[CentOS] Network routes

Tue Jan 29 22:38:02 UTC 2008
Ross S. W. Walker <rwalker at medallion.com>

Jason Pyeron wrote:
> 
> I am unable to ping NE.TW.RKB.IP1 from an outside network. 
> Other machines
> which do not have access or routes for NET.WOR.KA.0 respond just fine.
> 
> How do I get it to respond on both NET.WOR.KA.0 and 
> NE.TW.RKB.0 given all
> default traffic should go through  NET.WOR.KA.1  unless it is 
> in reply to
> traffic from NE.TW.RKB.1 or there is an outage.
> 
> [root at host20 ~]# route -n
> Kernel IP routing table
> Destination     Gateway         Genmask         Flags Metric 
> Ref    Use
> Iface
> NET.WOR.KA.0    0.0.0.0         255.255.255.0   U     0      
> 0        0 eth1
> 192.168.1.0     0.0.0.0         255.255.255.0   U     0      
> 0        0 eth0
> NE.TW.RKB.0     0.0.0.0         255.255.255.0   U     0      
> 0        0 eth0
> 169.254.0.0     0.0.0.0         255.255.0.0     U     0      
> 0        0 eth1
> 0.0.0.0         NET.WOR.KA.1    0.0.0.0         UG    0      
> 0        0 eth1
> 0.0.0.0         NE.TW.RKB.1     0.0.0.0         UG    20     
> 0        0 eth0
> 
> [root at host20 ~]# ifconfig
> eth0      Link encap:Ethernet  HWaddr 00:17:31:0F:04:AE
>           inet addr:NE.TW.RKB.IP1  Bcast:NE.TW.RKB.255  
> Mask:255.255.255.0
> eth0:pn   Link encap:Ethernet  HWaddr 00:17:31:0F:04:AE
>           inet addr:192.168.1.20  Bcast:192.168.1.255  
> Mask:255.255.255.0
> eth1      Link encap:Ethernet  HWaddr 00:01:03:E9:42:D0
>           inet addr:NET.WOR.KA.IP2  Bcast:NET.WOR.KA.255  
> Mask:255.255.255.0
> lo        Link encap:Local Loopback
>           inet addr:127.0.0.1  Mask:255.0.0.0
> 

You can have only 1 default route.

You can use RIP or some other routing protocol to
advertise defualt routes to the host from the
gateways based upon route availability or weight,
or you can deploy reverse NAT'ing on the gateways
so external IPs will be masqueraded as the
internal IP of the gateway and thus be routed to
the appropriate gateway based on which IP they
arrived on.

-Ross

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