Command:

debug serial interface


Mode:

Router#


Syntax:

debug serial interface

no debug serial interface

Syntax Description:

This command has no arguments or keywords.

Command Description:

 

To display information on a serial connection failure, use the debug serial interface privileged EXEC

command. The no form of this command disables debugging output.

 

If the show interface serial EXEC command shows that the line and protocol are down, you can use the

debug serial interface command to isolate a timing problem as the cause of a connection failure. If the

keepalive values in the mineseq, yourseen, and myseen fields are not incrementing in each subsequent

line of output, there is a timing or line problem at one end of the connection.

 

Caution Although the debug serial interface command typically does not generate a substantial amount of

output, nevertheless use it cautiously during production hours. When SMDS is enabled, for example,

it can generate considerable output.

The output of the debug serial interface command can vary, depending on the type of WAN configured

for an interface: Frame Relay, HDLC, HSSI, SMDS, or X.25. The output also can vary depending on the

type of encapsulation configured for that interface. The hardware platform also can affect debug serial

interface output.


Example:

The following sections show and describe sample debug serial interface output for various

configurations.

Debug Serial Interface for Frame Relay Encapsulation

 

The following message is displayed if the encapsulation for the interface is Frame Relay (or HDLC) and

the router attempts to send a packet containing an unknown packet type:

Illegal serial link type code xxx

 

Debug Serial Interface for HDLC

The following is sample output from the debug serial interface command for an HDLC connection

when keepalives are enabled. This output shows that the remote router is not receiving all the keepalives

the router is sending. When the difference in the values in the myseq and mineseen fields exceeds three,

the line goes down and the interface is reset.

Table 160 describes the significant fields.

router# debug serial interface

Serial1: HDLC myseq 636119, mineseen 636119, yourseen 515032, line up

Serial1: HDLC myseq 636120, mineseen 636120, yourseen 515033, line up

Serial1: HDLC myseq 636121, mineseen 636121, yourseen 515034, line up

Serial1: HDLC myseq 636122, mineseen 636122, yourseen 515035, line up

Serial1: HDLC myseq 636123, mineseen 636123, yourseen 515036, line up

Serial1: HDLC myseq 636124, mineseen 636124, yourseen 515037, line up

Serial1: HDLC myseq 636125, mineseen 636125, yourseen 515038, line up

Serial1: HDLC myseq 636126, mineseen 636126, yourseen 515039, line up

Serial1: HDLC myseq 636127, mineseen 636127, yourseen 515040, line up

Serial1: HDLC myseq 636128, mineseen 636127, yourseen 515041, line up

Serial1: HDLC myseq 636129, mineseen 636129, yourseen 515042, line up

Serial1: HDLC myseq 636130, mineseen 636130, yourseen 515043, line up

Serial1: HDLC myseq 636131, mineseen 636130, yourseen 515044, line up

Serial1: HDLC myseq 636132, mineseen 636130, yourseen 515045, line up

Serial1: HDLC myseq 636133, mineseen 636130, yourseen 515046, line down

Serial1: HDLC myseq 636127, mineseen 636127, yourseen 515040, line up

Serial1: HDLC myseq 636128, mineseen 636127, yourseen 515041, line up

Serial1: HDLC myseq 636129, mineseen 636129, yourseen 515042, line up


Misconceptions:

           None.


Related Commands:

            None. 


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