Serial Interface ignore Command

johnlloyd_13 · ‎01-20-2016

hi all,

i would like to know if 2911 (or any of its IOS) supports the serial interface command ignore cts.

the 3925 has it but not the 2911. was wondering if it's a platform or IOS limitation.

could someone please advise if this is supported on 2911?

3925#sh ve
Cisco IOS Software, C3900 Software (C3900-UNIVERSALK9-M), Version 15.4(1)T1, RELEASE SOFTWARE (fc2)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2014 by Cisco Systems, Inc.
Compiled Wed 12-Feb-14 06:33 by prod_rel_team

ROM: System Bootstrap, Version 15.0(1r)M16, RELEASE SOFTWARE (fc1)

3925 uptime is 41 weeks, 1 day, 20 hours, 22 minutes
System returned to ROM by power-on
System restarted at 06:13:48 UTC Tue Apr 7 2015
System image file is "flash0:c3900-universalk9-mz.SPA.154-1.T1.bin"
Last reload type: Normal Reload
Last reload reason: power-on

3925(config)#int s0/0/0
3925(config-if)#ignore ?
cts DTE ignore cts
dcd DTE ignore dcd
dsr DTE ignore dsr

3925(config-if)#ignore

2911#sh ve
Cisco IOS Software, C2900 Software (C2900-UNIVERSALK9-M), Version 15.4(3)M2, RELEASE SOFTWARE (fc2)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2015 by Cisco Systems, Inc.
Compiled Fri 06-Feb-15 17:29 by prod_rel_team

ROM: System Bootstrap, Version 15.0(1r)M15, RELEASE SOFTWARE (fc1)

2911 uptime is 1 hour, 10 minutes
System returned to ROM by power-on
System image file is "flash0:c2900-universalk9-mz.SPA.154-3.M2.bin"
Last reload type: Normal Reload
Last reload reason: power-on

2911(config)#int s0/2/0
2911(config-if)#ignore ?
dcd ignore dcd

Mark Malone · ‎01-21-2016

Hey

you can check what your ios version/platform supports exactly on this link

http://tools.cisco.com/ITDIT/CFN/jsp/index.jsp

Peter Paluch · ‎01-21-2016

John, Mark,

Please allow me to join.

The Feature Navigator Tool referenced by Mark is, sadly, not very reliable. I am using it every now and then but I consider the results provided by this tool to be rather approximate and not definitive. It seems that the information about IOSes is not always entirely complete, or sometimes, the same feature is recorded under different names. In addition, I am not quite sure what feature (and its name) would be related to this ignore command.

I was able to dig out a command reference for this command here, and it seems that since 12.3(2)T, the command should be supported:

http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/interface/command/ir-cr-book/ir-i1.html#wp4965157900

However, the set of allowable signals to ignore differs depending on the cable type (DCE or DTE, perhaps even on the serial interface subtype - V.35, X.21, RS-232, RS-449, ...) and on the synchronous or asynchronous mode of operation - see the link above.

John, my question is: Are the serial interface modules in your 3925 and 2911 of the very same type? Is the cable itself of the very same type (DCE/DTE, physical standard used)? The show inventory and show controllers serial ... from both routers would be helpful.

Best regards,
Peter

johnlloyd_13 · ‎01-21-2016

hi peter,

how are you? happy new year and glad to hear from you again!

i agree that the FN is not reliable tool these days. i made a search that the ignore cts command was supported on the 2600 routers. we're having strange issue (for some sites) that VSAT WAN doesn't work well and first thing i see is CTS status is down. i'm not sure if it's a modem, WIC or serial cable issue. after i replace with another smart serial cable, VSAT works smoothly: no CRC and packet drops.

the WIC cards and serial cables are different. these are connected to VSAT modems: 3925 on landing/onshore site and 2911 on remote site.

3925#sh controller serial0/3/1
Interface Serial0/3/1
Hardware is HWIC-Serial
DTE 530

Lead Modem Status
     DCD=up DSR=up DTR=up RTS=up CTS=up

Lead Line Status
     DCD=up DSR=up DTR=up RTS=down CTS=down

Clock Freq detected Rx clk/Tx clk 1025659/1025659 (+-10%)
idb at 0x4059882C, driver data structure at 0x40599618
Stats for LED(s):
Loopback bitmask 0x0
LED1 is Green

2911#sh controller serial0/0/0
Interface Serial0/0/0
Hardware is SCC
DTE V.35
Clock Freq detected Rx clk/Tx clk 1025667/1025667 (+-10%)

NAME: "WAN Interface Card - HWIC Serial 1T on Slot 0 SubSlot 0", DESCR: "WAN Interface Card - HWIC Serial 1T"
PID: HWIC-1T           , VID: V05 , SN: FOC18453E51

issue captured before on serial interface:

#sh int 0/0/0
Serial0/0/0 is up, line protocol is up
Hardware is HWIC-Serial
MTU 1500 bytes, BW 1024 Kbit/sec, DLY 20000 usec,
     reliability 255/255, txload 1/255, rxload 1/255
Encapsulation FRAME-RELAY, loopback not set
Keepalive not set
Restart-Delay is 0 secs
CRC checking enabled
LMI DLCI 1023 LMI type is CISCO frame relay DTE
FR SVC disabled, LAPF state down
Broadcast queue 0/64, broadcasts sent/dropped 59/0, interface broadcasts 0
Last input never, output 00:20:25, output hang never
Last clearing of "show interface" counters 00:59:03
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 412
Queueing strategy: fifo
Output queue: 40/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
     0 packets input, 0 bytes, 0 no buffer
     Received 0 broadcasts (0 IP multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     259 packets output, 35733 bytes, 0 underruns
     0 output errors, 0 collisions, 5 interface resets
     0 unknown protocol drops
     0 output buffer failures, 0 output buffers swapped out
     4 carrier transitions
     DCD=up DSR=up DTR=up RTS=up CTS=down

Peter Paluch · ‎01-23-2016

Hi John,

All the very best to you as well! It's so nice to be in touch with you again.

Unfortunately, with this issue, I am at a loss. Obviously, it is up to the IOS and the WIC card combination whether the ignore cts is supported. On the other hand, CTS is a part of the hardware flow control mechanism between the VSAT/modem and your serial interface, and ignoring it may suppress a symptom but not solve the underlying issue. If I understood you correctly, your issue could be solved by swapping the serial cable, right? If that is true then I believe that it was the only correct way of solving this problem.

Best regards,
Peter

johnlloyd_13 · ‎01-23-2016

hi peter,

yes, swapping the serial cable solved our issue but didn't resolve why CTS was down in the first place. i might lab or ask TAC about this. thanks for your update and hope to see you around in CSC.

Peter Paluch · ‎01-24-2016

Hi John,

swapping the serial cable solved our issue but didn't resolve why CTS was down in the first place

I may be missing something but the simplest explanation is often the correct one (Occam's razor rule). If changing the cable helped restore the proper CTS state, is it possible that the cable itself could have been faulty.

I am most probably saying only what you know already, but the CTS signal is asserted by the DCE device (modem or the VSAT box) whenever it is prepared to handle received data from the attached DTE (in this case, your router). There are only three basic possibilities why the DCE was not indicated as up on your router:

It was not asserted by the modem/VSAT
It was not properly carried in the cable you have used
It was not properly read and understood by your router's serial interface

Now, because changing the cable solved the issue, options 1 and 3 are refuted, and what remains is the option 2.

Do you think something else was at work?

Best regards,
Peter