[CentOS] Re: Network routes

[Scott Silva]

on 1/29/2008 2:53 PM Jason Pyeron spake the following:
>  
> 
>> -----Original Message-----
>> From: centos-bounces at centos.org 
>> [mailto:centos-bounces at centos.org] On Behalf Of Ross S. W. Walker
>> Sent: Tuesday, January 29, 2008 17:38
>> To: CentOS mailing list
>> Subject: RE: [CentOS] Network routes
>>
>> 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
>>
> 
> But I have 2 physical network cards, on 2 different networks. Should they
> not both have default routes?
> 
You would think so, but it will confuse the system so bad that traffic won't 
know where to go. The default route is the route that packets need to take to 
leave your network to enter the outside world. Every thing under your control 
should have static routes of some kind, or a routing daemon.

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