Please note, this article represents the very basics of Dynamips. There are several add-on projects that have made Dynamips much more user friendly for the average person to configure. However, there is an old saying, “You must walk before you can run” that I truly believe in. So, this explanation will at least give you some root information on how Dynamips works by itself (walking). You will most likely run Dynamips using a ‘front end’ such as Dynagen or GNS3(running) which will be covered in other articles.

In this initial explanation, we will run a single virtual 7200 router instance that will have an Ethernet interface bridged with a network adapter on the host PC. By doing this, the host PC will be able to communicate to the virtual router just like it was a real router on a real network.

The first thing needed is to determine the PCAP string that represents the network adapter to be bridged with the virtual router interface. To do this run the dynamips executable with just a ‘-e’ option.

C:\Program Files\Dynamips>dynamips -e
Cisco Router Simulation Platform (version 0.2.8-RC1-x86)
Copyright (c) 2005-2007 Christophe Fillot.
Build date: Sep 7 2007 17:17:20

Network device list:

rpcap://\Device\NPF_{3A61C8A2-3B20-4C04-880D-C24930E29609} : Network adapter ‘Intel(R) PRO/1000 MT Mobile Connection - Deterministic Network Enhancer Miniport’ on local host
rpcap://\Device\NPF_{6BEED806-4E3F-41F9-A5E6-9E558ECFB2E3} : Network adapter ‘MS LoopBack Driver’ on local host
rpcap://\Device\NPF_{FCE28766-936D-4D4B-A534-CC9D50B477C5} : Network adapter ‘Intel(R) PRO/Wireless 2200BG Network Connectio’ on local host

The Windows interface we want to use for communication with the virtual router interface is the MS Loopback Driver. So the next step is to create a switch.cfg file, this will define the properties of the virtual switch.

IF:E0:udp:10001:127.0.0.1:10000
IF:E1:gen_eth:\Device\NPF_{6BEED806-4E3F-41F9-A5E6-9E558ECFB2E3}

ACCESS:E0:4
ACCESS:E1:4

The contents of this file will define the makeup of the virtual switch. In this particular virtual switch, there are two interfaces: E0 and E1. The virtual switch interface E0 will be sourced locally using udp port 10001 and will connect to port 10000, also residing on the localhost. The virtual switch interface E1 will be mapped to the Windows loopback adapter. Both ports are put in the same vlan, which is vlan 4 in this particular example. Once the file is created, you can run Dynamips like so:

dynamips-wxp.exe -X -i 996 -t npe-400 -r 256 -p 0:C7200-IO-FE -s 0:0:udp:10000:127.0.0.1:10001 c7200-spservicesk9-mz.124-11.T1.image -E switch.cfg

The above command string starts a single Dynamips 7200 instance with a C7200-IO card containing a single FastEthernet adapter, which will be FastEthernet0/0 inside the IOS. The -s option says take the adapter in slot0:port0 and map it’s input locally to udp port 10000 and direct it’s output traffic to udp port 10001 on the localhost. You will notice this is just the opposite of what is defined in the switch configuration file. Below is what you will see after running the command string above:

Cisco Router Simulation Platform (version 0.2.8-RC2-x86)
Copyright (c) 2005-2007 Christophe Fillot.
Build date: Oct 14 2007 10:54:51

Instance ID set to 996.
Virtual RAM size set to 256 MB.
IOS image file: ..\ios\c7200-spservicesk9-mz.124-11.T1.image

ILT: loaded table "mips64j" from cache.
ILT: loaded table "mips64e" from cache.
ILT: loaded table "ppc32j" from cache.
ILT: loaded table "ppc32e" from cache.
CPU0: carved JIT exec zone of 16 Mb into 512 pages of 32 Kb.
C7200 instance 'default' (id 996):
  VM Status  : 0
  RAM size   : 256 Mb
  IOMEM size : 0 Mb
  NVRAM size : 128 Kb
  NPE model  : npe-400
  Midplane   : vxr
  IOS image  : ..\ios\c7200-spservicesk9-mz.124-11.T1.image

Loading ELF file '..\ios\c7200-spservicesk9-mz.124-11.T1.image'...
ELF entry point: 0x80008000

C7200 'default': starting simulation (CPU0 PC=0xffffffffbfc00000), JIT enabled.
ROMMON emulation microcode.

Launching IOS image at 0x80008000...
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Software clause at DFARS sec. 252.227-7013.

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San Jose, California 95134-1706

Cisco IOS Software, 7200 Software (C7200-SPSERVICESK9-M), Version 12.4(11)T1, RE
LEASE SOFTWARE (fc5)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2007 by Cisco Systems, Inc.
Compiled Thu 25-Jan-07 19:57 by prod_rel_team
Image text-base: 0x60009084, data-base: 0x62B1A000

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If you require further assistance please contact us by sending email to
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Cisco 7206VXR (NPE400) processor (revision A) with 245760K/16384K bytes of memory.
Processor board ID 4294967295
R7000 CPU at 150MHz, Implementation 39, Rev 2.1, 256KB L2, 512KB L3 Cache
6 slot VXR midplane, Version 2.1

Last reset from power-on

PCI bus mb0_mb1 (Slots 0, 1, 3 and 5) has a capacity of 600 bandwidth points.
Current configuration on bus mb0_mb1 has a total of 200 bandwidth points.
This configuration is within the PCI bus capacity and is supported.

PCI bus mb2 (Slots 2, 4, 6) has a capacity of 600 bandwidth points.
Current configuration on bus mb2 has a total of 0 bandwidth points
This configuration is within the PCI bus capacity and is supported.

Please refer to the following document "Cisco 7200 Series Port Adaptor
Hardware Configuration Guidelines" on Cisco.com <http://www.cisco.com>
for c7200 bandwidth points oversubscription and usage guidelines.

1 FastEthernet interface
125K bytes of NVRAM.

65536K bytes of ATA PCMCIA card at slot 0 (Sector size 512 bytes).
8192K bytes of Flash internal SIMM (Sector size 256K).
% Crashinfo may not be recovered at bootflash:crashinfo
% This file system device reports an error

Press RETURN to get started!

*Jan  6 23:23:01.927: %LINEPROTO-5-UPDOWN: Line protocol on Interface VoIP-Null0
, changed state to up
*Jan  6 23:23:01.931: %LINK-3-UPDOWN: Interface FastEthernet0/0, changed state to up
*Jan  6 23:23:03.047: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthern
et0/0, changed state to up
*Jan  6 23:23:03.531: %SYS-5-CONFIG_I: Configured from memory by console
*Jan  6 23:23:03.855: %SYS-5-RESTART: System restarted --
Cisco IOS Software, 7200 Software (C7200-SPSERVICESK9-M), Version 12.4(11)T1, RELEASE SOFTWARE (fc5)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2007 by Cisco Systems, Inc.
Compiled Thu 25-Jan-07 19:57 by prod_rel_team
*Jan  6 23:23:04.183: %SNMP-5-COLDSTART: SNMP agent on host Router is undergoing a cold start
Router>

Our loopback IP address is statically defined on the Windows PC as 10.1.100.20, so we will ping it from the IOS command prompt:

Router>en

Router#sh ip int brief

Interface           IP-Address    OK?    Method    Status    Protocol

FastEthernet0/0     10.1.100.1    YES    NVRAM     up        up

Router#ping 10.1.100.20

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.1.100.20, timeout is 2 seconds:
.!!!!
Success rate is 80 percent (4/5), round-trip min/avg/max = 28/68/92 ms
Router#

As you can see, we have successfully setup an single virtual router instance using Dynamips and have configured it to successfully communicate to an interface on the host Windows PC.