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Make ML_DERP_REGION a Kconfig option instead of a hardcoded #define #29

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Make ML_DERP_REGION a Kconfig option instead of a hardcoded #define #29

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19 changes: 19 additions & 0 deletions components/microlink/Kconfig
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,25 @@ menu "MicroLink V2 Configuration"
communicate with). For large tailnets, set this to the actual
peer count needed, not the total tailnet size.

config ML_DERP_REGION
int "Preferred DERP region ID"
default 9
help
Tailscale DERP region ID to advertise as this node's home region
(sent as Hostinfo.NetInfo.PreferredDERP) and to prefer for STUN
probing/relay fallback before any live latency measurement has
happened. Defaults to 9 (Dallas, Texas) - fine for North America,
but every deployment relying on DERP-relayed traffic (e.g. a peer
behind CGNAT with no direct path) from elsewhere in the world pays
needless latency relaying through Dallas instead of a nearby
region. Real Tailscale clients pick this by STUN-probing several
regions at startup and using whichever has the lowest measured
latency; this project doesn't do that yet, so pick the closest
region to this device's usual network by hand instead. Region IDs
are visible in this device's own boot log (`ml_coord: DERP region
N (code): ...`, printed once the initial MapResponse is parsed) -
e.g. 4 = Frankfurt, 14 = Amsterdam, 18 = Paris.

config ML_PRIORITY_PEER_IP
string "Priority peer VPN IP"
default ""
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10 changes: 8 additions & 2 deletions components/microlink/include/microlink_internal.h
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Expand Up @@ -73,8 +73,14 @@ extern "C" {
#define ML_MAX_PACKET_SIZE 1500
#define ML_DERP_MAX_FRAME (ML_MAX_PACKET_SIZE + 64)

/* DERP */
#define ML_DERP_REGION 9 /* Dallas (dfw) */
/* DERP - preferred region is Kconfig-driven (default 9/Dallas) rather than
* hardcoded, so a deployment relying on DERP-relayed traffic (e.g. a peer
* behind CGNAT with no direct path) elsewhere in the world doesn't pay
* needless latency relaying through Dallas - see ML_DERP_REGION's Kconfig
* help text. ML_DERP_HOST/_PORT stay hardcoded: they're only a bootstrap
* fallback used before the first DERPMap arrives (ml_derp.c's ml_derp_connect
* uses the real per-region host from the parsed DERPMap once available). */
#define ML_DERP_REGION CONFIG_ML_DERP_REGION
#define ML_DERP_HOST "derp9e.tailscale.com"
#define ML_DERP_PORT 443

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