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Author Topic: recommended settings for ppp lcp echo interval?  (Read 2747 times)


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recommended settings for ppp lcp echo interval?
« on: August 14, 2017, 12:23:49 PM »

My PlusNet ADSL connection has been rock solid for years. Last week, my connection started dropping randomly, sometimes several times a day and sometimes overnight. Network load wasn't a factor. Phone line tests showed no issues. PlusNet said they thought the problem was in my network. And sure enough, my router debug logs showed my router was terminating the PPP connection because the PPP peer had stopped replying to the router's LCP Echo requests. My router was therefore taking the connection down.

Suspecting a hardware issue, I swapped the modem out for a spare but the problem remained. On a hunch, I tried doubling the LCP Echo interval setting in the router. The link has now been up for several days with no drops whatsoever. Maybe a config change in the ISP network caused this change to be needed or maybe my LCP settings were too aggressive and it's just luck I've had no problems until now. I've no idea.

But this got me wondering. What are the recommended PPP LCP Echo settings for DSL connections. Any thoughts?

The PPP LCP defaults in the my router are:-
lcp-echo-interval 5
lcp-max-failure 6

The lcp-echo-adaptive setting means the router will only send new LCP Echo requests if no data is received from the peer since the last LCP Echo was sent. Thus my router sends LCP Echo requests more often when the connection is idle.

I doubled lcp-echo-interval to 10 and the connection is now stable.  :)

My setup is an unlocked HG612, ADSL2, connected directly to a Ubiquiti Edgerouter-Lite which does PPPoE.


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Re: recommended settings for ppp lcp echo interval?
« Reply #1 on: August 14, 2017, 09:57:40 PM »

An interesting question.

Not having any idea how my G.992.3 connection is configured, I took a look at a previously saved Wireshark session. I see that each end issues an LCP Echo Request approximately every 30 seconds.

The "A" end --

      9 1.034920664    Dell_c1:20:9e     PPP LCP  32     Echo Request
    470 31.035905448   Dell_c1:20:9e     PPP LCP  32     Echo Request
    518 61.060214635   Dell_c1:20:9e     PPP LCP  32     Echo Request
    622 91.066676019   Dell_c1:20:9e     PPP LCP  32     Echo Request
    722 121.071766896  Dell_c1:20:9e     PPP LCP  32     Echo Request
    774 151.095087700  Dell_c1:20:9e     PPP LCP  32     Echo Request
    810 181.119396488  Dell_c1:20:9e     PPP LCP  32     Echo Request

The "B" end --

    366 7.705908487    JuniperN_ea:28:52     PPP LCP  66     Echo Request
    472 36.881021477   JuniperN_ea:28:52     PPP LCP  66     Echo Request
    540 66.882306927   JuniperN_ea:28:52     PPP LCP  66     Echo Request
    628 96.881439171   JuniperN_ea:28:52     PPP LCP  66     Echo Request
    724 126.882682316  JuniperN_ea:28:52     PPP LCP  66     Echo Request
    776 156.882011863  JuniperN_ea:28:52     PPP LCP  66     Echo Request
    812 186.883479411  JuniperN_ea:28:52     PPP LCP  66     Echo Request
:cat:  100% Linux and, previously, Unix. Co-founder of the ELRepo Project.

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