[ipxe-devel] [RESEND PATCH] [dhcp] More spec compliant DHCP/PXE timeouts

[Jarrod Johnson]

For what it is worth, if I remember I plan to pull this into the xNBA
repository when I next merge (I think that'll be tomorrow).  I second that
this is an issue in a lot of poorly configured environments.  Surprised to
see *VMs* so badly afflicted, but switch timeouts with block-by-default
spanning tree frequently are fatal to iPXE as-is.


On Mon, Feb 17, 2014 at 4:20 PM, Alex Williamson <alex.williamson at redhat.com
> wrote:

> For discovery, both the DHCP and PXE specs suggest timeouts of 4, 8,
> 16, and 32 seconds.  This gives us a maximum timeout of 60 seconds,
> versus the current timeout of 15 seconds at timeouts of 1, 2, 4, and
> 8 seconds.
>
> On the request phase, the specs are quite different.  RFC2131 for DHCP
> suggests the same intervals as above for discovery, while the PXE spec
> recommends intervals of 1, 2, 3, and 4 seconds.  Our timer only wants
> to do exponential back-off, so we compromise and adjust to intervals
> of 1, 2, 4, and 8 seconds.  PXE boot server discovery appears to want
> the same timeouts as the DHCP request phase.
>
> Signed-off-by: Alex Williamson <alex.williamson at redhat.com>
> ---
>
> I posted this previously[1] and prior to that also sent a question to
> the list asking why iPXE uses the non-spec compliant DHCP timeouts
> that it does[2].  There was some support for this patch[3], but it was
> never commited.  My ping a couple weeks later also came up short[4].
> We do have customers complaining about this and unable to reliably
> boot virtual machines over their production network due to these short
> timeouts.  Could we consider a patch like below, or any sort of
> re-implementation of it, to make iPXE DHCP behave more in accordance
> with spec defined timeouts?  Thanks
>
> [1] http://lists.ipxe.org/pipermail/ipxe-devel/2013-June/002573.html
> [2] http://lists.ipxe.org/pipermail/ipxe-devel/2013-June/002562.html
> [3] http://lists.ipxe.org/pipermail/ipxe-devel/2013-June/002576.html
> [4] http://lists.ipxe.org/pipermail/ipxe-devel/2013-June/002610.html
>
>  src/include/ipxe/dhcp.h |    4 ----
>  src/net/udp/dhcp.c      |   22 +++++++++++++---------
>  2 files changed, 13 insertions(+), 13 deletions(-)
>
> diff --git a/src/include/ipxe/dhcp.h b/src/include/ipxe/dhcp.h
> index bcfb85c..595f0c1 100644
> --- a/src/include/ipxe/dhcp.h
> +++ b/src/include/ipxe/dhcp.h
> @@ -639,10 +639,6 @@ struct dhcphdr {
>   */
>  #define DHCP_MIN_LEN 552
>
> -/** Timeouts for sending DHCP packets */
> -#define DHCP_MIN_TIMEOUT ( 1 * TICKS_PER_SEC )
> -#define DHCP_MAX_TIMEOUT ( 10 * TICKS_PER_SEC )
> -
>  /** Maximum time that we will wait for ProxyDHCP responses */
>  #define PROXYDHCP_MAX_TIMEOUT ( 2 * TICKS_PER_SEC )
>
> diff --git a/src/net/udp/dhcp.c b/src/net/udp/dhcp.c
> index e6d3edd..87c8d6e 100644
> --- a/src/net/udp/dhcp.c
> +++ b/src/net/udp/dhcp.c
> @@ -171,8 +171,9 @@ struct dhcp_session_state {
>         void ( * expired ) ( struct dhcp_session *dhcp );
>         /** Transmitted message type */
>         uint8_t tx_msgtype;
> -       /** Apply minimum timeout */
> -       uint8_t apply_min_timeout;
> +       /** Timer parameters (seconds) */
> +       unsigned long min_timeout;
> +       unsigned long max_timeout;
>  };
>
>  static struct dhcp_session_state dhcp_state_discover;
> @@ -272,9 +273,8 @@ static void dhcp_set_state ( struct dhcp_session *dhcp,
>         dhcp->state = state;
>         dhcp->start = currticks();
>         stop_timer ( &dhcp->timer );
> -       dhcp->timer.min_timeout =
> -               ( state->apply_min_timeout ? DHCP_MIN_TIMEOUT : 0 );
> -       dhcp->timer.max_timeout = DHCP_MAX_TIMEOUT;
> +       dhcp->timer.min_timeout = state->min_timeout * TICKS_PER_SEC;
> +       dhcp->timer.max_timeout = state->max_timeout * TICKS_PER_SEC;
>         start_timer_nodelay ( &dhcp->timer );
>  }
>
> @@ -447,7 +447,8 @@ static struct dhcp_session_state dhcp_state_discover =
> {
>         .rx                     = dhcp_discovery_rx,
>         .expired                = dhcp_discovery_expired,
>         .tx_msgtype             = DHCPDISCOVER,
> -       .apply_min_timeout      = 1,
> +       .min_timeout            = 4,
> +       .max_timeout            = 32,
>  };
>
>  /**
> @@ -584,7 +585,8 @@ static struct dhcp_session_state dhcp_state_request = {
>         .rx                     = dhcp_request_rx,
>         .expired                = dhcp_request_expired,
>         .tx_msgtype             = DHCPREQUEST,
> -       .apply_min_timeout      = 0,
> +       .min_timeout            = 1,
> +       .max_timeout            = 8,
>  };
>
>  /**
> @@ -685,7 +687,8 @@ static struct dhcp_session_state dhcp_state_proxy = {
>         .rx                     = dhcp_proxy_rx,
>         .expired                = dhcp_proxy_expired,
>         .tx_msgtype             = DHCPREQUEST,
> -       .apply_min_timeout      = 0,
> +       .min_timeout            = 1,
> +       .max_timeout            = 8,
>  };
>
>  /**
> @@ -832,7 +835,8 @@ static struct dhcp_session_state dhcp_state_pxebs = {
>         .rx                     = dhcp_pxebs_rx,
>         .expired                = dhcp_pxebs_expired,
>         .tx_msgtype             = DHCPREQUEST,
> -       .apply_min_timeout      = 1,
> +       .min_timeout            = 1,
> +       .max_timeout            = 8,
>  };
>
>
>  /****************************************************************************
>
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