diff options
Diffstat (limited to 'node')
| -rw-r--r-- | node/Packet.hpp | 24 |
1 files changed, 18 insertions, 6 deletions
diff --git a/node/Packet.hpp b/node/Packet.hpp index 0c07fa24..e1d38de5 100644 --- a/node/Packet.hpp +++ b/node/Packet.hpp @@ -664,20 +664,32 @@ public: /** * ECHO request (a.k.a. ping): - * <[...] arbitrary payload to be echoed back> + * <[1] 8-bit purpose of echo request> + * <[...] additional arbitrary payload> * * This generates OK with a copy of the transmitted payload. No ERROR * is generated. Response to ECHO requests is optional and ECHO may be * ignored if a node detects a possible flood. * - * There is a de-facto standard for ECHO payload. No payload indicates an - * ECHO used for path confirmation. Otherwise the first byte contains - * flags, in which currently the only flag is 0x01 for a user-requested - * echo. For user-requested echoes the result may be reported back through - * the API. Otherwise the payload is for internal use. + * An empty payload is permitted. This is used in some versions for + * path checking and validation. If a payload is present it must + * follow the above format, though the recipient does not have to check + * this. It can simply echo it back. + * + * Echo purpose codes: + * 0x00 - User ECHO request + * 0x01 - Dead path detection * * Support for fragmented echo packets is optional and their use is not * recommended. + * + * Dead path detection is performed by sending ECHOs with the same random + * payload to the best (or every) direct path and then once indirectly + * (such as via a root server). When an OK is received echoing back this + * test payload, all paths that have not yet received this OK are cancelled + * or re-tested. This can be done after a short period of inactivity to + * detect and automatically cancel dead paths without requiring any + * special logic (other than support for ECHO) at the remote end. */ VERB_ECHO = 8, |