Introducción
Este documento describe las expectativas de latencia de un ping o traceroute 'To' o 'From' en una IP de switch Nexus. Una respuesta retrasada del switch es un comportamiento esperado.
Problema
La latencia se observa cuando hacemos ping desde o hacia el switch IP en el switch Nexus.
Nexus-1# ping6 fc00::2
64 bytes from fc00::2: icmp_seq=47 time=12.067 ms
64 bytes from fc00::2: icmp_seq=48 time=12.452 ms
64 bytes from fc00::2: icmp_seq=49 time=12.575 ms
64 bytes from fc00::2: icmp_seq=50 time=12.903 ms
64 bytes from fc00::2: icmp_seq=51 time=14.532 ms
64 bytes from fc00::2: icmp_seq=52 time=15.029 ms
64 bytes from fc00::2: icmp_seq=53 time=15.188 ms
64 bytes from fc00::2: icmp_seq=54 time=15.447 ms
64 bytes from fc00::2: icmp_seq=55 time=15.788 ms
64 bytes from fc00::2: icmp_seq=56 time=16.136 ms
64 bytes from fc00::2: icmp_seq=57 time=16.29 ms
----------------------------------------------------------------------------
Nexus-1# ping 10.1.1.1
64 bytes from 10.1.1.1: icmp_seq=21 ttl=254 time=17.397 ms
64 bytes from 10.1.1.1: icmp_seq=22 ttl=254 time=17.977 ms
64 bytes from 10.1.1.1: icmp_seq=23 ttl=254 time=18.668 ms
64 bytes from 10.1.1.1: icmp_seq=24 ttl=254 time=19.613 ms
64 bytes from 10.1.1.1: icmp_seq=25 ttl=254 time=20.018 ms
64 bytes from 10.1.1.1: icmp_seq=26 ttl=254 time=20.539 ms
64 bytes from 10.1.1.1: icmp_seq=27 ttl=254 time=20.647 ms
64 bytes from 10.1.1.1: icmp_seq=28 ttl=254 time=21.02 ms
64 bytes from 10.1.1.1: icmp_seq=29 ttl=254 time=21.504 ms
64 bytes from 10.1.1.1: icmp_seq=30 ttl=254 time=21.622 ms
Solución
Recomendamos verificar la latencia mediante una prueba de ping entre los dispositivos finales/hosts, en lugar de realizar una prueba de ping para conmutar IP.
- Cuando se recibe una solicitud ICMP al switch, la CPU/supervisor del switch la procesa.
- Los paquetes ICMP son de baja prioridad o tráfico no crítico al switch.
- La CPU/Supervisor del switch necesita procesar otro tráfico crítico como STP BPDU, UDLD, BFD, LACP, OSFP, BGP y otro tráfico del plano de control en prioridad.
- Por lo tanto, cuando hacemos ping en la IP del switch puede haber latencia.
Verificación
- Usando el comando ethanalyzer podemos verificar si hay algún tráfico ICMP inusual recibido en el switch.
- En la siguiente salida, pudimos ver las solicitudes ICMP recibidas de múltiples hosts/fuentes para conmutar IP.
NEXUS# show ip interface brief
IP Interface Status for VRF "default"(1)
Interface IP Address Interface Status
Vlan10 10.1.1.1 protocol-up/link-up/admin-up
NEXUS# ethanalyzer local interface inband display-filter icmp limit-c 0
Capturing on 'ps-inb'
1 2024-05-13 13:05:49.296574516 10.1.1.35 → 10.1.1.1 ICMP 60 Echo (ping) request id=0x0000, seq=0/0, ttl=64
2 2024-05-13 13:05:49.298725978 10.1.1.51 → 10.1.1.1 ICMP 60 Echo (ping) request id=0x0000, seq=0/0, ttl=64
3 2024-05-13 13:05:49.299935463 10.1.1.60 → 10.1.1.1 ICMP 60 Echo (ping) request id=0x0000, seq=0/0, ttl=64
4 2024-05-13 13:05:49.303159980 10.1.1.84 → 10.1.1.1 ICMP 60 Echo (ping) request id=0x0000, seq=0/0, ttl=64
5 2024-05-13 13:05:49.305450067 10.1.1.101 → 10.1.1.1 ICMP 60 Echo (ping) request id=0x0000, seq=0/0, ttl=64
6 2024-05-13 13:05:49.307596053 10.1.1.17 → 10.1.1.1 ICMP 60 Echo (ping) request id=0x0000, seq=0/0, ttl=64
7 2024-05-13 13:05:49.309881152 10.1.1.34 → 10.1.1.1 ICMP 60 Echo (ping) request id=0x0000, seq=0/0, ttl=64
8 2024-05-13 13:05:49.313239980 10.1.1.59 → 10.1.1.1 ICMP 60 Echo (ping) request id=0x0000, seq=0/0, ttl=64
9 2024-05-13 13:05:49.315391183 10.1.1.75 → 10.1.1.1 ICMP 60 Echo (ping) request id=0x0000, seq=0/0, ttl=64
10 2024-05-13 13:05:49.317675859 10.1.1.92 → 10.1.1.1 ICMP 60 Echo (ping) request id=0x0000, seq=0/0, ttl=64
11 2024-05-13 13:05:49.319960319 10.1.1.109 → 10.1.1.1 ICMP 60 Echo (ping) request id=0x0000, seq=0/0, ttl=64
12 2024-05-13 13:05:49.323185627 10.1.1.33 → 10.1.1.1 ICMP 60 Echo (ping) request id=0x0000, seq=0/0, ttl=64
13 2024-05-13 13:05:49.325471951 10.1.1.50 → 10.1.1.1 ICMP 60 Echo (ping) request id=0x0000, seq=0/0, ttl=64
14 2024-05-13 13:05:49.327622826 10.1.1.66 → 10.1.1.1 ICMP 60 Echo (ping) request id=0x0000, seq=0/0, ttl=64
15 2024-05-13 13:05:49.329906456 10.1.1.83 → 10.1.1.1 ICMP 60 Echo (ping) request id=0x0000, seq=0/0, ttl=64
16 2024-05-13 13:05:49.332057200 10.1.1.99 → 10.1.1.1 ICMP 60 Echo (ping) request id=0x0000, seq=0/0, ttl=64
17 2024-05-13 13:05:49.334341820 10.1.1.16 → 10.1.1.1 ICMP 60 Echo (ping) request id=0x0000, seq=0/0, ttl=64
18 2024-05-13 13:05:49.336626919 10.1.1.33 → 10.1.1.1 ICMP 60 Echo (ping) request id=0x0000, seq=0/0, ttl=64
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