Routing Information is Lost at DHCP Re-BOUND (Doc ID 2426395.1)

Last updated on NOVEMBER 23, 2021

Applies to:

Symptoms

Routing information configured in /etc/sysconfig/network-scripts/route-eth#, /etc/rc.d/rc.local or other user scripts is lost in several hours after OS boot, rapid NTP time adjustment, or OS time adjustment by "date" command.

The IP address depends on the routing information is not static configured, but configured via DHCP actually.

For example,

- eth0 is configured via DHCP as /etc/sysconfig/network-scripts/ifcfg-eth0 shows:

DEVICE=eth0
BOOTPROTO=dhcp
TYPE=Ethernet
ONBOOT=yes

- routing information is configured in /etc/rc.d/rc.local as:

ip route add 192.168.3.0/24 via 192.168.1.55 dev eth0

- the initial routing information is:

$ route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.1.1 0.0.0.0 UG 0 0 0 eth0
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
192.168.3.0 192.168.1.55 255.255.255.0 U 0 0 0 eth0

However, after several hours, rapid NTP time adjustment, or OS time adjustment by "date" command, routing information regarding 192.168.3.0/24 configured in /etc/rc.d/rc.local is lost.

$ route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.1.1 0.0.0.0 UG 0 0 0 eth0
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0

Note: in most cases, routing information via dhcp is configured by dhcp servers. However, especially for cloud systems, there are cases that IP address will not be changed but served via dhcp, and some systems need specific routing information which is not served by dhcp server.

The issue exist even if PERSISTENT_DHCLIENT=1 is present in ifcfg-ethX files.

Changes

 N/A

Cause

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