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By default, when an ESX/ESXi host communicates with any destination server on another subnet, it communicates through its default gateway router. If the traffic sent to the default gateway router is destined to be forwarded by that router to another router on the same subnet, the default gateway reply to the ESX/ESXi host with an Internet Control Management Protocol (ICMP) Redirect message. The purpose of this ICMP Redirect message is to tell ESX/ESXi that there is a better route to the destination host and it must instead communicate with the other router. This article provides steps to view the ICMP Redirect route table.
Notes: The consequence of the ICMP Redirect message is that ESX will add a new dynamic host route entry to its routing table. This entry is specifically for the destination host and its route will be the IP of the alternative route. The default gateway of the ESX/ESXi host does not change. To view the route table: Connect to the host with an SSH session. For more information, see Connecting to an ESX host using an SSH client (1019852). Run this command to see the default gateway: # esxcfg-route VMkernel default gateway is 10.27.32.21In this example, the default gateway is 10.27.32.21 Run this command to see the route table: # esxcfg-route -lVMkernel Routes:Network Netmask Gateway Interface ------------- ---------------- ------------- -------------8.8.8.8 255.255.255.255 10.27.47.254 vmk0 10.26.162.185 255.255.255.255 10.27.47.254 vmk0 10.27.32.0 255.255.240.0 Local Subnet vmk0 default 0.0.0.0 10.27.32.21 vmk0 Notes: The preceding output shows that two dynamic host routes have been added, one for each destination host. Instead of using the default gateway of 10.27.32.21, any communication to these two IPs goes through 10.27.47.254. The output of the esxcli command shows that these are manual entries Run this command to see additional output if the route is manual or dynamic: # esxcli network ip route ipv4 listNetwork Netmask Gateway Interface Source------------- --------------- --------- ------default 0.0.0.0 10.27.32.21 vmk0 MANUAL8.8.8.8 255.255.255.255 10.27.47.254 vmk0 MANUAL10.26.162.185 255.255.255.255 10.27.47.254 vmk0 MANUAL10.27.32.0 255.255.240.0 0.0.0.0 vmk0 MANUAL Notes: Normal manual static routes get added to /etc/vmware/esx.conf file so that they persist reboots. Dynamic host route entries created by ICMP Redirect do not get added into esx.conf file, these dynamic host routes are lost when the network or host is restarted. Dynamic host route entries have a timeout of one hour by default, during this timeout period if the ESXi communicates with the destination host the timeout will be reset and restarts its countdown. When more number of dynamic routes created then the timeout period will be shorter than 1 hour. When timeout expires, dynamic route entry will be removed. To manually trigger the clearing of the ICMP Redirect generated routes, restart the network using these commands:#esxcli network ip interface set -e false -i vmk0; esxcli network ip interface set -e true -i vmk0
Connecting to an ESX host using an SSH clientICMP (Internet Control Management Protocol) リダイレクトについてInternet 控制管理协议重定向