[dpdk-dev] A question about GRO neighbor packet matching
matvejchikov at gmail.com
Wed Dec 6 19:38:12 CET 2017
> On Dec 6, 2017, at 10:12 PM, Stephen Hemminger <stephen at networkplumber.org> wrote:
> On Wed, 6 Dec 2017 18:02:21 +0400
> Ilya Matveychikov <matvejchikov at gmail.com> wrote:
>> Hello all,
>> My question is about neighbor packet matching algorithm for TCP. Is it
>> correct to expect that IP packets should have continuous ID enumeration
>> (i.e. iph-next.id = iph-prev.id + 1)?
>> /* check if the two packets are neighbors */
>> tcp_dl0 = pkt0->pkt_len - pkt0->l2_len - pkt0->l3_len - tcp_hl0;
>> if ((sent_seq == (item->sent_seq + tcp_dl0)) &&
>> (ip_id == (item->ip_id + 1)))
>> /* append the new packet */
>> return 1;
>> else if (((sent_seq + tcp_dl) == item->sent_seq) &&
>> ((ip_id + item->nb_merged) == item->ip_id))
>> /* pre-pend the new packet */
>> return -1;
>> return 0;
>> As per RFC791:
>> Identification: 16 bits
>> An identifying value assigned by the sender to aid in assembling the
>> fragments of a datagram.
> The IP header id is meaningless in most TCP sessions.
> Good TCP implementations use PMTU discovery which sets the Don't Fragment bit.
> With DF, the IP id is unused (since no fragmentation).
> Many implementations just send 0 since generating unique IP id requires an
> atomic operation which is potential bottleneck.
So, is my question correct and the code is wrong?
More information about the dev