Connected and disconnected at the same time

[ghost]

Issue and Steps to Reproduce

I currently run 2 c-lightning nodes called Bitkoins.nl and Myshtery and they share a channel. I noticed that Myshtery sometimes disconnects from my other node for no reason. Both are running without problems. Just now I get on Myshtery:
"peers": [ { "id": "02888244029c5909593038ab19f269947c720de3423e491791b46c7c92f76279b6", "connected": true,
while on Bitkoins.nl:
"id": "026bc066924bca8a22e4baa751533bf2dda4161544d08dab544a001a5385ab0d0c", "connected": false,

I still think all this trouble started after version 7.2. With version 7.2 I never had any of these problems like #3194 for example.

ALSO: on Bitkoins.nl how can getinfo say
"num_inactive_channels": 0,

while listpeers gives:
{ "id": "026bc066924bca8a22e4baa751533bf2dda4161544d08dab544a001a5385ab0d0c", "connected": false, "channels": [ { "state": "CHANNELD_NORMAL", "scratch_txid": "59d75dfbca3577afb6ff30f4cb53309804725dddb049270229e1aedf6032e6d8", "short_channel_id": "599602x1804x0", "direction": 1, "channel_id": "468bc68dd776b1720c547594c88c76e2912453e04cde620f10d9e5a2db6dae59", "funding_txid": "59ae6ddba2e5d9100f62de4ce0532491e2768cc89475540c72b176d78dc68b46", "private": false, "funding_allocation_msat": { "02888244029c5909593038ab19f269947c720de3423e491791b46c7c92f76279b6": 0, "026bc066924bca8a22e4baa751533bf2dda4161544d08dab544a001a5385ab0d0c": 804742000 }, "funding_msat": { "02888244029c5909593038ab19f269947c720de3423e491791b46c7c92f76279b6": "0msat", "026bc066924bca8a22e4baa751533bf2dda4161544d08dab544a001a5385ab0d0c": "804742000msat" }, "msatoshi_to_us": 417796011, "to_us_msat": "417796011msat", "msatoshi_to_us_min": 0, "min_to_us_msat": "0msat", "msatoshi_to_us_max": 422671011, "max_to_us_msat": "422671011msat", "msatoshi_total": 804742000, "total_msat": "804742000msat", "dust_limit_satoshis": 546, "dust_limit_msat": "546000msat", "max_htlc_value_in_flight_msat": 18446744073709551615, "max_total_htlc_in_msat": "18446744073709551615msat", "their_channel_reserve_satoshis": 8047, "their_reserve_msat": "8047000msat", "our_channel_reserve_satoshis": 8047, "our_reserve_msat": "8047000msat", "spendable_msatoshi": 409749011, "spendable_msat": "409749011msat", "htlc_minimum_msat": 0, "minimum_htlc_in_msat": "0msat", "their_to_self_delay": 144, "our_to_self_delay": 144, "max_accepted_htlcs": 30, "status": [ "CHANNELD_NORMAL:Reconnected, and reestablished." ], "in_payments_offered": 41, "in_msatoshi_offered": 673394733, "in_offered_msat": "673394733msat", "in_payments_fulfilled": 40, "in_msatoshi_fulfilled": 618396011, "in_fulfilled_msat": "618396011msat", "out_payments_offered": 27, "out_msatoshi_offered": 350795553, "out_offered_msat": "350795553msat", "out_payments_fulfilled": 19, "out_msatoshi_fulfilled": 200600000, "out_fulfilled_msat": "200600000msat", "htlcs": [] } ]

But maybe inactive and disconnected mean different things.

After a restart of Myshtery everything turned normal again with both sides giving connected but of course that's not the solution to the problem.

getinfo output

Both are running the same latest software:
Myshtery:
{ "id": "026bc066924bca8a22e4baa751533bf2dda4161544d08dab544a001a5385ab0d0c", "alias": "myshtery", "color": "23375f", "num_peers": 1, "num_pending_channels": 0, "num_active_channels": 1, "num_inactive_channels": 0, "address": [], "binding": [ { "type": "ipv4", "address": "192.168.178.20", "port": 9835 } ], "version": "v0.7.3-31-ga70f2dc", "blockheight": 603122, "network": "bitcoin", "msatoshi_fees_collected": 0, "fees_collected_msat": "0msat", "lightning-dir": "/home/user/.lightning_test" }

Bitkoins.nl:
{ "id": "02888244029c5909593038ab19f269947c720de3423e491791b46c7c92f76279b6", "alias": "Bitkoins.nl", "color": "23354d", "num_peers": 13, "num_pending_channels": 0, "num_active_channels": 11, "num_inactive_channels": 0, "address": [ { "type": "ipv4", "address": "82.217.214.215", "port": 9735 }, { "type": "torv2", "address": "tjeuwxa2rr24iprs.onion", "port": 9735 }, { "type": "torv3", "address": "2bh7psr4dinasuz3d6jm5o56ebkmlnotqqptoesikzvsyqxwmaneyiad.onion", "port": 9735 } ], "binding": [ { "type": "ipv4", "address": "192.168.178.20", "port": 9735 } ], "version": "v0.7.3-31-ga70f2dc", "blockheight": 603117, "network": "bitcoin", "msatoshi_fees_collected": 144441, "fees_collected_msat": "144441msat", "lightning-dir": "/home/user/.lightning" }

[ghost]

Closing this issue as I got the feeling this issue has been solved since #3194 has been solved. Node Estonia was often disconnected and then connected again which seems related to the what was reported here.I don't see that anymore since I updated to version v0.7.3-88-gf075b87. Will reopen if it occurs again.

[ghost]

Reopening this because it's still an issue.

[ghost]

Happened again today:

"id": "02aecde3b3dde450889755d4dbce538e6b9e9dfa7702d14b5bc5c4379e1b330392",
says:
"id": "02888244029c5909593038ab19f269947c720de3423e491791b46c7c92f76279b6",
"connected": true,

"id": "02888244029c5909593038ab19f269947c720de3423e491791b46c7c92f76279b6",
says
"id": "02aecde3b3dde450889755d4dbce538e6b9e9dfa7702d14b5bc5c4379e1b330392",
"connected": false,

Both run: v0.8.0-1-gb14b2b0

[cdecker]

This can happen sometimes if the connection was interrupted and no messages have been sent for a while (TCP timeout). You can try pinging the other side of the channel and see if it responds:

Run the following on 02888244029c5909593038ab19f269947c720de3423e491791b46c7c92f76279b6

lightning-cli ping 02aecde3b3dde450889755d4dbce538e6b9e9dfa7702d14b5bc5c4379e1b330392

and/or this on 02aecde3b3dde450889755d4dbce538e6b9e9dfa7702d14b5bc5c4379e1b330392

lightning-cli ping 02888244029c5909593038ab19f269947c720de3423e491791b46c7c92f76279b6

[ghost]

Thanks again! I will do so the next time it happens again but why don't they disconnect both at around the same time (so after a while)?

[ZmnSCPxj]

Because TCP is actually a hack on top of IP, the connection is provided by the TCP layer and the two TCP layers on the two computers are not necessarily 100% in sync at all times.

See, IP is just a datagram protocol with resilient but NOT reliable sending. So TCP sends out data and then ACKs back. So for example if Alice TCP layer sends out a datagram to Bob TCP layer, Bob starts a timer then (last time it saw Alice datagram). Then Bob sends back an ACK to Alice TCP. When Alice TCP receives it, it starts a timer (last time it saw Bob datagram). Then the Internet breaks between them, but they cannot see this immediately (because IP is a datagram protocol, so most of the time what they will see is nothing because there is no message ongoing, so they cannot detect Internet breakage). Then Bob timer times out faster and it thinks it has disconnected but Alice (whose timer was started later) thinks it is still connected.