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udhcpc: add comment about server IP

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Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2011-10-20 14:47:41 +02:00
parent fbca0c68a7
commit 2af2acf9b5
1 changed files with 19 additions and 1 deletions
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20
networking/udhcp/dhcpc.c
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@ -1533,7 +1533,25 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
case INIT_SELECTING:
/* Must be a DHCPOFFER to one of our xid's */
if (*message == DHCPOFFER) {
/* TODO: why we don't just fetch server's IP from IP header? */
/* What exactly is server's IP? There are several values.
* Example DHCP offer captured with tchdump:
*
* 10.34.25.254:67 > 10.34.25.202:68 // IP header's src
* BOOTP fields:
* Your-IP 10.34.25.202
* Server-IP 10.34.32.125 // "next server" IP
* Gateway-IP 10.34.25.254 // relay's address (if DHCP relays are in use)
* DHCP options:
* DHCP-Message Option 53, length 1: Offer
* Server-ID Option 54, length 4: 10.34.255.7 // "server ID"
* Default-Gateway Option 3, length 4: 10.34.25.254 // router
*
* We think that real server IP (one to use in renew/release)
* is one in Server-ID option. But I am not 100% sure.
* IP header's src and Gateway-IP (same in this exaqmple)
* might work too.
* "Next server" and router are definitely wrong ones to use, though...
*/
temp = udhcp_get_option(&packet, DHCP_SERVER_ID);
if (!temp) {
bb_error_msg("no server ID, ignoring packet");