Alignment issues in network programming

[abshah]

I am facing a bit of issue in writing a network software. When I try to send or receive a struct that contains a data type of 8 bytes the next sent or received struct is somehow affected. I have a few things in mind but first I wanted to confirm one thing before I get into debugging.
I am using 32-bit Ubuntu 11.04 (silly me) on a 64-bit x-86 system. Does this has anything to do with the byte alignment problems ?

I am developing a controller to communicate with the Open Flow switch. The openflow protocol defines a set of specs based on which switches are built. The problem is when I try to communicate with the switch everything goes fine until I send or receive a struct that contains a 64 bit date type (uint64_t). The specific structs that are used for sending and receiving features are

/// features req 
struct ofp_header {
    uint8_t version;    /* OFP_VERSION. */
    uint8_t type;       /* One of the OFPT_ constants. */
    uint16_t length;    /* Length including this ofp_header. */
    uint32_t xid;       /* Transaction id associated with this packet.
                           Replies use the same id as was in the request
                           to facilitate pairing. */
};
assert(sizeof(struct ofp_header) == 8); 
 
 
/* Switch features. */
struct ofp_switch_features {
struct ofp_header header;
uint64_t datapath_id; /* Datapath unique ID. The lower 48-bits are for a MAC address, while the upper 16-bits are implementer-defined. */
uint32_t n_buffers; /* Max packets buffered at once. */
uint8_t n_tables; /* Number of tables supported by datapath. */
uint8_t pad[3]; /* Align to 64-bits. */
 
/* Features. */ /* Bitmap of support "ofp_capabilities". */
uint32_t capabilities; /* Bitmap of supported "ofp_action_type"s. */
uint32_t actions; 
 
/* Port info.*/
struct ofp_phy_port ports[0];  /* Port definitions. The number of ports is inferred from the length field in the header. */
};
assert(sizeof(struct ofp_switch_features) == 32);

The problem is when I communicate using any other structs that have data types less than 64-bit everything goes fine. When I receive features reply it shows the right values but after that if i receive any other struct it shows garbage values. Even if i receive features reply again i get garbage values. In short if at any point of code I receive features request or any other struct defined in the specs that has a data type of 64-bit the next structs receive garbage values. The code used for sending and receiving features request is as follows

////// features request and reply  ////////////
 
ofp_header features_req;
 
features_req.version=OFP_VERSION;
features_req.type=OFPT_FEATURES_REQUEST;
features_req.length= htons(sizeof features_req);
features_req.xid = htonl(rcv_hello.xid);
 
 
if (send(connected, &features_req, sizeof(features_req), 0)==-1) {
printf("Error in sending message\n");
exit(-1);
}
printf("features req sent!\n");
 
 
 
ofp_switch_features features_rep={0};
 
if (recv(connected, &features_rep, sizeof(features_rep), 0)==-1) {
printf("Error in receiving message\n");
exit(-1);
}
 
printf("message type : %d\n",features_rep.header.type);
printf("version : %d\n",features_rep.header.version);
printf("message length: %d\n",ntohs(features_rep.header.length));
printf("xid : %d\n",ntohl(features_rep.header.xid));
printf("buffers: %d\n",ntohl(features_rep.n_buffers));
printf("tables: %d\n",features_rep.n_tables);

thanks,
Abdullah