Description

This article guides you on how to troubleshoot and isolate the latency issue seen in the network with Juniper devices.

Symptoms

Latency observed on the ping towards the internet. For instance while pinging 8.8.8.8 we are getting a latency of 100ms.
While normally the ping response is 30 ms.

Solution

1. First step is to check the traceroute towards the internet and check how many hops we have in between.

>traceroute 8.8.8.8

1  jpsjc-app-fw1-reth2-3005.jnpr.net (10.104.8.1)  0.512 ms  0.492 ms  0.465 ms
 2  jpsjc-core-gw1-et-0-0-2-0.jnpr.net (172.29.158.129)  0.801 ms  0.701 ms  0.660 ms
 3  * * *
 4  jpsjc-ext-gw1-et-1-3-1-vrrp.jnpr.net (66.129.239.5)  1.230 ms  1.239 ms  1.240 ms
 5  eqixsj-google-gige.google.com (206.223.116.21)  1.336 ms  1.240 ms  1.525 ms
 6  192.178.87.169 (192.178.87.169)  2.530 ms 142.251.254.241 (142.251.254.241)  1.621 ms 192.178.87.169 (192.178.87.169)  3.759 ms
 7  209.85.243.113 (209.85.243.113)  1.573 ms 108.170.235.209 (108.170.235.209)  1.812 ms 142.251.224.175 (142.251.224.175)  1.643 ms
 8  dns.google (8.8.8.8)  1.797 ms  1.877 ms  2.188 ms

Please note that we cannot rely on the traceroute output to confirm the latency as the latency mentioned in this output is the average time taken by each node in the path to respond to ICMP ping which is a control path packet. So we may see higher latency depending on CPU load of the individual device in the path.

2. If there is a secondary ISP link, try to failover to the secondary link and check if the latency persists on the secondary link or if it happens only in the primary link.

3. Get access to each of the intermediate router and check for any ingress/egress drops on the interfaces.

4. Go to the next hop and then try to see what is the latency towards the internet. If the second hop is showing a ping latency of 30ms towards internet then the problem is between the first and the second hop.

Similarly we can move to other devices in the path and determine the ping latency to isolate and troubleshoot.

Modification History

2024-03-28 : Article Created
2024-08-21 : Making article public, basic formatting check done.

2026-02-27 : Updated category