How to display or do eDNS in dpdk packets?-CodePudding

I am using l2fwd-dpdk application from which I can extract 5-tuples, and can see if DNS Packet is present or not.

Now I want to classify the DNS Packet using dpdk, for which I am failing. Here is my code.

 struct rte_udp_hdr *udp_hdr;
 struct dnshdr *dns_hdr;

 if (rte_be_to_cpu_16(udp_hdr->dst_port) == 53)
 {  
 printf("DNS Packet");
 char *dns_hdr = (char *)udp_hdr   sizeof(rte_udp_hdr);
 }

I want to separate

Flags
Rdata
Class
TTL

and save them separately. Is there any way around, I can comfortable to use cpp wrapper as well.

CodePudding user response：

DPDK as of 21.08 does not house any header or structure to typecast to DNS packet. Hence easiest way to solve the issue as mentioned by @wildplasser is to declare your custom DNS header and use it. In your code snippet, you already have struct dnshdr *dns_hdr; So the easier way is to modify your existing code to reflect

 struct rte_udp_hdr *udp_hdr;
 struct dnshdr *dns_hdr;

/* use DPDK mtod API to get the start of ethernet frame */
/* check for packet size, ether type, IP protocol */
/* update udp_hdr to position in the packet */

 if (rte_be_to_cpu_16(udp_hdr->dst_port) == 53)
 {  
 printf("DNS Packet");
 struct dnshdr *dns_hdr = (struct dnshdr *)((char *)udp_hdr   sizeof(rte_udp_hdr));
 }

Note: Possible structure definition code snippet would be

typedef struct {
    uint16_t id;
    uint16_t rd:1;
    uint16_t tc:1;
    uint16_t aa:1;
    uint16_t opcode:4;
    uint16_t qr:1;
    uint16_t rcode:4;
    uint16_t zero:3;
    uint16_t ra:1;
    uint16_t qcount;    /* question count */
    uint16_t ancount;   /* Answer record count */
    uint16_t nscount;   /* Name Server (Autority Record) Count */ 
    uint16_t adcount;   /* Additional Record Count */
} custom_dnshdr;

custom_dnshdr *dns_hdr = (custom_dnshdr *) ((char *)udp_hdr   sizeof(rte_udp_hdr));