From mboxrd@z Thu Jan 1 00:00:00 1970 From: Adrien Mazarguil Subject: Re: [PATCH 2/2] app/testpmd: compute checksum in icmpecho replies Date: Fri, 22 May 2015 15:34:34 +0200 Message-ID: <20150522133434.GG26795@6wind.com> References: <1432292852-15701-1-git-send-email-adrien.mazarguil@6wind.com> <1432292852-15701-2-git-send-email-adrien.mazarguil@6wind.com> <555F2420.8010200@6wind.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: dev@dpdk.org To: Olivier MATZ Return-path: Received: from mail-wg0-f41.google.com (mail-wg0-f41.google.com [74.125.82.41]) by dpdk.org (Postfix) with ESMTP id 8AA0AC324 for ; Fri, 22 May 2015 15:34:40 +0200 (CEST) Received: by wgez8 with SMTP id z8so18149592wge.0 for ; Fri, 22 May 2015 06:34:40 -0700 (PDT) Content-Disposition: inline In-Reply-To: <555F2420.8010200@6wind.com> List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" On Fri, May 22, 2015 at 02:42:08PM +0200, Olivier MATZ wrote: > Hi Adrien, Hi Olivier, > On 05/22/2015 01:07 PM, Adrien Mazarguil wrote: > > ICMP echo replies with invalid checksums may be dropped by network nodes or > > ignored by the ping utility. > > > > Signed-off-by: Adrien Mazarguil > > Acked-by: Ivan Boule > > --- > > app/test-pmd/icmpecho.c | 5 +++-- > > 1 file changed, 3 insertions(+), 2 deletions(-) > > > > diff --git a/app/test-pmd/icmpecho.c b/app/test-pmd/icmpecho.c > > index c5933f4..c278baf 100644 > > --- a/app/test-pmd/icmpecho.c > > +++ b/app/test-pmd/icmpecho.c > > @@ -445,7 +445,8 @@ reply_to_icmp_echo_rqsts(struct fwd_stream *fs) > > * - switch IPv4 source and destinations addresses, > > * - set IP_ICMP_ECHO_REPLY in ICMP header. > > * No need to re-compute the IP header checksum. > > - * Reset ICMP checksum. > > + * ICMP checksum is computed by assuming it is valid in the > > + * echo request and not verified. > > */ > > ether_addr_copy(ð_h->s_addr, ð_addr); > > ether_addr_copy(ð_h->d_addr, ð_h->s_addr); > > @@ -454,7 +455,7 @@ reply_to_icmp_echo_rqsts(struct fwd_stream *fs) > > ip_h->src_addr = ip_h->dst_addr; > > ip_h->dst_addr = ip_addr; > > icmp_h->icmp_type = IP_ICMP_ECHO_REPLY; > > - icmp_h->icmp_cksum = 0; > > + icmp_h->icmp_cksum += htons(IP_ICMP_ECHO_REQUEST << 8); > > > I don't think this checksum calculation method is always correct. > > Example of a working case: > > >>> p=Ether(str(Ether()/IP()/ICMP(seq=0))) > >>> p > version=4L ihl=5L tos=0x0 len=28 id=1 flags= frag=0L ttl=64 proto=icmp > chksum=0x7cde src=127.0.0.1 dst=127.0.0.1 options=[] | type=echo-request code=0 chksum=0xf7ff id=0x0 seq=0x0 |>>> > >>> del(p[ICMP].chksum) > >>> p[ICMP].type = 0 > >>> p=Ether(str(p)) > >>> p > version=4L ihl=5L tos=0x0 len=28 id=1 flags= frag=0L ttl=64 proto=icmp > chksum=0x7cde src=127.0.0.1 dst=127.0.0.1 options=[] | type=echo-reply code=0 chksum=0xffff id=0x0 seq=0x0 |>>> > > We have 0xffff - 0xf7ff = 0x0800 > > > Example of a non-working case: > > >>> p=Ether(str(Ether()/IP()/ICMP(seq=0xf800))) > >>> p > version=4L ihl=5L tos=0x0 len=28 id=1 flags= frag=0L ttl=64 proto=icmp > chksum=0x7cde src=127.0.0.1 dst=127.0.0.1 options=[] | type=echo-request code=0 chksum=0xfffe id=0x0 seq=0xf800 |>>> > >>> del(p[ICMP].chksum) > >>> p[ICMP].type = 0 > >>> p=Ether(str(p)) > >>> p > version=4L ihl=5L tos=0x0 len=28 id=1 flags= frag=0L ttl=64 proto=icmp > chksum=0x7cde src=127.0.0.1 dst=127.0.0.1 options=[] | type=echo-reply code=0 chksum=0x7ff id=0x0 seq=0xf800 |>>> > > Here, 0x7ff - 0xfffe != 0x08000 > > > A correct solution (not tested) would be something like: > > uint32_t cksum; > cksum = (~(icmp_h->icmp_cksum)) & 0xffff; > cksum += (~htons(IP_ICMP_ECHO_REQUEST << 8)) & 0xffff; > cksum += (htons(IP_ICMP_ECHO_REPLY << 8)) & 0xffff; > cksum = (cksum & 0xffff) + (cksum >> 16); > cksum = (cksum & 0xffff) + (cksum >> 16); > icmp_h->icmp_cksum = (~cksum) & 0xffff; You're right, my patch is taking too many shortcuts. I'll submit a new patch with your suggestion. Regards, -- Adrien Mazarguil 6WIND