Build vlan header in c

Question

I need to build a vlan header. I have code that build eh header (struct ether_header) and it work ok.

/* Ethernet header */
memcpy(eh->ether_shost,src_mac_.data(), 6);
memcpy(eh->ether_dhost,socketAddress.sll_addr , 6);

/* Ethertype field */
eh->ether_type = htons(ETH_P_IP);

I didnt find struct for vlan_eth_header , so i create my own and populate it like this:

struct vlan_ethhdr {
  u_int8_t  ether_dhost[ETH_ALEN];  /* destination eth addr */
  u_int8_t  ether_shost[ETH_ALEN];  /* source ether addr    */
  u_int16_t          h_vlan_proto;
  u_int16_t          h_vlan_TCI;
  u_int16_t ether_type;
 };

    /* Ethernet header */
    memcpy(eh->ether_shost,src_mac_.data(), 6);
    memcpy(eh->ether_dhost,socketAddress.sll_addr , 6);
        eh->h_vlan_proto = htons(0x8100);
        eh->h_vlan_TCI = htons(VLAN_ID);
    /* Ethertype field */
    eh->ether_type = htons(ETH_P_IP);

It seems that i did it wrong. It seems that Wireshak even didnt recognize the packet (the old code sent tcp packet and send them correct). Any advice?

Answer 1

My code to construct VLAN is correct. It dosnt worked for me at the first place , because i forgot to change the size of the packet to be bigger now. Pay attention that TCI is not only VID its included priority and CFI. In my case they both zero , so i dont need to use mask and padding for TCI.