10-09-2017
Packet going out of wrong interface due to OS automatically added cache route with lower metric
RHEL 7.0, IPV6
Scenario:
I have routed specific network using network scripts.
1. "ip -6 route show" shows that route has been added. ( with metric 1024)
2. Ping of the specific IP through that route is successful.
3. Now after few days, for some reason, we see that cache route appears for that given destination IP with lower metric ( which is actually trying to take it through interface/bond of the default route.)Ping to that destination IP fails then because packet is going out of wrong interface.
4. If I delete that cache route, again the packet starts going out of the correct interface ( which is not interface of the default route) and ping is successful.
Has anyone faced similar issue with REHL. I am using RHEL 7
Questions:
Q1. In what situation OS will try to route through default, even if static route for specific IP/network exists.
Q2. How to configure the route so that OS does not fall back on default route if specific interface is assigned for a specific ip/network by static configuration. Please note, we can not delete the default route.
Q3. Even if OS is creating cache route for some temporary situation, why is it not detecting that situation has normalized and why it is not deleting the automatically created cache route then. ( assuming that some temporary network side failure caused this issue )
Please note, we are not facing this issue for IPV4. We are facing this with IPV6
Can anyone suggest on how to permanently resolve this situation ?
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routes(4) Kernel Interfaces Manual routes(4)
NAME
routes - Specifies Internet routing information to the routing tables
SYNOPSIS
/etc/routes
DESCRIPTION
Static routes can be defined in the /etc/routes file. The /etc/routes file identifies static routes that are automatically added to the
network routing tables with the /usr/sbin/route add command. The /sbin/init.d/route script contains the /usr/sbin/route add command that
is executed for each entry in the /etc/routes file when the network is restarted on the system or the system is rebooted.
The general format of an entry in the /etc/routes file is: Dest Name1 Name2
The following is a brief description of each element in an /etc/routes file entry: A keyword that indicates whether the route is to a net-
work or to a host. The two possible keywords are -net and -host. The name or address of the destination network or host. Name1 can be
either a symbolic name (as used in the /etc/hosts or /etc/networks file) or an Internet address specified in dotted-decimal format. The
name or address of the gateway host to which messages should be forwarded. Name2 can be either a symbolic name (as used in the /etc/hosts
file) or an Internet address specified in dotted-decimal format.
The routes file is a Context-Dependent Symbolic Link (CDSL) and must be maintained as such. See the System Administration manual for more
information.
EXAMPLES
To specify a route to a network through a gateway host with an entry in the /etc/routes file, enter:
-net net2 host4
This example specifies a route to a network, net2, through the gateway host4. To specify a route to a host through a gateway host
with an entry in the /etc/routes file, enter:
-host host2 host4
This example specifies a route to a host, host2, through the gateway host4. To specify a route to a default gateway host with an
entry in the /etc/routes file, enter:
default 130.9.0.5
This example specifies a route to a default gateway with an Internet address of 130.9.0.5.
FILES
Contains the /usr/sbin/routed add command.
RELATED INFORMATION
Commands: route(8)
Daemons: gated(8), routed(8)
Files: gated.conf(4)
Network Administration delim off
routes(4)