05-08-2008 06:20 AM - edited 03-05-2019 10:50 PM
Hi All
Just wondering how we are able to get serial ports on a Cisco router to communicate via TCP/IP when there appears to be no MAC address on the serial port of a Cisco Router?
R_ACCESS_1#sh int
FastEthernet0/0 is up, line protocol is up
Hardware is AmdFE, address is 000d.2999.2320 (bia 000d.2999.2320)
Serial0 is up, line protocol is up
Hardware is HD64570
Description: LINK TO MSC2
MTU 1500 bytes, BW 128000 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation X25, loopback not set
Where does the Serial MAC address come from?
Best Regards,
Michael
Solved! Go to Solution.
05-08-2008 07:29 AM
Anyone can correct me if i am wrong.
There is no MAC used in the WAN network.
As MAC works on layer 2 the same way you need to configure the encapsualtion which would work on layer 2.
It can be HDLC or PPP thats the reason how the latyer 2 communcation takes place. If you do not configure the Encapsulation this would not work.
The best example would be the technology Frame-relay its a layer 2 but works on wan without any MAC address.
05-08-2008 06:30 AM
Serial link does not use MAC address.
Encapsulation X25 is the layer 2 protocol which is used in this setup to communicate.
05-08-2008 06:54 AM
Hi There
The snippet of Serial interface configuration I used above was probably a bad axample as this link is indeed configured for XOT. However even if I configure a serial interface with an IP address and connect it to another routers serial interface,
Here is a print out form just such a set up
R1-7206VXR#sh int s1/0
Serial1/0 is up, line protocol is up
Hardware is M8T-X.21
Internet address is 172.16.4.1/24
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, crc 16, loopback not set
R2-7206VXR#sh int s1/0
Serial1/0 is up, line protocol is up
Hardware is M8T-X.21
Internet address is 172.16.4.2/24
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, crc 16, loopback not set
And still there is no MAC address on the interface. So I am wondering how IP connectivity is working?
Even capturing ping traffic between the two routers does not show a MAC address and I am confused as to how this works.
Best Regards,
Michael
05-08-2008 07:29 AM
Anyone can correct me if i am wrong.
There is no MAC used in the WAN network.
As MAC works on layer 2 the same way you need to configure the encapsualtion which would work on layer 2.
It can be HDLC or PPP thats the reason how the latyer 2 communcation takes place. If you do not configure the Encapsulation this would not work.
The best example would be the technology Frame-relay its a layer 2 but works on wan without any MAC address.
05-08-2008 07:39 AM
Hi There
That makes sense. Cheers for the response and clarification.
Best Regards,
Michael
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