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Accessing Serial Interface on CGR through GOS


Both the physical serial Interfaces on the CGR1000 series routers can be connected to the GOS. By default, the serial interfaces are available to IOS only. However, the IOS can be configured to relay the serial information to to a GOS (emulated) serial interface.

The procedure here shows how to map a serial interface to the GOS:

1. Login to IOS and configure the serial interface as follows:

interface Async1/1

    encapsulation relay-line

    async mode dedicated

Configure Async1/2 similarly, if required:

interface Async1/2

    encapsulation relay-line

    async mode dedicated

2. Configure the emulated serial lines between IOS and GOS, and enable relay functionality in IOS.

Configure the following on IOS:

line 1/1

     transport preferred none

     transport input all

     stopbits 1

     speed 115200

relay line 1/1 1/5

The above step will bridge the serial traffic from Async1/1 to GOS interface /dev/ttyS1

Configure relay for the second serial port similarly, if required:

line 1/2

     transport preferred none

     transport input all

     stopbits 1

     speed 115200

relay line 1/2 1/6

The above step will bridge the serial traffic from Async1/2 to GOS interface /dev/ttyS2

3. Read and write to the serial interface from GOS

Read data in the GOS from the serial interface:

cat /dev/ttyS1

Write data to the serial interface from the GOS:

cat data.txt > /dev/ttyS1

Use /dev/ttyS2 for accessing the second serial port (i.e. virtual serial line 1/6 on IOS)

4. (Optional) Bridge data between serial interfaces from the GOS

Use the following CLIs to enable GOS to bridge data between the serial interfaces:

cat /dev/ttyS1 | tee /dev/ttyS2 &

cat /dev/ttyS2 | tee /dev/ttyS1 &

Community Member

Hi Anuj,

thanks for this tutorial.  What about relaying information from the other interfaces to GoS?  Like from WPAN 4/1, or the Fast Ethernet interfaces?  We're wanting to do this at the moment.




Hi Chris,

The GOS has a Layer 3 virtual ethernet connection to Gig0/1 of the IOS. By default, the GOS is configured to request IPv4 DHCP over this virtual interface. IOS can be configured with DHCP server functionality to respond to the GOS DHCP request. . Configuration for the networking between GOS and IOS is described in this document: CGRNetworkConfigGuide.pdf

Similarly, for IPv6 a subnet can be configured in the virtual ethernet link. The Layer 3 routing between CGR interfaces like WPAN4/1, GigabitEthernet, FastEthernet or SVIs and the GOS is performed by the CGR. So effectively, you will have IP connectivity between the GOS and external networks.



Levi Iiams

How can this be done on the C819?


Steve Zhang
Cisco Employee

Hi Gregory,

The sample configuration below shows how to connect serial port s0 on C819 to guest for Modbus RTU Client application. (It uses raw-tcp here. You may use others if necessary.)

interface Serial0

  physical-layer async

  no ip address

  encapsulation raw-tcp


line 7

  raw-socket tcp client 32000


• "" is the host IP address configured in "host ip address" command under IOx submode after you run “show running-config”.

• "32000" is the serial TCP port described in the VM description file (xml from OVA)



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