Monday, January 14, 2008

My Cisco Virtual Lab Topology I

I have real Cisco routers and switches but most of the time I rather use virtual devices based on Dynamips. They are portable with my laptop, don't consume additional electricity and provide me with and environment to test features anywhere I go with my laptop. I use it to test QoS, MPLS, IP routing (with OSPF, EIGRP, BGP), gatekeepers configurations, load-balancing, etc. It is just as having the real thing with you.

For example, during my last trip I found myself running 15 routers on my laptop, doing a BGP load balancing configuration validation for a service provider. (Well, I managed to do the job but my laptop's battery was totally drained in little bit more than an hour). But the idea is that, it is a really flexible solution. (BTW, I run Linux so I don't have the memory limitations that the Windows instances have.)

In my case, I have various network files for various topologies. This "Topology 1" is the one the I most commonly use for testing of features, etc. Most of the examples and tips on this site will be tested using this topology as well.

When designing a "physical" virtual topology I try to make them flexible so that I can reuse them on different scenarios without the need to recreate them.

I use the following as my basic Cisco Virtual Lab Topology I
This topology, while simple, is very powerful. With it I can simulate a huge variety of topologies and arrangements. If you look closely you may find hope-and-spoke, star topologies, linear topologies, mixed topologies, etc.

This is the "" file.
autostart = False

workingdir = /path/to/my/workingdir/topology1

image = /path/to/my/image/image_name-extracted.bin
idlepc =
ram = 128
rom = 4
iomem = 5
mmap = False #Force to run in real memory
ghostios = True
exec_area = 64
nvram = 128

model = 3640
console = 2000

slot0 = NM-4E
slot1 = NM-4T

s1/0 = FR 1
s1/1 = R2 s1/1
s1/2 = R2 s1/2
s1/3 = R3 s1/3

e0/0 = SW 11 # Or E0/0 = NIO_linux_eth:eth0
e0/1 = SW 12
e0/2 = SW 13
e0/3 = SW 14

model = 3640
console = 2001

slot0 = NM-4E
slot1 = NM-4T

s1/0 = FR 2
e0/0 = SW 21
e0/1 = SW 22
e0/2 = SW 23
e0/3 = SW 24

model = 3640
console = 2002

slot0 = NM-4E
slot1 = NM-4T

s1/0 = FR 3
s1/1 = R4 s1/1
s1/2 = R4 s1/2

e0/0 = SW 31
e0/1 = SW 32
e0/2 = SW 33
e0/3 = SW 34

model = 3640
console = 2003

slot0 = NM-4E
slot1 = NM-4T

s1/0 = FR 4

e0/0 = SW 41
e0/1 = SW 42
e0/2 = SW 43
e0/3 = SW 44

3:304 = 4:403
2:204 = 4:402
2:203 = 3:302
1:104 = 4:401
1:103 = 3:301
1:102 = 2:201

11 = access 100
12 = access 200
13 = access 300
14 = access 400

21 = access 100
22 = access 200
23 = access 300
24 = access 400

31 = access 100
32 = access 200
33 = access 300
34 = access 400

41 = access 100
42 = access 200
43 = access 300
44 = access 400

For more information visit:



GUI for Dynagen and Dynamips. (Recommended for Windows users):

Dynamips Support Forum:


  1. I've tried your topology with Dynagen, It worked. How can I set VALNs on routers?

    Please show us some routers configuration to understand the topology.(especially VLAN settings)

    Thank you!

  2. what do you mean by (?) in the addressing table?


  3. Hi first to memmori: you don't need to worry about any setting about vlan participating, just enable interfaces which are connected to same vlan for example you want that all routers will be in the same vlan just enable interface e0/0 on all routers and assign ip addresses. the switch in the topology is just like there are 4 virtual swicthes 100,200,300,400.
    To author: i really like this blog it's great :)

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