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CISCO887VAG+7-K9 router - 3G doesn't kick in when PPP drops but sync remains

We use Cisco 800 series routers in our branches to establish IPSEC VPN connectivity with our headend ASA firewalls.

At some key sites, we have deployed CISCO887VAG+7-K9 routers with the intention that the 3G cellular interface will kick in if connectivity via ADSL drops. To achieve this, the cellular interface is configured as a backup interface and we are tracking line protocol on the ATM interface. This seems to work well for instances where there is a clear drop of the ADSL interface e.g. if you disconnect the ADSL cable, then the 3G will kick in and connectivity will resume. When the ADSL cable is reconnected, connectivity is restored via ADSL)

However, we have come across an issue where connectivity drops via ADSL but 3G does not kick in. It seems that on such occasions, PPP is lost but the sync is still present (I believe the ADSL CD light on router remains solid though I can’t confirm this 100% as I’m not actually based at the site experiencing the issue) In these cases, since the ATM interface is still “up” I believe that is why it doesn’t fail over to the cellular interface. However, we are still stuck without connectivity due to the loss of PPP. E.g. from the router logs:

Mar 12 18:20:36.447: %LINK-3-UPDOWN: Interface Virtual-Access1, changed state to down

---Connectivity lost here----

Mar 12 19:08:43.427: %LINK-3-UPDOWN: Interface ATM0, changed state to down

Mar 12 19:09:03.426: %LINK-3-UPDOWN: Interface ATM0, changed state to up

---Connectivity resumes via ADSL but no connectivity from 18:20hrs to 19:09hrs (3G didn’t kick in)---

Mar 12 19:09:18.509: %LINK-3-UPDOWN: Interface Virtual-Access1, changed state to up

---Connectivity lost here----

Mar 13 02:59:34.329: %LINK-3-UPDOWN: Interface Virtual-Access1, changed state to down

Mar 13 08:41:36.010: %LINK-3-UPDOWN: Interface ATM0, changed state to down

Mar 13 08:41:56.052: %LINK-3-UPDOWN: Interface ATM0, changed state to up

---Connectivity resumes via ADSL but no connectivity from 02:59hrs to 08:42hrs (3G didn’t kick in)---

Mar 13 08:42:22.971: %LINK-3-UPDOWN: Interface Virtual-Access1, changed state to up

My interpretation of the above is that, for some reason, the PPP session drops at 18:20hrs (at this point, we lose connectivity) signified by the Virtual-Access1 changing state to DOWN. However, the ATM0 interface itself remains UP until 19:08hrs when it drops momentarily and then re-establishes PPP (Virtual-Access1 changes state to UP) and our connectivity resumes again over ADSL at this point. PPP then drops again at 02:59hrs (we lose connectivity as a result) and, again, the ATM0 interface remains up until 08:41 when it momentarily flaps, then PPP is re-established and connectivity resumes via ADSL at 08:42hrs.

So I guess my first question is – does my interpretation of what is happening seem correct?

If so, then:

  • 1) What would cause PPP to drop but not the ATM0 interface itself? Is there anything I can do to imrpove/rectify this situation? It seems to be a similar issue to that experienced by some users with the Cisco887VA router (i.e. without 3G backup) as detailed here:

https://supportforums.cisco.com/message/3689942#3689942

  • 2) In the above situation, where PPP drops but not the ATM0 interface, is there any way I can get the 3G to take over to prevent loss of connectivity for such extended periods?

Below is the output from show controller vdsl 0:

Controller VDSL 0 is UP

Daemon Status: Up

XTU-R (DS) XTU-C (US)

Chip Vendor ID: 'BDCM' 'IFTN'

Chip Vendor Specific: 0x0000 0x71BE

Chip Vendor Country: 0xB500 0xB500

Modem Vendor ID: 'CSCO' ' '

Modem Vendor Specific: 0x4602 0x0000

Modem Vendor Country: 0xB500 0x0000

Serial Number Near: FTX154785AB C887VAG+ 15.1(4)M

Serial Number Far:

Modem Version Near: 15.1(4)M

Modem Version Far: 0x71be

Modem Status: TC Sync (Showtime!)

DSL Config Mode: AUTO

Trained Mode: G.992.1 (ADSL) Annex A

TC Mode: ATM

Selftest Result: 0x00

DELT configuration: disabled

DELT state: not running

Trellis: ON ON

Line Attenuation: 44.0 dB 26.5 dB

Signal Attenuation: 44.0 dB 0.0 dB

Noise Margin: 11.7 dB 12.0 dB

Attainable Rate: 7192 kbits/s 1000 kbits/s

Actual Power: 20.1 dBm 11.9 dBm

Total FECS: 14269 0

Total ES: 51 0

Total SES: 0 0

Total LOSS: 0 0

Total UAS: 0 0

Total LPRS: 0 0

Total LOFS: 0 0

Total LOLS: 0 0

Bit swap: 0 0

Full inits: 3

Failed full inits: 0

Short inits: 0

Failed short inits: 0

Firmware Source File Name (version)

-------- ------ -------------------

VDSL embedded VDSL_LINUX_DEV_01212008 (1)

Modem FW Version: 110506_1916-4.02L.03.A2pv6C032b.d23i

Modem PHY Version: A2pv6C032b.d23i

DS Channel1 DS Channel0 US Channel1 US Channel0

Speed (kbps): 0 4800 0 800

Previous Speed: 0 8000 0 928

Total Cells: 0 165585725 0 0

User Cells: 0 78294 0 0

Reed-Solomon EC: 0 14269 0 5

CRC Errors: 0 65 0 0

Header Errors: 0 136 0 0

Interleave (ms): 0.00 8.00 0.00 8.00

Actual INP: 0.00 0.80 0.00 1.14

Training Log : Stopped

Training Log Filename : flash:vdsllog.bin

Any advice/thoughts on this issue would be appreciated!