Re: [dpdk-dev] How to update the sequence number in TCP packets using DPDK-pktgen?

["Wiles, Keith" <keith.wiles@intel.com>]

> On Oct 9, 2017, at 8:42 AM, Shailja Pandey <csz168117@iitd.ac.in> wrote:
> 
> Hi,
> 
> In the DPDK application, I am maintaining some state and due to that I need to generate the packets with monotonically increasing sequence numbers. As shown in the code below,
> 
> /tip->tcp.seq        = htonl(DEFAULT_PKT_NUMBER);/
> 
> DPDK is putting some default number as a sequence number in the TCP packet and not using as defined by TCP protocol. I tried various workarounds but due to multi-threaded nature of the pktgen application, I am facing some issues and unable to put sequence numbers in increasing order. I tried thread_local and pthread_mutex_lock etc to generate packets with increasing sequence number.
> 
> I am not very sure what am I missing, Please help me in this matter.

The way pktgen was written was for performance, which means I setup the mbufs at start time and do not touch them again till another start command. This causes packets to be sent out of order as I do not know when mbufs are returned to the free pool.

The only way to send a given sequence is to modified each packet as it is sent, which will impact performance. The random mode does just this type of packet mods and it would be a good model to look at if you want to modify the code.

> 
> _Function:_
> 
> void
> pktgen_tcp_hdr_ctor(pkt_seq_t *pkt, tcpip_t *tip, int type __rte_unused)
> {
>         uint16_t tlen;
> 
>         /* Zero out the header space */
>         memset((char *)tip, 0, sizeof(tcpip_t));
> 
>         /* Create the TCP header */
>         tip->ip.src         = htonl(pkt->ip_src_addr.addr.ipv4.s_addr);
>         tip->ip.dst         = htonl(pkt->ip_dst_addr.addr.ipv4.s_addr);
>         tlen                = pkt->pktSize -
>                 (pkt->ether_hdr_size + sizeof(ipHdr_t));
> 
>         tip->ip.len         = htons(tlen);
>         tip->ip.proto       = pkt->ipProto;
> 
>         tip->tcp.sport      = htons(pkt->sport);
>         tip->tcp.dport      = htons(pkt->dport);
> 
> *tip->tcp.seq        = htonl(DEFAULT_PKT_NUMBER);*
> 
>         tip->tcp.ack        = htonl(DEFAULT_ACK_NUMBER);
>         tip->tcp.offset     = ((sizeof(tcpHdr_t) / sizeof(uint32_t)) << 4);     /* Offset in words */
>         tip->tcp.flags      = ACK_FLAG;                                         /* ACK */
>         tip->tcp.window     = htons(DEFAULT_WND_SIZE);
>         tip->tcp.urgent     = 0;
> 
>         tlen                = pkt->pktSize - pkt->ether_hdr_size;
> 
>         tip->tcp.cksum      = cksum(tip, tlen, 0);
> }
> 
> -- 
> 
> Thanks,
> Shailja
> 

Regards,
Keith