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Chapter 7
Troubleshooting Serial Line and Frame Relay Connectivity
Serial0(in): Status, myseq 137
Serial1(out): StEnq, myseq 4, yourseen 10, DTE up
Serial1(in): Status, myseq 4
Serial2(out): StEnq, myseq 249, yourseen 249, DTE up
Serial2(in): Status, myseq 249
Serial3(out): StEnq, myseq 32, yourseen 30, DTE up
Serial3(in): Status, myseq 32
This sample includes output from many interfaces. The boldface type is used to
highlight interface serial 0. Here is the definition of what you see:
StEnq This is an LMI status enquiry sent from the router to the Frame
Relay switch.
Status This is the reply sent to the router from the Frame Relay switch.
mysec This is the local keepalive number. The value is the sequence
identifier.
yourseen This is the keepalive sent by the other side of the serial connection.
DTE This is the data-termination equipment status. In this example, it is up.
The in and out specify the directions that the packets are sent. The out-
bound packets are keepalives sent by the local side, whereas the inbound
packets are the keepalives sent from the other end.
If the sequence numbers for a given interface don't increment, then there
is probably a timing or line problem at one end or the other of the connec-
tion. The line will reset if two out of six consecutive keepalive packets fail
to increment. Although the Layer 3 protocol considers the line protocol to be
down, the Layer 2 protocol continues to send keepalive messages. Once
the Layer 2 protocol achieves three consecutive sequences, the line protocol
is brought back up.
Here is a sample of HDLC communication:
Router_A#debug serial interface
Serial network interface debugging is on
Serial0: HDLC myseq 172188, mineseen 172188*, yourseen
172326, line up
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