<story><title>Splitting the Ping</title><url>https://blog.benjojo.co.uk/post/ping-with-loss-latency-split</url></story><parent_chain><item><author>great_wubwub</author><text>Everybody is talking about clock accuracy and totally missing that devices in the middle of the network path &lt;i&gt;do not care about responding quickly to pings&lt;/i&gt;. Middle devices are generally routers or firewalls, and their job is to route and firewall, not to respond to a packet as quickly as it comes in. Transit traffic is far more important than processing control plane packets. Devices can add several msec or more in latency by sticking ICMP echo requests and the like in a low-priority queue and getting around to responding eventually.  This will dwarf any gains produced by &amp;quot;the best NTP server&amp;quot;.&lt;p&gt;And no, setting QoS bits on the packet will not help.</text></item></parent_chain><comment><author>walrus01</author><text>Absolutely this. One of the first thing that an ISP&amp;#x27;s NOC will tell a business customer, when they&amp;#x27;re complaining about ICMP loss or high latency to some intermediate-hop seen in a traceroute, is to &lt;i&gt;test against the ICMP loss and latency&amp;#x2F;jitter to an endpoint destination&lt;/i&gt;.&lt;p&gt;Preferably to an endpoint destination that is some sort of server which isn&amp;#x27;t firewalling&amp;#x2F;rate limiting answering ICMP, and not a firewall or router.&lt;p&gt;You can see what looks like terrible loss and jitter to intermediate hops in a traceroute, but traffic to your your VoIP server that is 12.3ms away on the far side of those hops and several AS-to-AS adjacencies, might average 0.00% loss over multi week periods, with less than 0.3ms of jitter range.&lt;p&gt;Customers will also be advised to use other tools that can measure success&amp;#x2F;failure and RTT answer time of other services and daemons running on the endpoint they&amp;#x27;re testing against (at OSI layers 4-7), such as the various ways of measuring DNS lookup query time, or time to curl a sample file from an httpd over TLS1.2&amp;#x2F;1.3, and plot that on a multi day&amp;#x2F;week chart.&lt;p&gt;For their own protection routers and other network equipment with packets flowing &lt;i&gt;through&lt;/i&gt; them deprioritize answering ICMP.</text></comment>
<story><title>Splitting the Ping</title><url>https://blog.benjojo.co.uk/post/ping-with-loss-latency-split</url></story><parent_chain><item><author>great_wubwub</author><text>Everybody is talking about clock accuracy and totally missing that devices in the middle of the network path &lt;i&gt;do not care about responding quickly to pings&lt;/i&gt;. Middle devices are generally routers or firewalls, and their job is to route and firewall, not to respond to a packet as quickly as it comes in. Transit traffic is far more important than processing control plane packets. Devices can add several msec or more in latency by sticking ICMP echo requests and the like in a low-priority queue and getting around to responding eventually.  This will dwarf any gains produced by &amp;quot;the best NTP server&amp;quot;.&lt;p&gt;And no, setting QoS bits on the packet will not help.</text></item></parent_chain><comment><author>bogomipz</author><text>&amp;gt;&amp;quot;Everybody is talking about clock accuracy and totally missing that devices in the middle of the network path do not care about responding quickly to pings. Middle devices are generally routers or firewalls, and their job is to route and firewall, not to respond to a packet as quickly as it comes in.&amp;quot;&lt;p&gt;That&amp;#x27;s not correct. A box in the middle of the network path by definition doesn&amp;#x27;t respond at all to the ping request since it&amp;#x27;s not addressed to them. It&amp;#x27;s simply forwards the IP packet that encapsulates the ICMP echo request towards its destination. As forwarding happens in the data plane this doesn&amp;#x27;t involve the control plane at all. A router with no QoS will forward IP datagrams at the same rate whether they encapsulate TCP, UDP or ICMP.</text></comment>