Hi Raymond, Thanks for providing the references.
@Ben - we had previously discussed the proposed change on the ovs-dev mailing list: https://mail.openvswitch.org/pipermail/ovs-dev/2017-October/339784.html https://mail.openvswitch.org/pipermail/ovs-dev/2017-October/339785.html Thanks, Pradeep -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Raymond Burkholder Sent: Tuesday, January 23, 2018 7:53 AM To: [email protected] Subject: Re: [ovs-dev] [PATCH] bfd: Send BFD packets with DSCP CS6 On 01/22/2018 03:36 PM, Ben Pfaff wrote: > Can you provide a reference to something that helps me understand why > the new value is the "correct" one? This is not my area of expertise > and all I learn from the commit message is an assertion that the new > value is better. here is a short declaration: http://www.ciscopress.com/articles/article.asp?p=357102&seqNum=4 A long dissertation: https://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoS-SRND-Book/QoSIntro.html But in a nutshell: Network engineers create various queue/drop policies based upon precedence. Routing protocols are considered high priority/high precedence. During link saturation events, packets will get dropped. By creating an egress policy where packets marked by CS6 are allowed front-of-the-queue status, one can be sure that hello's from the various protocols arrive when they need to, without delay and without loss. On the other hand, if the hellos are dropped as part of normal traffic operations, then traffic routing will flap, leading to further congestion and drops. CS6 is a 'well known' marker to network engineers. In many vendor's gear, it is automatically assigned to routing protocol packets. Since OVS does not perform queuing, and leaves that to the kernel edge operations, the queue policies can be used to ensure timely egress of the BFD packets during high utilization events. > > Thanks, > > Ben. > > On Mon, Dec 25, 2017 at 04:59:22PM +0000, Venkatesan Pradeep wrote: >> Send BFD packets with TOS value equivalent to DSCP CS6 so that the >> network can apply the right QoS for those packets. This can help >> avoid BFD flaps due to network congestion. >> >> Signed-off-by: Venkatesan Pradeep <[email protected]> >> --- >> lib/bfd.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/lib/bfd.c b/lib/bfd.c >> index 40cd0be..8d291bb 100644 >> --- a/lib/bfd.c >> +++ b/lib/bfd.c >> @@ -612,7 +612,7 @@ bfd_put_packet(struct bfd *bfd, struct dp_packet *p, >> ip->ip_ihl_ver = IP_IHL_VER(5, 4); >> ip->ip_tot_len = htons(sizeof *ip + sizeof *udp + sizeof *msg); >> ip->ip_ttl = MAXTTL; >> - ip->ip_tos = IPTOS_LOWDELAY | IPTOS_THROUGHPUT; >> + ip->ip_tos = IPTOS_PREC_INTERNETCONTROL; >> ip->ip_proto = IPPROTO_UDP; >> put_16aligned_be32(&ip->ip_src, bfd->ip_src); >> put_16aligned_be32(&ip->ip_dst, bfd->ip_dst); >> _______________________________________________ >> dev mailing list >> [email protected] >> https://mail.openvswitch.org/mailman/listinfo/ovs-dev > _______________________________________________ > dev mailing list > [email protected] > https://mail.openvswitch.org/mailman/listinfo/ovs-dev > -- Raymond Burkholder [email protected] https://blog.raymond.burkholder.net -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean. _______________________________________________ dev mailing list [email protected] https://mail.openvswitch.org/mailman/listinfo/ovs-dev _______________________________________________ dev mailing list [email protected] https://mail.openvswitch.org/mailman/listinfo/ovs-dev
