dhcpv6: omit IA_NA on Request

Omit IA_NA on Request if not present on Solicit, which is against RFC7550,
but turns out some broken ISPs don't like this.
See https://github.com/openwrt/odhcp6c/issues/144

Closes: https://github.com/openwrt/odhcp6c/issues/144
Link: https://github.com/openwrt/odhcp6c/pull/147
Fixes: 63461f64d4c1 ("dhcpv6: always include IA_NA and IA_PD in Request message if requested")
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

diff --git a/src/dhcpv6.c b/src/dhcpv6.c
index bb9ac13b6a1046f6171759188d106924617c9e47..49636821c21b7ec85ecd11930c52b58ff64c2915 100644 (file)
--- a/src/dhcpv6.c
+++ b/src/dhcpv6.c
@@ -957,11 +957,38 @@ static void dhcpv6_send(enum dhcpv6_msg req_msg_type, uint8_t trid[3], uint32_t
                cnt = IOV_HDR_IA_NA;
 
        // Disable IAs if not used
-       if (req_msg_type != DHCPV6_MSG_SOLICIT && req_msg_type != DHCPV6_MSG_REQUEST && ia_na_len == 0)
+       if (na_mode == IA_MODE_NONE) {
                iov[IOV_HDR_IA_NA].iov_len = 0;
+       } else if (ia_na_len == 0) {
+               /* RFC7550 §4.2
+                *    Solution: a client SHOULD accept Advertise messages, even
+                *    when not all IA option types are being offered. And, in
+                *    this case, the client SHOULD include the not offered IA
+                *    option types in its Request. A client SHOULD only ignore
+                *    an Advertise message when none of the requested IA
+                *    options include offered addresses or delegated prefixes.
+                *    Note that ignored messages MUST still be processed for
+                *    SOL_MAX_RT and INF_MAX_RT options as specified in
+                *    [RFC7083].
+                */
 
-       if (na_mode == IA_MODE_NONE)
-               iov[IOV_HDR_IA_NA].iov_len = 0;
+               switch (req_msg_type) {
+               case DHCPV6_MSG_REQUEST:
+                       /* Some broken ISPs won't behave properly if IA_NA is
+                        * sent on Requests when they have provided an empty
+                        * IA_NA on Advertise.
+                        * Therefore we don't comply with RFC7550 and omit
+                        * IA_NA as a workaround.
+                        */
+                       iov[IOV_HDR_IA_NA].iov_len = 0;
+                       break;
+               case DHCPV6_MSG_SOLICIT:
+                       break;
+               default:
+                       iov[IOV_HDR_IA_NA].iov_len = 0;
+                       break;
+               }
+       }
 
        if ((req_msg_type != DHCPV6_MSG_SOLICIT && req_msg_type != DHCPV6_MSG_REQUEST) ||
                        !(client_options & DHCPV6_ACCEPT_RECONFIGURE))