This is the mail archive of the
ecos-discuss@sources.redhat.com
mailing list for the eCos project.
Re: Unable to get IP address using do_bootp (found a bug in do_bootp!)
- From: Andrew Lunn <andrew at lunn dot ch>
- To: agyhoo <agyhoo at yahoo dot com>
- Cc: ecos-discuss at ecos dot sourceware dot org
- Date: Mon, 29 Mar 2004 18:51:41 +0200
- Subject: [ECOS] Re: Unable to get IP address using do_bootp (found a bug in do_bootp!)
- References: <20040329153148.4324.qmail@web41302.mail.yahoo.com>
On Mon, Mar 29, 2004 at 07:31:48AM -0800, agyhoo wrote:
> While trying to debug why I was not able to get an IP
> address using do_bootp, I discovered that the do_bootp
> routine does NOT set the broadcast flag in the flags
> field of the bootp protocol header. This is required
> per the BOOTP protocol.
Hold on a minute.....RFC1532 says:
3.1.1 The BROADCAST flag
Normally, BOOTP servers and relay agents attempt to deliver BOOTREPLY
messages directly to a client using unicast delivery. The IP
destination address (in the IP header) is set to the BOOTP 'yiaddr'
address and the link-layer destination address is set to the BOOTP
unable to receive such unicast IP datagrams until they know their own
IP address (thus we have a "chicken and egg" issue). Often, however,
they can receive broadcast IP datagrams (those with a valid IP
broadcast address as the IP destination and the link-layer broadcast
address as the link-layer destination).
If a client falls into this category, it SHOULD set (to 1) the
newly-defined BROADCAST flag in the 'flags' field of BOOTREPLY
messages it generates. This will provide a hint to BOOTP servers and
relay agents that they should attempt to broadcast their BOOTREPLY
messages to the client.
If a client does not have this limitation (i.e., it is perfectly able
to receive unicast BOOTREPLY messages), it SHOULD NOT set the
BROADCAST flag (i.e., it SHOULD clear the BROADCAST flag to 0).
DISCUSSION:
This addition to the protocol is a workaround for old host
implementations. Such implementations SHOULD be modified so
that they may receive unicast BOOTREPLY messages, thus making
use of this workaround unnecessary. In general, the use of
this mechanism is discouraged.
So we should first work out if the network stack really needs it or if
the BOOTP server is doing something wrong. This code has been around
for many years so why has somebody else not found the problem....
Please show us a tcpdump trace of the bootp exchange before and after
your patch.
Andrew
--
Before posting, please read the FAQ: http://ecos.sourceware.org/fom/ecos
and search the list archive: http://ecos.sourceware.org/ml/ecos-discuss