[cisco-nas] X.75 (LAPB-TA) sessions getting "stuck"? (AS5300, 12.3)

[Aaron Leonard]

Hi Gert,

> I have this AS5300 that is handling incoming X.75/LAPB-TA calls, and
> every few weeks, it seems to get stuck in weird ways.

Well, since I was the one who talked you into using the 5300 for
this, I suppose I bear some responsibility here.

> Incoming calls connect fine, and the initial few bytes ("username, password")
> are exchanged fine.  After that, nothing sent by the AS5300 to the ISDN
> side arrives at the caller location - but "debug lapb-ta packets" *does*
> log the packets just fine...:
> 
> Oct  2 12:56:01: %LINK-3-UPDOWN: Interface Serial0:0, changed state to up
> Oct  2 12:56:01: %ISDN-6-CONNECT: Interface Serial0:0 is now connected to 8912003682 N/A
> Oct  2 12:56:04: LAPB-TA: Autodetect trying to detect LAPB on Se0:0
> Oct  2 12:56:04:   sampled pkt:  2 bytes:  1 3F.. match
> Oct  2 12:56:04: LAPBTA: get_ll_config: Serial0:0
> Oct  2 12:56:04: LAPBTA127: vty allocated for Se0:0
> Oct  2 12:56:04: LAPBTA127: process 81
> Oct  2 12:56:04: Se0:0: LAPB-TA started
> Oct  2 12:56:04: LAPBTA: service change: LAPB physical layer up, context 62CC3A58 interface up, protocol down
> Oct  2 12:56:04: LAPBTA: service change: , context 62CC3A58 up
> Oct  2 12:56:04: LAPB-TA: Se0:0, 14 sent
> Oct  2 12:56:04: LAPB-TA: Se0:0, 1 rcvd
> Oct  2 12:56:04: LAPB-TA: Se0:0, 3 rcvd
> Oct  2 12:56:04: LAPB-TA: Se0:0, 4 rcvd
> Oct  2 12:56:04: LAPB-TA: Se0:0, 3 sent
> Oct  2 12:56:04: LAPB-TA: Se0:0, 5 rcvd
> Oct  2 12:56:04: LAPB-TA: Se0:0, 5 sent
> Oct  2 12:56:04: LAPB-TA: Se0:0, 2 rcvd
> Oct  2 12:56:04: LAPB-TA: Se0:0, 6 sent
> Oct  2 12:56:04: LAPB-TA: Se0:0, 10 sent
> Oct  2 12:56:05: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0:0, changed state to up
> Oct  2 12:56:07: LAPB-TA: Se0:0, 5 sent
> Oct  2 12:56:07: LAPB-TA: Se0:0, 21 sent
> 
> - about here, it breaks.  Nothing ever arrives at the calling side anymore
> (and nothing the other side shows up as "rcvd" either).
> 
> Oct  2 12:56:07: LAPB-TA: Se0:0, 4 sent
> Oct  2 12:56:17: LAPB-TA: Se0:0, 21 sent
> Oct  2 12:56:17: LAPB-TA: Se0:0, 4 sent
> Oct  2 12:56:27: LAPB-TA: Se0:0, 21 sent
> Oct  2 12:56:27: LAPB-TA: Se0:0, 4 sent
> Oct  2 12:56:37: LAPB-TA: Se0:0, 21 sent
> Oct  2 12:56:37: LAPB-TA: Se0:0, 4 sent
> Oct  2 12:57:11: LAPBTA127: stopped, removing lapb
> Oct  2 12:57:11: LAPBTA: service change: LAPB deleted, context 62CC3A58 interface up, protocol down, disconnecting
> Oct  2 12:57:11: LAPBTA: removing context 62CC3A58
> Oct  2 12:57:11: %ISDN-6-DISCONNECT: Interface Serial0:0  disconnected from 8912003682 , call lasted 70 seconds
> Oct  2 12:57:11: LAPBTA: close 62DDA294, line 127
> Oct  2 12:57:11: %LINK-3-UPDOWN: Interface Serial0:0, changed state to down
> 
> ... nothing unusual in the log, it just seems as if "LAPB-TA" loses contact
> to "the ISDN side of things".  No real idea how to debug this further...

My generic approach would be something like this:

Compare and contrast what happens when things are working as desired,
what what is happening when things are not.

Things to compare:

- debugs:
  debug isdn q931
  debug lapb-ta data
  debug lapb-ta error
  debug lapb-ta event
  debug modem

- during that little 1-minute window where things are stuck, get:

  show line vty <n>    <= on the VTY used by the LAPB-TA session
  show interface serial0:<n>  <= on the B channel used by the call

  compare how the vty and the serial interface look, with how they
  look when things are working right

> If I reboot the box, everything is back to working.  "shut / no shut" on
> the serial0:15 interface did *not* change anything.

I'm guessing that you've got some problem with a vty, but that's just
a guess.  If so, then maybe you could do a "clear line" on the vty
to get things unstuck.

> This is currently running 12.3(26), which is the latest 12.3 release.
> 
> 
> I'd bet willing to try an upgrade to 12.4, but this brings up the next
> question - is the 5300 supported in 12.4?

Nope.  12.3 mainline is the last branch to support the 5300.

> The IOS files that can be
> found on the FTP server in 12.4/12.4.25b/as5300/ are all named "as5350-...",
> so I'm wondering whether they will work on the 5300 as well, or whether
> this is incompatible, and the directory naming is just weird.

The 5350 is an entirely different system from the 5300, and neither's
images will boot on the other.

> (We could also downgrade to 12.2, if this is a new problem in 12.3...)
> 
> gert

Yeah, if you just want to try different code versions, you could try
(among stuff that's still on CCO):

12.3(3i)
12.2(15)T7

Good luck,

Aaron