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.

Prerequisities

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

Procedures

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 http://www.dynagen.org/tutorial.htm 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

[localhost:30000]

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

        [[2691]]
                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>ena
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 158.193.152.59, mask 255.255.255.0, hostname Router
Router(config-if)#do sh ip int brief
Interface                  IP-Address      OK? Method Status                Protocol
FastEthernet0/0            158.193.152.59  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

ping 158.193.152.2

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 158.193.152.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/8/16 ms

Working.

Note:

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.