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Connecting Dynamips/Dynagen router with a real network – in linux

Dynamips/Dynagen supports the interconnection of dynamips router interfaces with a real, in my case ethernet, network cards.  In this case I'm focusing on linux OSs. Within the article "Connecting GNS3 with a VirtualBox host" I'm describing how to do that for GNS3 and Windows 7 environment.


  1. Installed PC/Server with working linux OS (debian Wheezy in my case)
  2. Dynamips/dynagen ready environment with correctly working IOS image (which allow us create a network topology), for example c2691-advipservicesk9-mz.124-15.T13.bin.unp
  3. network card connected to a real network with working connectivity


First, list the real adapters names and connection states within your linux

ip -link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN mode DEFAULT
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT qlen 1000
    link/ether 00:1d:09:f2:7c:47 brd ff:ff:ff:ff:ff:ff
3: eth1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT qlen 1000
    link/ether 00:1d:09:f2:7c:49 brd ff:ff:ff:ff:ff:ff

as we see, the eth0 interface is up.

Then we interconnect virtual router interface with working card adapter. Dynamips tutorial is saying (I'm not sure if the original site is just temporary off or not, so here is the copy of original tutorial):

Dynamips can bridge virtual router interfaces real host interfaces, allowing your virtual network to communicate with the real world. On Linux systems, this is done with the NIO_linux_eth NIO descriptor. For example:

f0/0 = NIO_linux_eth:eth0

this bridges this router’s F0/0 interface to the eth0 interface on the host. Packets that exit f0/0 are dumped out on to the real network through eth0, and return packets are forwarded back to the virtual router instance accordingly.


So, let create a simple dynamips topo with just one router to demonstrate:

autostart = False


        workingdir = /home/segi/IS/mcast/Work
        udp = 30000

                ram = 128
                image = /Topologies/IOSes/c2691-advipservicesk9-mz.124-12.bin.unp
                ghostios = True
                sparsemem = True
                slot1 = NM-4T
                confreg = 0x2102
                idlepc = 0x60a29810

        [[ROUTER R1]]
                model = 2691
                console = 3000
                # Connect f0/0 interface with my eth1 adapter
                f0/0 = NIO_linux_eth:eth0

Now start the topo as the root (see the note at the bottom of the page)

Cisco Router Simulation Platform (version 0.2.11-amd64/Linux stable)
Copyright (c) 2005-2011 Christophe Fillot.
Build date: Mar  5 2014 07:22:36

Local UUID: ace2bfea-68f3-4a9c-a841-758409ca92e6

Hypervisor TCP control server started (port 30000).
Reading configuration file...

Shutdown in progress...
Shutdown completed.
Network successfully loaded

Dynagen management console for Dynamips and Pemuwrapper 0.11.0
Copyright (c) 2005-2007 Greg Anuzelli, contributions Pavel Skovajsa

and start the R1 router within dynagen with start R1 command

=> start R1
CPU0: carved JIT exec zone of 64 Mb into 2048 pages of 32 Kb.
NVRAM is empty, setting config register to 0x2142
C2691 instance 'R1' (id 0):
  VM Status  : 0
  RAM size   : 128 Mb
  NVRAM size : 112 Kb
  IOS image  : /Topologies/IOSes/c2691-advipservicesk9-mz.124-12.bin.unp

Loading ELF file '/Topologies/IOSes/c2691-advipservicesk9-mz.124-12.bin.unp'...
ELF entry point: 0x80008000

C2691 'R1': starting simulation (CPU0 PC=0xffffffffbfc00000), JIT enabled.
100-VM 'R1' started
=> list
Name       Type       State      Server          Console
R1         2691       running    localhost:30000 3000

Now we are able to connect to the R1 (telnet localhost 3000 in my case) and configure router fastEthernet interface with static or dynamic IP address

Router#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#int fa 0/0
Router(config-if)#no sh
Router(config-if)#ip address dhcp
*Mar  1 00:02:08.723: %DHCP-6-ADDRESS_ASSIGN: Interface FastEthernet0/0 assigned DHCP address, mask, hostname Router
Router(config-if)#do sh ip int brief
Interface                  IP-Address      OK? Method Status                Protocol
FastEthernet0/0    YES DHCP   up                    up
FastEthernet0/1            unassigned      YES unset  administratively down down
Serial1/0                  unassigned      YES unset  administratively down down
Serial1/1                  unassigned      YES unset  administratively down down
Serial1/2                  unassigned      YES unset  administratively down down
Serial1/3                  unassigned      YES unset  administratively down down

and finally we check connectivity pinging some real IP address within a real network, in my case


Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/8/16 ms



1) If the dynagen /dynamips return following message

eth_init_socket: socket: Operation not permitted
*** Warning:  Connecting R1 f0/0 to NIO_linux_eth:eth1 resulted in:
        206-unable to create Linux raw ethernet NIO

Check your linux permissions under which you are running Dynagen, because using gen_eth and linux_eth NIO you must run the dynamips process with the "root" account.


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