Configuration settings

Exceptional settings

• server

  Specifies <servername>. Is looked up in [SERVER] and [COMMON] only. If not specified there, it is SERVER.

  Used by server to select the appropriate parts of the rest of the configuration. Ignored by the client.

• secret

  Looked up in the usual way, but used by client and server to determine which possible peerings to try to set up, and which to ignore.

  We define the sets of putative clients and servers, as follows: all those, for which there is any section (even an empty one) whose name is based on <client> or <servername> (as applicable). (LIMIT sections do not count.)

  The server queue packets for, and accept requests from, each putative client for which the config search yields a secret.

  Each client will create a local interface, and try to communicate with the server, for each possible pair (putative server, putative client) for which the config search yields a secret.

  The value is a string, fed directly into HMAC.

• ipif

  Command to run to create and communicate with local network interface. Passed to sh -c. Must speak SLIP on stdin/stdout.

  (For compatibility with older hippotat, %(var)s is supported too but this is deprecated since the extra s is confusing.)

  On server: applies to all clients; not looked up in client-specific sections. On client: may be different for different servers.

  [string; userv root ipif %{local},%{peer},%{mtu},slip '%{rnets}']

ipif interpolations:

The following interpolations aare substituted in the value for ipif:

Input	%{local}	%{peer}	%{rnets}	%{ifname}
on server	vaddr	vrelay	vnetwork	ifname_server
on client	client	vaddr	vroutes	ifname_client

Always: %{mtu}, and %% to indicate a literal %.

Capped settings

Values in [<server> LIMIT] and [LIMIT] are a cap (maximum) on those from the other sections (including COMMON). If a larger value is obtained, it is (silently) reduced to the limit value.

• max_batch_down

  Size limit for response payloads.

  On client, incoming response bodies are limited to this (plus a fixed constant metadata overhead). Server uses minimum of client’s and server’s configured values (old servers just use server’s value).

  [65536 (bytes); LIMIT: 262144]

• max_batch_up

  Size limit for request upbound payloads. On client, used directly, with LIMIT applied.

  On server, only LIMIT is relevant, and must be at least the client’s configured value (checked).

  [4000 (bytes); LIMIT: 262144]

• max_queue_time

  Discard packets after they have been queued this long waiting for http.

  On server: setting applies to downward packets. On client: setting applies to upward packets.

  [10 (s); LIMIT: 121]

• http_timeout

  On server: return with empty payload any http request oustanding for this long.

  On client: give up on any http request outstanding for for this long plus http_timeout_grace.

  Warning messages about link problems, printed by the client, are rate limited to no more than one per effective timeout.

  Client’s effective timeout must be at least server’s (checked).

  [30 (s); LIMIT: 121]

• target_requests_outstanding

  On client: try to keep this many requests outstanding, to allow for downbound data transfer. On server: whenever number of outstanding requests for a client exceeds this, returns oldest with empty payload. Must match between client and server (checked). [3; LIMIT: 10]

Ordinary settings, used by both, not client-specific

On the server these are forbidden in the client-specific config sections.

• addrs

  Public IP (v4 or v6) address(es) of the server; space-separated. On server: mandatory; used for bind. On client: used only to construct default url. No default.

• vnetwork

  Private network range. Must contain all <client>s. Must contain vaddr and vrelay, and is used to compute their defaults. [CIDR syntax (<prefix>/<length>); 172.24.230.192/28]

• vaddr

  Address of server’s virtual interface. [default: first host entry in vnetwork, so 172.24.230.193]

• vrelay

  Virtual point-to-point address used for tunnel routing (does not appear in packets). [default: first host entry in vnetwork other than vaddr, so 172.24.230.194]

• port

  Public port number of the server. On server: used for bind. On client: used only to construct default url. [80]

  Do not set this to 443 - the server will speak plain unencrypted HTTP on the port you specify, which would be wrong for 443. While the client has integrated TLS support, the server does not. To use hippotat with TLS:

  • Set up a TLS reverse proxy (such as apache or nginx), probably with a certificate from Let’s Encrypt.

  • Configure port and addrs to the internal address and port (to which the reverse proxy forwards the requests).

  • Configure url to the public URL of the reverse proxy.

• mtu

  Of virtual interface. Must match exactly at each end (checked). [1500 (bytes)]

Ordinary settings, used by server only

• max_clock_skew

  Permissible clock skew between client and server. Hippotat will not work if clock skew is more than this. Conversely: when moving client from one public network to another, the first network can deny service to the client for this period after the client leaves the first network. [300 (s)]

• ifname_server

  Virtual interface name on the server. [shippo%d] NB: any %d is interpolated (by the kernel).

Ordinary settings, used by client only

• http_timeout_grace

  See http_timeout. [5 (s)]

• max_requests_outstanding

  Client will hold off sending more requests than this to server even if it has data to send. [6]

• success_report_interval

  If nonzero, report success periodically. Otherwise just report it when we first have success. [3600 (s)]

• http_retry

  If a request fails, wait this long before considering it “finished” - to limit rate of futile requests (and also to limit rate of moaning on stderr). [5 s]

• url

  Public url of server. [http://<first-entry-in-addrs>:<port>/]

• vroutes

  Additional virtual addresses to be found at the server end, space-separated. Routes to those will be created on the client. vrelay is included implicitly. [CIDR syntax, space separated; default: none]

• ifname_client

  Virtual interface name on the client. [hippo%d] NB: any %d is interpolated (by the kernel).