Danny Mayer wrote: >Why do you need to have QOS for NTP? > >Danny > >
I created a bug and attached the patches: http://bugs.ntp.isc.org/show_bug.cgi?id=752 Comment #4 should answer this question: ======== Quoting Section four of RFC-2474: 4. Historical Codepoint Definitions and PHB Requirements The DS field will have a limited backwards compatibility with current practice, as described in this section. Backwards compatibility is addressed in two ways. First, there are per-hop behaviors that are already in widespread use (e.g., those satisfying the IPv4 Precedence queueing requirements specified in [RFC1812]), and we wish to permit their continued use in DS-compliant nodes. In addition, there are some codepoints that correspond to historical use of the IP Precedence field and we reserve these codepoints to map to PHBs that meet the general requirements specified in Sec. 4.2.2.2, though the specific differentiated services PHBs mapped to by those codepoints MAY have additional specifications. No attempt is made to maintain backwards compatibility with the "DTR" or TOS bits of the IPv4 TOS octet, as defined in [RFC791]. That last sentence is the clincher, since that's how NTP 4.2.2 currently tags packets (using the obsolete DTR bits). The fix that I've attached currently leaves the markings as they are, but to bring a minimum of compliance to what the Internet uses, we really should default the tagging to Class Selector 6 (cs6), i.e. 0xc0 (what netinet/ip.h calls IPTOS_PREC_INTERNETCONTROL). The fix for that would be: #if defined(HAVE_IPTOS_SUPPORT) /* set IP_TOS to minimize packet delay */ +# if defined(IPTOS_PREC_INTERNETCONTROL) +int tos = IPTOS_PREC_INTERNETCONTROL; +# else int tos = IPTOS_LOWDELAY; +# endif #endif which is eminently reasonable, since there is no universally agreed upon DSCP (differentiated services code point) value for NTP at this time. I note also that this is the current value that Cisco IOS routers use, and they are largely QoS-aware. ======== _______________________________________________ questions mailing list [email protected] https://lists.ntp.isc.org/mailman/listinfo/questions
