Networking [SOLVED]: How are routes added to the Kernel IP routing table for Red Hat Enterprise Linux?

Networking [SOLVED]: How are routes added to the Kernel IP routing table for Red Hat Enterprise Linux?

Home Forums Networking Networking [SOLVED]: How are routes added to the Kernel IP routing table for Red Hat Enterprise Linux?

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  • #36374

    Anonymous

    QuestionQuestion

    Had a bit of an odd problem that not being able to connect from a Red Hat Enterprise Linux Server release 5.11 (10.110.10.230 on our network) to another machine on the network (10.255.10.82)

    My routing table looked like this

    # /sbin/route 
    Kernel IP routing table
    Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
    169.254.0.0     *               255.255.0.0     U     0      0        0 eth1
    10.0.0.0        *               255.0.0.0       U     0      0        0 eth1
    default         10.110.10.1     0.0.0.0         UG    0      0        0 eth1
    

    I deleted this route …

    10.0.0.0        *               255.0.0.0       U     0      0        0 eth1
    

    with this command…

    /sbin/ip route del 10.0.0.0/8 dev eth1  proto kernel  scope link  src 10.110.10.230
    

    which solved my problem of being able to reach the IP in question, but the route repopulates in the table when I reboot the machine. I thought maybe someone had set a static route on this server, but it doesn’t look like anything is defined in the file

    # cat /etc/sysconfig/networking/devices/ifcfg-eth1 
    # Please read /usr/share/doc/initscripts-*/sysconfig.txt
    # for the documentation of these parameters.
    GATEWAY=10.110.10.1
    TYPE=Ethernet
    DEVICE=eth1
    BOOTPROTO=none
    IPADDR=10.110.10.230
    ONBOOT=yes
    USERCTL=no
    IPV6INIT=no
    PEERDNS=yes
    HWADDR=00:50:56:b9:48:f6
    

    (eth1 is the active adapter on this server)
    There are no files in the /etc/sysconfig/ directory that look to set static routes either.

    So, my question is in what other ways can a route such as this be set, and why is it “sticky” … coming back after a reboot after removing it?

    #36375

    Anonymous

    Accepted AnswerAnswer

    The route 10.0.0.0/8 is added automatically as your eth1 network interface has a static IP address 10.110.10.230 which is defined in ifcfg-eth1. As the NETMASK attribute is not set in the configuration file, RedHat assumes that you’re using the class A default mask (255.0.0.0 or /8 in CIDR notation). So this route is going to be added automatically that’s how it should work.

    If you delete that route with the ip route command, and you can connect with the other machine is thanks to the default gateway 10.110.10.1 so you may have to check if the network mask for your eth1 should be a different one. Check what’s the network mask for your 10.255.10.82 machine or check your router configuration.

    Source: https://serverfault.com/questions/888848/how-are-routes-added-to-the-kernel-ip-routing-table-for-red-hat-enterprise-linux
    Author: Miguel A. C.
    Creative Commons License
    This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

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