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Special Forums IP Networking Packet going out of wrong interface due to OS automatically added cache route with lower metric Post 303004795 by msr1981 on Monday 9th of October 2017 07:34:34 AM
Old 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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ROUTE.CONF(5)						      BSD File Formats Manual						     ROUTE.CONF(5)

NAME
route.conf -- static routes config file DESCRIPTION
The route.conf file is read by the staticroute rc.d script during system start-up and shutdown, and is intended for adding and removing static routes. FILE FORMAT Lines starting with a hash ('#') are comments and ignored. Lines starting with a plus sign ('+') are run during start-up, while lines start- ing with a minus sign ('-') are run during system shutdown. If a line starts with a '!', the rest of the line will get evaluated as a shell script fragment. All other lines are passed to route(8). During start-up, they are passed behind a ``route add -'' command and during shut- down behind a ``route delete -'' command. FILES
/etc/route.conf The route.conf file resides in /etc. /etc/rc.d/staticroute rc.d(8) script that parses route.conf. EXAMPLES
In this example, the interface for the desired routing changes is set, the IP address on that interface is determined, and a route is added during startup, or deleted during system shutdown. # Set interface and determine current IP address for added route. !ifname=bnx0 !ipaddr=$(/sbin/ifconfig ${ifname} | awk '$1 == "inet" {print $2}') net 10.10.1 -interface ${ipaddr} In this example, IP forwarding is turned on during start-up, and a static route added for 192.168.2.0. During system shutdown, the route is removed and IP forwarding turned off. # Turn on/off IP forwarding. +sysctl -w net.inet.ip.forwarding=1 -sysctl -w net.inet.ip.forwarding=0 net 192.168.2.0 -netmask 255.255.255.0 192.168.150.2 SEE ALSO
rc.conf(5), rc(8), route(8) BSD
May 1, 2012 BSD
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