> On Dec 6, 2017, at 10:12 PM, Stephen Hemminger <step...@networkplumber.org> > wrote: > > On Wed, 6 Dec 2017 18:02:21 +0400 > Ilya Matveychikov <matvejchi...@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)? > > > No. > >> ~~~ >> lib/librte_gro/gro_tcp4.c:check_seq_option() >> ... >> /* 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; >> else >> 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?
