2af2acf9b
Denys Vlasenko
2011-10-20
Subject
udhcpc: add comment about server IP
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networking/udhcp/dhcpc.c+19 -1
| @@ -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"); | |