Wise people learn when they can; fools learn when they must - Arthur Wellesley

Thursday, 23 February 2017

RHEL6-(10) -ROUTES & DEFAULT GATEWAY –P2


RHEL6-(10)-ROUTES & DEFAULT GATEWAY                             -P2

Under Routes & Default Gateway:

ROUTES & DEFAULT GATEWAY –P1
ROUTES & DEFAULT GATEWAY –P2
ROUTES & DEFAULT GATEWAY –P3

In UNIX systems routing table consists the information about packet forwarding.


Route add
Route delete
Making route persistent
Default route configuration

[root@rhel6-server ~]# ip route show
192.168.234.0/24 dev eth1  proto kernel  scope link  src 192.168.234.146  metric 1
192.168.234.0/24 dev eth2  proto kernel  scope link  src 192.168.234.147  metric 1
192.168.110.0/24 dev eth0  proto kernel  scope link  src 192.168.110.137  metric 1
192.168.110.0/24 dev eth3  proto kernel  scope link  src 192.168.110.135  metric 1
default via 192.168.110.1 dev eth0  proto static


[root@rhel6-server ~]# netstat -nr
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
192.168.234.0   0.0.0.0         255.255.255.0   U         0 0          0 eth1
192.168.234.0   0.0.0.0         255.255.255.0   U         0 0          0 eth2
192.168.110.0   0.0.0.0         255.255.255.0   U         0 0          0 eth0
192.168.110.0   0.0.0.0         255.255.255.0   U         0 0          0 eth3
0.0.0.0         192.168.110.1   0.0.0.0         UG        0 0          0 eth0

Now what I want is, the traffic from 192.168.234.0 should follow its own default gateway 192.168.234.2 via eth1.

[root@rhel6-server ~]# ip route add 192.168.234.0/24 via 192.168.234.2 dev eth1

[root@rhel6-server /]# ip route show
192.168.234.0/24 via 192.168.234.2 dev eth1
192.168.234.0/24 dev eth2  proto kernel  scope link  src 192.168.234.147  metric 1
192.168.234.0/24 dev eth1  proto kernel  scope link  src 192.168.234.146  metric 1
192.168.110.0/24 dev eth3  proto kernel  scope link  src 192.168.110.135  metric 1
192.168.110.0/24 dev eth0  proto kernel  scope link  src 192.168.110.137  metric 1
default via 192.168.110.1 dev eth0  proto static

[root@rhel6-server /]# netstat -nr
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
192.168.234.0   192.168.234.2   255.255.255.0   UG        0 0          0 eth1
192.168.234.0   0.0.0.0         255.255.255.0   U         0 0          0 eth2
192.168.234.0   0.0.0.0         255.255.255.0   U         0 0          0 eth1
192.168.110.0   0.0.0.0         255.255.255.0   U         0 0          0 eth3
192.168.110.0   0.0.0.0         255.255.255.0   U         0 0          0 eth0
0.0.0.0         192.168.110.1   0.0.0.0         UG        0 0          0 eth0

Changes are effective, but are they persistent…??

NO……

Just,
[root@rhel6-server /]# service network restart

All gone.

As recommended I created a file,

[root@rhel6-server /]# vi /etc/sysconfig/network-scripts/route-eth1
GATEWAY0=192.168.234.2
NETMASK0=255.255.255.0
ADDRESS0=192.168.234.0

And restart network, but no luck. Then I did,

[root@rhel6-server /]# cat /etc/sysconfig/network-scripts/route-eth1
#GATEWAY0=192.168.234.2
#NETMASK0=255.255.255.0
#ADDRESS0=192.168.234.0
192.168.234.0/24 via 192.168.234.2 dev eth1 çç

And restart network, but again no luck. Then I did,

[root@rhel6-server /]# vi /etc/sysconfig/static-routes
any net 192.168.234.0 netmask 255.255.255.0 gw 192.168.234.2 eth1

[root@rhel6-server /]# service network restart

And,

[root@rhel6-server /]# netstat -nr
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
192.168.234.0   192.168.234.2   255.255.255.0   UG        0 0          0 eth1
192.168.234.0   0.0.0.0         255.255.255.0   U         0 0          0 eth2
192.168.234.0   0.0.0.0         255.255.255.0   U         0 0          0 eth1
192.168.110.0   0.0.0.0         255.255.255.0   U         0 0          0 eth3
192.168.110.0   0.0.0.0         255.255.255.0   U         0 0          0 eth0
0.0.0.0         192.168.110.1   0.0.0.0         UG        0 0          0 eth0

Now it is permanent.

Next What…??

Let’s do it again,

ROUTE CONFIGURATION:

ip route [ add | del | change | append | replace ] destination-address

ROUTE ADD:

Single IP

[root@rhel6-server /]# ip route add 192.168.234.146 via 192.168.234.2 dev eth1

Whole subnet

[root@rhel6-server /]# ip route add 192.168.234.0/24 via 192.168.234.2 dev eth2

We can make it persistent by,

[root@rhel6-server /]# vi /etc/sysconfig/static-routes
any net 192.168.234.0 netmask 255.255.255.0 gw 192.168.234.2 eth1
any net 192.168.110.0 netmask 255.255.255.0 gw 192.168.110.1 eth3

[root@rhel6-server /]# service network restart

[root@rhel6-server /]# netstat -nr
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
192.168.234.0   192.168.234.2   255.255.255.0   UG        0 0          0 eth1
192.168.234.0   0.0.0.0         255.255.255.0   U         0 0          0 eth2
192.168.234.0   0.0.0.0         255.255.255.0   U         0 0          0 eth1
192.168.110.0   192.168.110.1   255.255.255.0   UG        0 0          0 eth3
192.168.110.0   0.0.0.0         255.255.255.0   U         0 0          0 eth3
192.168.110.0   0.0.0.0         255.255.255.0   U         0 0          0 eth0
0.0.0.0         192.168.110.1   0.0.0.0         UG        0 0          0 eth0

We can also do,

Either,

[root@rhel6-server /]# vi /etc/sysconfig/network-scripts/route-eth1
GATEWAY0=192.168.234.2
NETMASK0=255.255.255.0
ADDRESS0=192.168.234.0

Or,

[root@rhel6-server /]# vi /etc/sysconfig/network-scripts/route-eth1
192.168.234.0/24 via 192.168.234.2 dev eth1

This method (route-dev_name) did not work for me.

ROUTE DELETE:

Referring o/p from above “netstat –nr”

[root@rhel6-server /]# ip route delete 192.168.234.0/24 via 192.168.234.2 dev eth1

[root@rhel6-server /]# netstat -nr
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
192.168.234.0   0.0.0.0         255.255.255.0   U         0 0          0 eth2
192.168.234.0   0.0.0.0         255.255.255.0   U         0 0          0 eth1
192.168.110.0   192.168.110.1   255.255.255.0   UG        0 0          0 eth3
192.168.110.0   0.0.0.0         255.255.255.0   U         0 0          0 eth3
192.168.110.0   0.0.0.0         255.255.255.0   U         0 0          0 eth0
0.0.0.0         192.168.110.1   0.0.0.0         UG        0 0          0 eth0

Delete any corresponding entry if any from “route-eth1” or “static-routes” file to make it persistent.

[root@rhel6-server /]# ip route delete 192.168.234.0/24
[root@rhel6-server /]# netstat -nr
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
192.168.234.0   0.0.0.0         255.255.255.0   U         0 0          0 eth1
192.168.110.0   192.168.110.1   255.255.255.0   UG        0 0          0 eth3
192.168.110.0   0.0.0.0         255.255.255.0   U         0 0          0 eth3
192.168.110.0   0.0.0.0         255.255.255.0   U         0 0          0 eth0
0.0.0.0         192.168.110.1   0.0.0.0         UG        0 0          0 eth0

[root@rhel6-server /]# ip route delete 192.168.234.0/24 dev eth1

DEFAULT ROUTE REPLACE:

[root@rhel6-server /]# ip route replace default via 192.168.234.2 dev eth1
[root@rhel6-server /]# netstat -nr
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
192.168.234.0   0.0.0.0         255.255.255.0   U         0 0          0 eth2
192.168.234.0   0.0.0.0         255.255.255.0   U         0 0          0 eth1
192.168.110.0   192.168.110.1   255.255.255.0   UG        0 0          0 eth3
192.168.110.0   0.0.0.0         255.255.255.0   U         0 0          0 eth3
192.168.110.0   0.0.0.0         255.255.255.0   U         0 0          0 eth0
0.0.0.0         192.168.234.2   0.0.0.0         UG        0 0          0 eth1


[root@rhel6-server /]# ip route replace via 192.168.110.1 dev eth0
[root@rhel6-server /]# netstat -nr
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
192.168.234.0   0.0.0.0         255.255.255.0   U         0 0          0 eth2
192.168.234.0   0.0.0.0         255.255.255.0   U         0 0          0 eth1
192.168.110.0   192.168.110.1   255.255.255.0   UG        0 0          0 eth3
192.168.110.0   0.0.0.0         255.255.255.0   U         0 0          0 eth3
192.168.110.0   0.0.0.0         255.255.255.0   U         0 0          0 eth0
0.0.0.0         192.168.110.1   0.0.0.0         UG        0 0          0 eth0

DEFAULT GATEWAY CONFIGURATION:

[root@rhel6-server /]# route del default gw 192.168.110.1
“OR”
[root@rhel6-server /]# ip route del default via 192.168.110.1

[root@rhel6-server /]# netstat -nr
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
192.168.110.0   192.168.110.1   255.255.255.0   UG        0 0          0 eth3
192.168.110.0   0.0.0.0         255.255.255.0   U         0 0          0 eth3
192.168.110.0   0.0.0.0         255.255.255.0   U         0 0          0 eth0

[root@rhel6-server /]# route -Cn
Kernel IP routing cache
Source          Destination     Gateway         Flags Metric Ref    Use Iface
192.168.110.1   192.168.110.137 192.168.110.137 l     0      0      549 lo
192.168.110.137 192.168.110.1   192.168.110.1         0      1        0 eth3

“-C” lists the kernel’s routing cache information.

[root@rhel6-server /]# route add default gw 192.168.110.1
“OR”
[root@rhel6-server /]# ip route add default via 192.168.110.1

[root@rhel6-server /]# netstat -nr
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
192.168.110.0   192.168.110.1   255.255.255.0   UG        0 0          0 eth3
192.168.110.0   0.0.0.0         255.255.255.0   U         0 0          0 eth3
192.168.110.0   0.0.0.0         255.255.255.0   U         0 0          0 eth0
0.0.0.0         192.168.110.1   0.0.0.0         UG        0 0          0 eth3

[root@rhel6-server /]# route -Cn
Kernel IP routing cache
Source          Destination     Gateway         Flags Metric Ref    Use Iface
192.168.110.137 192.168.110.1   192.168.110.1         0      1        0 eth3
192.168.110.1   192.168.110.137 192.168.110.137 l     0      0       30 lo
192.168.110.1   192.168.110.255 192.168.110.255 bl    0      0        1 lo

CONTINUE………..





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