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I'm pretty new to networking and still learning CCNA stuff. I'm reading a book and as I understand, when you are connecting two routers using a serial line, one router is considered DCE and the other is DTE. The DCE side should set clock rate in order to make them communicate successfully. Is my understanding correct? I did some test in gns3 and it seems my understanding is wrong. Below is the topology I have.

enter image description here

This is the configuration for R1.

R1#sh run | s interface Serial2/0
interface Serial2/0
 ip address 192.168.1.1 255.255.255.0
 serial restart-delay 0
R1#

This is the configuration for R2.

R2#sh run | s interface Serial2/0
interface Serial2/0
 ip address 192.168.1.2 255.255.255.0
 serial restart-delay 0
R2#

As you can see, I haven't set clock rate for both of them. But I can successfully ping from both ends.

R1#ping 192.168.1.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/17/36 ms
R1#
R2#ping 192.168.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/13/32 ms
R2#p

Is there anything wrong with my understanding or my testing?

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    Because there's a default clock rate.
    – Ricky
    Feb 7 at 19:14
  • @Ricky Then in this case, which end is DCE and which is DTE? Feb 8 at 1:11
  • 2
    Both/neither. GNS3 is doing the tx/rx cross-connect for you. In the Real World(tm), you have to do that yourself ("null modem" style cables, etc.)
    – Ricky
    Feb 8 at 2:31
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Since both network are directly connected networks . So routers are able to ping each other . Coming to clockrate when clock rate is not configured on either router it' picks default clockrate set by manufacturer.

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