PPPoE client receiving unexpected PADT

Teleshed · ‎09-20-2018

This is an issue that I now have to admit defeat on and reach out to the community for help.

I have a 7204VXR with an NPE-G1 and a single PA-2FE-TX module. I am trying to configure this as a PPPoE client, connecting to an Openreach VDSL/Ethernet modem.

This NPE is running 15.2(4)M11:

Cisco IOS Software, 7200 Software (C7200-ADVIPSERVICESK9-M), Version 15.2(4)M11, RELEASE SOFTWARE (fc2)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2016 by Cisco Systems, Inc.
Compiled Sun 16-Oct-16 07:53 by prod_rel_team

The connection comes up as expected and I am able to pass traffic over the PPPoE link okay. However, after approximately 2 minutes the client receives a PADT frame from the remote peer and the connection is brought down. The connection comes back up and then the cycle repeats.

Normally, I would be reaching out to the ISP regarding this issue. In this case, the connection works reliably (and has done for some time) when using a MikroTik router, an ISR 3825 (which is no longer available), even an Apple AirPort. I'm convinced that even though the remote peer is sending the PADT it is some nuance of the client that is causing this to happen.

I've stripped the configuration down to the bare minimum. This is attached in conf.txt.

In the below console log, you can see the interface bouncing up and down. You can also see that traffic (ICMP at least, I have also done TCP) is passing properly.

*Sep 20 05:38:57.079: %SYS-5-CONFIG_I: Configured from console by console
*Sep 20 05:38:57.503: %LINK-3-UPDOWN: Interface Dialer1, changed state to up
*Sep 20 05:39:11.711: %DIALER-6-BIND: Interface Vi2 bound to profile Di1
*Sep 20 05:39:11.715: %LINK-3-UPDOWN: Interface Virtual-Access2, changed state to up
*Sep 20 05:39:12.051: %LINEPROTO-5-UPDOWN: Line protocol on Interface Virtual-Access2, changed state to up
Router#ping 8.8.8.8
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 8.8.8.8, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 16/16/16 ms
Router#
*Sep 20 05:41:36.919: %DIALER-6-UNBIND: Interface Vi2 unbound from profile Di1
*Sep 20 05:41:36.923: %LINEPROTO-5-UPDOWN: Line protocol on Interface Virtual-Access2, changed state to down
*Sep 20 05:41:36.923: %LINK-3-UPDOWN: Interface Virtual-Access2, changed state to down
*Sep 20 05:41:59.039: %DIALER-6-BIND: Interface Vi2 bound to profile Di1
*Sep 20 05:41:59.043: %LINK-3-UPDOWN: Interface Virtual-Access2, changed state to up
*Sep 20 05:41:59.311: %LINEPROTO-5-UPDOWN: Line protocol on Interface Virtual-Access2, changed state to up
*Sep 20 05:44:28.643: %DIALER-6-UNBIND: Interface Vi2 unbound from profile Di1
*Sep 20 05:44:28.647: %LINEPROTO-5-UPDOWN: Line protocol on Interface Virtual-Access2, changed state to down
*Sep 20 05:44:28.647: %LINK-3-UPDOWN: Interface Virtual-Access2, changed state to down
*Sep 20 05:44:50.823: %DIALER-6-BIND: Interface Vi2 bound to profile Di1
*Sep 20 05:44:50.827: %LINK-3-UPDOWN: Interface Virtual-Access2, changed state to up
*Sep 20 05:44:51.131: %LINEPROTO-5-UPDOWN: Line protocol on Interface Virtual-Access2, changed state to up
*Sep 20 05:47:10.803: %DIALER-6-UNBIND: Interface Vi2 unbound from profile Di1
*Sep 20 05:47:10.807: %LINEPROTO-5-UPDOWN: Line protocol on Interface Virtual-Access2, changed state to down
*Sep 20 05:47:10.807: %LINK-3-UPDOWN: Interface Virtual-Access2, changed state to down
*Sep 20 05:47:33.039: %DIALER-6-BIND: Interface Vi2 bound to profile Di1
*Sep 20 05:47:33.043: %LINK-3-UPDOWN: Interface Virtual-Access2, changed state to up
*Sep 20 05:47:33.359: %LINEPROTO-5-UPDOWN: Line protocol on Interface Virtual-Access2, changed state to up

Also, for completeness, here is the output of debug pppoe packets showing the PADT:

*Sep 20 10:53:01.723: PPPoE 1558: I PADT  R:a0f3.e434.6d49 L:0017.9459.8738 Fa2/0
contiguous pak, size 60
         00 17 94 59 87 38 A0 F3 E4 34 6D 49 88 63 11 A7
         06 16 00 00 00 00 00 00 00 00 00 00 00 00 00 00
         00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
         00 00 00 00 00 00 00 00 10 51 92 B9
*Sep 20 10:53:01.723: [0]PPPoE 1558: O PADT  R:a0f3.e434.6d49 L:0017.9459.8738 Fa2/0
contiguous pak, size 60
         A0 F3 E4 34 6D 49 00 17 94 59 87 38 88 63 11 A7
         06 16 00 00 00 00 00 00 00 00 00 00 00 00 00 00
         00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
         00 00 00 00 00 00 00 00 00 00 00 00
*Sep 20 10:53:01.723: %DIALER-6-UNBIND: Interface Vi2 unbound from profile Di1
*Sep 20 10:53:01.727: %LINEPROTO-5-UPDOWN: Line protocol on Interface Virtual-Access2, changed state to down
*Sep 20 10:53:01.727: %LINK-3-UPDOWN: Interface Virtual-Access2, changed state to down

I've have spent many many hours trying to resolve this. I have adjusted many settings; timeouts, connection parameters, slightly older IOS version etc. All to no avail. However, I'm back to basics on this and am throwing my arms up in despair.

Georg Pauwen · ‎09-20-2018

Hello,

the first thing I would do is get into the Openreach and check if you are are running the latest (available) firmware...

Teleshed · ‎09-20-2018

An interesting thought, and certainly something that I'll look into. However:

I have another VDSL line from a different provider that exhibits the exact same issues.

Since the modem is simply bridging, my assumption was that the PPPoE traffic was coming from the AC rather than the Openreach modem.

I will look into the firmware and report back. Thanks for your suggestion.

Teleshed · ‎09-22-2018

Okay, the Openreach modem has been checked to be running the latest firmware.

I have also been able to borrow a DrayTek Vigor 130.

I am still seeing the same issues. :(

My 3825 recently died (which is why I'm setting up this 7204VXR) but I think I have a couple of old 2811s somewhere. I'm going to see if the issue is present on one of those too.

Georg Pauwen · ‎09-22-2018

Hello,

it either comes from the modem or from the ISP. Check if your ISP has some sort of volume limiting enabled, or if at least they can check on their end...