Yes, it is cisco propritary protocol. B/C Cisco add nice feature on it. So, it won't comparible with other generic HDLC protocol.

What features are added ?

- Keepalive
- SLARP (Serial Link Address Resolution Protocol)
- Compression
- Performance (header 7-12)

[Cisco Router1]

R1#sh run int serial 3/1
Building configuration...

Current configuration : 112 bytes
!
interface Serial3/1
description to R2
ip address 100.100.100.1 255.255.255.252
serial restart-delay 0
end

 

 

[Cisco Router2]

R2#sh run int serial 3/1
Building configuration...

Current configuration : 112 bytes
!
interface Serial3/1
description to R1
ip address 100.100.100.2 255.255.255.252
serial restart-delay 0
end

 

 

 

[Cisco Router1 with compression]

R1#sh run int serial 3/1
Building configuration...

Current configuration : 127 bytes
!
interface Serial3/1
description to R2
ip address 100.100.100.1 255.255.255.252
compress stac <-- it makes fast link, but CPU intensive command
serial restart-delay 0
end

 

 

[Cisco Router2 with compression]

R1#sh run int serial 3/1
Building configuration...

Current configuration : 127 bytes
!
interface Serial3/1
description to R1
ip address 100.100.100.2 255.255.255.252
compress stac <-- Both sides need to be configred.
serial restart-delay 0
end

 

 

 

[Debug HDLC]

<font size="2" face="Tahoma ">R2#<font color="#ff0000">debug serial interface</font></font> 

<font size="2" face="Tahoma ">Serial network interface debugging is on</font>

<font size="2" face="Tahoma ">R2#</font> 

<font size="2" face="Tahoma ">*Mar  1 00:57:04.103: Serial3/1: HDLC myseq 341, mineseen 341*, yourseen 10, line up</font>

<font size="2" face="Tahoma ">R2#</font> 

<font size="2" face="Tahoma ">*Mar  1 00:57:14.103: Serial3/1: HDLC myseq 342, mineseen 341, yourseen 10, line up</font>

<font size="2" face="Tahoma ">R2#</font> 

<font size="2" face="Tahoma ">*Mar  1 00:57:24.103: Serial3/1: HDLC myseq 343, mineseen 341, yourseen 10, line up</font>

<font size="2" face="Tahoma ">R2#</font> 

<font size="2" face="Tahoma ">*Mar  1 00:57:34.119: Serial3/1: HDLC myseq 344, mineseen 341, yourseen 10, line down</font>

<font size="2" face="Tahoma ">*Mar  1 00:57:35.119: %LINEPROTO-5-UPDOWN: Line protocol on  Serial3/1, changed state to down</font>

<font size="2" face="Tahoma ">R2#</font> 

<font size="2" face="Tahoma ">*Mar  1 00:57:44.103: Serial3/1: HDLC myseq 345, mineseen 341, yourseen 10, line down</font>

<font size="2" face="Tahoma ">R2#u all</font> 

<font size="2" face="Tahoma ">All possible debugging has been turned off</font>

<font size="2" face="Tahoma ">R2#</font> 

 

 

 

 

 

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