (Backup Link)
• CNA-03-001-sol.pkt, (Backup Link)

Virtual LAN (VLAN) service, for short, is to make one physical switch look like and used like multiple logical switches. This is indeed a "virtualization" of Ethernet switches, just like the concept of "virtualization computing" now. "Virtualization computing" is quite a hot topic recently. If you have used VMWare or Microsoft Virtual PC, you would know what virtualization is!

Virtual LAN <---> Virtual Machine

I will talk more about "Virtualization" in the future! Let's go back to the main topic.

This practice is to get familiar with assigning different switch ports to different VLANs.

According to the requirements displayed in the diagram, once we assign the switch ports connecting to PC1 and PC3 to VLAN 10, and then assign switch ports connecting to PC2 and PC4 to VLAN 20, our jobs are done. Two worlds are seperated!

To assign switch port to designated VLAN we can configure like the this: (Suppose the designated VLAN number is 10)

interface FastEthernet 0/1
 switchport access vlan 10

Observe and solve Classful addressing problem, using OSPF (CNA-02-007)

CCNA Exploration 4.0, Semester 2, "Observe and solve Classful addressing problem, using OSPF" Packet Tracer 5.0 practice file (CNA-02-007).

• CNA-02-007.pkt, (Backup Link)
• CNA-02-007-sol.pkt, (Backup Link)

I like to use OSPF because I do not have to worry about any "Classful" problem at all: there is no "Classful" function in its design and no backward compatibility burdens. No "no auto-summary" command in OSPF!

As long as OSPF is running fine, all routes would also be fine!

R2>sh ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
       * - candidate default, U - per-user static route, o - ODR
       P - periodic downloaded static route

Gateway of last resort is not set

     10.0.0.0/24 is subnetted, 2 subnets
O       10.1.1.0 [110/65] via 172.30.2.1, 00:00:24, Serial0/0/0
O       10.2.2.0 [110/65] via 192.168.4.1, 00:00:24, Serial0/0/1
     172.30.0.0/24 is subnetted, 3 subnets
O       172.30.1.0 [110/65] via 172.30.2.1, 00:00:24, Serial0/0/0
C       172.30.2.0 is directly connected, Serial0/0/0
C       172.30.3.0 is directly connected, FastEthernet0/0
C    192.168.4.0/24 is directly connected, Serial0/0/1
O    192.168.5.0/24 [110/65] via 192.168.4.1, 00:00:24, Serial0/0/1
R2>

Observe and solve Classful addressing problem, using EIGRP (CNA-02-006)

CCNA Exploration 4.0, Semester 2, "Observe and solve Classful addressing problem, using EIGRP" Packet Tracer 5.0 practice file (CNA-02-006).

• CNA-02-006.pkt, (Backup Link)
• CNA-02-006-wrong-sol.pkt, (Backup Link)
• CNA-02-006-final-sol.pkt, (Backup Link)

I choose to re-use the same network diagram and addressing as the previous example. Many of us might think when we just dump the old RIPs and use the modern ones such as EIGRP, the Classful addressing problem would be solved by itself. However, since EIGRP is an "Enhanced" version of "IGRP", to minimize impact to customers Cisco still set its behaviors to "Classful" by default. It's not enough to only enable EIGRP! See below in the wrong solution (Backup Link), the problem is the same as before:

R2>show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
       * - candidate default, U - per-user static route, o - ODR
       P - periodic downloaded static route

Gateway of last resort is not set

D    10.0.0.0/8 [90/2172416] via 172.30.2.1, 00:00:10, Serial0/0/0
                [90/2172416] via 192.168.4.1, 00:00:10, Serial0/0/1
     172.30.0.0/16 is variably subnetted, 4 subnets, 2 masks
D       172.30.0.0/16 is a summary, 00:00:10, Null0
D       172.30.1.0/24 [90/2172416] via 172.30.2.1, 00:00:10, Serial0/0/0
C       172.30.2.0/24 is directly connected, Serial0/0/0
C       172.30.3.0/24 is directly connected, FastEthernet0/0
C    192.168.4.0/24 is directly connected, Serial0/0/1
D    192.168.5.0/24 [90/2172416] via 192.168.4.1, 00:00:10, Serial0/0/1
R2>

The key is to turn off "Classful behaviors" by manually adding "no auto-summary" command!

router eigrp 1
 network 172.30.0.0
 network 192.168.4.0
 no auto-summary

After this command, the correct result is now like this (Backup Link):

R2>show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
       * - candidate default, U - per-user static route, o - ODR
       P - periodic downloaded static route

Gateway of last resort is not set

     10.0.0.0/24 is subnetted, 2 subnets
D       10.1.1.0 [90/2172416] via 172.30.2.1, 00:00:35, Serial0/0/0
D       10.2.2.0 [90/2172416] via 192.168.4.1, 00:00:34, Serial0/0/1
     172.30.0.0/24 is subnetted, 3 subnets
D       172.30.1.0 [90/2172416] via 172.30.2.1, 00:00:35, Serial0/0/0
C       172.30.2.0 is directly connected, Serial0/0/0
C       172.30.3.0 is directly connected, FastEthernet0/0
C    192.168.4.0/24 is directly connected, Serial0/0/1
D    192.168.5.0/24 [90/2172416] via 192.168.4.1, 00:00:34, Serial0/0/1
R2>

How to "Resign" your Router role as DR/BDR in OSPF without clearing OSPF process?

Cherry Flower (DSCN0694),
originally uploaded by Li-Ji.

In Cisco IOS, just change that interface priority to zero (0), then it quits the role of DR/BDR immediately.

interface FastEthernet0/0
 ip ospf priority 0

Solving Classful addressing problem, using RIP (CNA-02-005)

CCNA Exploration 4.0, Semester 2, "Solving Classful addressing problem, using RIP" Packet Tracer 5.0 practice file (CNA-02-005).

• CNA-02-005.pkt, (Backup Link)
• CNA-02-005-wrong-sol.pkt, (Backup Link)
• CNA-02-005-final-sol.pkt, (Backup Link)

In this example, the IP addressing scheme is only allowed in the our current new "Classless" world. That's why any old "Classful" routing protocols will not work.

The problem is at the routing entries in R2's routing table. Two "10.0.0.0/8" entries will be there. This is a typical "Classful" world behavior: when advertising routing information to other "classful network address"'s router, all subnet routes will be summarized into one route, which is exactly the same as your own "classful network address".

In this case, the "classful network address" is exactly "10.0.0.0/8".  The peer router is R2 and is not within this classful network address.

That's why 50% of packets destined for either 10.1.1.0/24 or 10.2.2.0/24 would go to the wrong router and get dropped!

Here is the wrong routing table, by using RIP version 1 (CNA-02-005-wrong-sol.pkt, Backup Link):

R2>show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
       * - candidate default, U - per-user static route, o - ODR
       P - periodic downloaded static route

Gateway of last resort is not set

R    10.0.0.0/8 [120/1] via 192.168.4.1, 00:00:17, Serial0/0/1
                [120/1] via 172.30.2.1, 00:00:14, Serial0/0/0
     172.30.0.0/24 is subnetted, 3 subnets
R       172.30.1.0 [120/1] via 172.30.2.1, 00:00:14, Serial0/0/0
C       172.30.2.0 is directly connected, Serial0/0/0
C       172.30.3.0 is directly connected, FastEthernet0/0
C    192.168.4.0/24 is directly connected, Serial0/0/1
R    192.168.5.0/24 [120/1] via 192.168.4.1, 00:00:17, Serial0/0/1
R2>

Therefore, we can only implement "Classless" protocols, such as RIP version 2. (CNA-02-005-final-sol.pkt, Backup Link). Also remember to add "no auto-summary" command to disable RIPv2's "Classful behavior"!

R2>show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
       * - candidate default, U - per-user static route, o - ODR
       P - periodic downloaded static route

Gateway of last resort is not set

     10.0.0.0/24 is subnetted, 2 subnets
R       10.1.1.0 [120/1] via 172.30.2.1, 00:00:12, Serial0/0/0
R       10.2.2.0 [120/1] via 192.168.4.1, 00:00:12, Serial0/0/1
     172.30.0.0/24 is subnetted, 3 subnets
R       172.30.1.0 [120/1] via 172.30.2.1, 00:00:12, Serial0/0/0
C       172.30.2.0 is directly connected, Serial0/0/0
C       172.30.3.0 is directly connected, FastEthernet0/0
C    192.168.4.0/24 is directly connected, Serial0/0/1
R    192.168.5.0/24 [120/1] via 192.168.4.1, 00:00:12, Serial0/0/1
R2>