3

This is a lnd.log line:

2019-01-11 12:20:13.904 [DBG] PEER: Sending ChannelUpdate(chain_hash=000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f, short_chan_id=601495532567724033, flag=256, update_time=2019-01-11 12:19:08 +0100 CET) to 46.229.165.136:9735

Since I cannot find a direct correlation with the spec at https://github.com/lightningnetwork/lightning-rfc/blob/master/07-routing-gossip.md can someone clarify the "flag" value?

Where can I find the information below?

[1:message_flags]
[1:channel_flags]
[2:cltv_expiry_delta]
[8:htlc_minimum_msat]
[4:fee_base_msat]
[4:fee_proportional_millionths]
[8:htlc_maximum_msat] (option_channel_htlc_max)

Are they encoded in some way in this "flag"? How?

|improve this question
4

The flags field (2 bytes) has been split into two different (1 byte) fields, the message_flags (most significant bits) and the channel_flags field (least significant bits). Hence the flags value displayed in lnd has the message_flags byte set to 0x00 and the message_flags set to 0x01.

message_flags indicates that this channel_update has some optional fields appended to the end. In this case it has the 0th bit set, which corresponds to the option_channel_htlc_max option, hence the channel_update has an additional field htlc_maximum_msat appended.

|improve this answer
  • So Basically the "Flag" is a 16 bits field [8 bit message_flag + 8 bit channel_flags]. Is it possible to find the others information [cltv_expiry_delta, htlc_minimum_msat, fee_base_msat, fee_proportional_millionths, htlc_maximum_msat] exploring the log or it is only possible by using the lncli getchainifo? How can a Node, receiving a channel update message, understand and set the new channel policies? – Stefano Angieri Jan 15 at 11:31
  • Not too familiar with the lnd RPC interface, I mostly work on c-lightning. But I guess it should list those with peers as well. And you can set all of these parameters on startup using cli options. – cdecker Jan 15 at 12:55

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.