Yu,
The looped state is detected by the HDLC/PPP keepalive mechanism. In PPP,
the LCP magic number should be different between hosts. In HDLC, the
yourseen/myseen values are different for the two ends. If these values are
the same inbound as the ones sent by the interface, the line is declared
"looped". Frame Relay detects a loop the same way HDLC does. ATM can only
detect loops by sending OAM F5 cells, whereby the direction indicator bit
does not change. SMDS cannot detect loops. I am not sure about SDLC and
the IBM variants. X.25 should be the same as Frame Relay.
HTH,
chris
-----Original Message-----
From: Yu Ning [mailto:yuning@ns.chinanet.cn.net]
Sent: Friday, September 29, 2000 12:44 PM
To: cisco-nsp@puck.nether.net
Subject: [nsp] Basic transmission test question (how interface know it's
looped?)
Hi All,
Can anyone tell me why sometimes when we physically loop a circuit, we can
see a
"loop" state from the show interface command. But sometimes when we loop a
line,
we can only see both the interface and line protocol is "up", but not the
word
"loop". In what condition, interface will detect it been looped?
Our current no "loop" hardware is:
SLOT 3 (RP/LC 3 ): 4 port ATM Over SONET OC-3c/STM-1 Multi Mode
MAIN: type 39, 800-4104-01 rev A0 dev 16777215
HW config: 0x01 SW key: FF-FF-FF
PCA: 73-3034-02 rev A0 ver 2
HW version 1.1 S/N CAB0240A9EC
MBUS: MBUS Agent (1) 73-2146-07 rev B0 dev 0
HW version 1.2 S/N CAB0236A4Z8
Test hist: 0xFF RMA#: FF-FF-FF RMA hist: 0xFF
DIAG: Test count: 0xFFFFFFFF Test results: 0xFFFFFFFF
L3 Engine: 0 - OC12 (622 Mbps)
MBUS Agent Software version 01.40 (RAM) (ROM version is 01.33)
Using CAN Bus A
ROM Monitor version 10.00
Fabric Downloader version used 13.01 (ROM version is 13.01)
Primary clock is CSC 1
Board is analyzed
Board State is Line Card Enabled (IOS RUN )
Insertion time: 00:00:11 (8w0d ago)
DRAM size: 268435456 bytes
FrFab SDRAM size: 67108864 bytes
ToFab SDRAM size: 67108864 bytes
0 crashes since restart
We just connect the input with output via fiber.
regards,
------------------------------------------
(Mr.) Yu(2) Ning(2)
Support,Int'l/Domestic Routing
ChinaNET(AS4134) Backbone Operation
Beijing,P.R.C. +86-10-66418105/8121/8122
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