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[dhcp] Extract timing parameters out to config/dhcp.h

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iPXE uses DHCP timeouts loosely based on values recommended by the
specification, but often abbreviated to reduce timeouts for reliable
and/or simple network topologies.  Extract the DHCP timing parameters
to config/dhcp.h and document them.  The resulting default iPXE
behavior is exactly the same, but downstreams are now afforded the
opportunity to implement spec-compliant behavior via config file
overrides.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Modified-by: Michael Brown <mcb30@ipxe.org>
Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Alex Williamson
2015-01-26 10:54:29 -07:00
committed by Michael Brown
parent 5350b65a3c
commit 47aebc24d3
3 changed files with 106 additions and 23 deletions
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87
src/config/dhcp.h Normal file
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#ifndef CONFIG_DHCP_H
#define CONFIG_DHCP_H
/** @file
*
* DHCP configuration
*
*/
FILE_LICENCE ( GPL2_OR_LATER );
#include <config/defaults.h>
/*
* DHCP and PXE Boot Server timeout parameters
*
* Initial and final timeout for DHCP discovery
*
* The PXE spec indicates discover request are sent 4 times, with
* timeouts of 4, 8, 16, 32 seconds. iPXE by default uses 1, 2, 4, 8.
*/
#define DHCP_DISC_START_TIMEOUT_SEC 1
#define DHCP_DISC_END_TIMEOUT_SEC 10
//#define DHCP_DISC_START_TIMEOUT_SEC 4 /* as per PXE spec */
//#define DHCP_DISC_END_TIMEOUT_SEC 32 /* as per PXE spec */
/*
* ProxyDHCP offers are given precedence by continue to wait for them
* after a valid DHCPOFFER is received. We'll wait through this
* timeout for it. The PXE spec indicates waiting through the 4 & 8
* second timeouts, iPXE by default stops after 2.
*/
#define DHCP_DISC_PROXY_TIMEOUT_SEC 2
//#define DHCP_DISC_PROXY_TIMEOUT_SEC 11 /* as per PXE spec */
/*
* Per the PXE spec, requests are also tried 4 times, but at timeout
* intervals of 1, 2, 3, 4 seconds. To adapt this to an exponential
* backoff timer, we can either do 1, 2, 4, 8, ie. 4 retires with a
* longer interval or start at 0 (0.25s) for 0.25, 0.5, 1, 2, 4,
* ie. one extra try and shorter initial timeouts. iPXE by default
* does a combination of both, starting at 0 and going through the 8
* second timeout.
*/
#define DHCP_REQ_START_TIMEOUT_SEC 0
#define DHCP_REQ_END_TIMEOUT_SEC 10
//#define DHCP_REQ_END_TIMEOUT_SEC 4 /* as per PXE spec */
/*
* A ProxyDHCP offer without PXE options also goes through a request
* phase using these same parameters, but note the early break below.
*/
#define DHCP_PROXY_START_TIMEOUT_SEC 0
#define DHCP_PROXY_END_TIMEOUT_SEC 10
//#define DHCP_PROXY_END_TIMEOUT_SEC 8 /* as per PXE spec */
/*
* A ProxyDHCP request timeout should not induce a failure condition,
* so we always want to break before the above set of timers expire.
* The iPXE default value of 2 breaks at the first timeout after 2
* seconds, which will be after the 2 second timeout.
*/
#define DHCP_REQ_PROXY_TIMEOUT_SEC 2
//#define DHCP_REQ_PROXY_TIMEOUT_SEC 7 /* as per PXE spec */
/*
* Per the PXE spec, a PXE boot server request is also be retried 4
* times at timeouts of 1, 2, 3, 4. iPXE uses the same timeouts as
* discovery, 1, 2, 4, 8, but will move on to the next server if
* available after an elapsed time greater than 3 seconds, therefore
* effectively only sending 3 tries at timeouts of 1, 2, 4.
*/
#define PXEBS_START_TIMEOUT_SEC 1
#define PXEBS_END_TIMEOUT_SEC 10
//#define PXEBS_START_TIMEOUT_SEC 0 /* as per PXE spec */
//#define PXEBS_END_TIMEOUT_SEC 8 /* as per PXE spec */
/*
* Increment to the next PXE Boot server, if available, after this
* this much time has elapsed.
*/
#define PXEBS_MAX_TIMEOUT_SEC 3
//#define PXEBS_MAX_TIMEOUT_SEC 7 /* as per PXE spec */
#include <config/local/dhcp.h>
#endif /* CONFIG_DHCP_H */