Regarding IP Alias

To Logo,
Thanks for the reply.
I have a setup as follows:
I have a LAN, where I have a Cobalt Cache server which is based on LINUX and ISDN Internet router for Internet connectivity.
Now I want to create one more subnet and want that subnet users also to go through the Cache server. For that purpose I want to give two different subnet IP address to the single ethernet of Cobalt cache server, so that it will serve to two different subnets.
I hope I am clear.

If I can not have routing between eth0:0 and eth0:1, then kindly suggest any ather alternative.

can you post the output of the commands ifconfig and route -n, also a cat  /proc/sys/net/ipv4/ip_forward

whit this info we might be able to help you

BTW... you will be able to route between the too addresses, your cobalt, and any other linux box, can work as a router too

I see no need to use two different addresses for the cobalt.  It sounds like you pretty much want this cobalt to serve as a gateway, or atleast a route for two different subnets.  I would simply create an ip scheme of your own to do this.  You can use 10.0.1.x and 10.0.2.x for your two subnets and give your router, and cobalt ip's in the 10.0.0.x class.  

To MrDaemon,
Following are the commands I have used to configure IP alias. If I try to ping 10.10.10.10 from any other PC on LAN with the IP address 10.10.10.20, I am not able to ping to it and vice versa. Subnet mask used is 255.0.0.0.

COMMANDS used:-

[root@cacheRaq /root]# ifconfig eth0:0 10.10.10.10
[root@cacheRaq /root]# route add -host 10.10.10.10 dev eth0:0
[root@cacheRaq /root]# ping 10.10.10.10
PING 10.10.10.10 (10.10.10.10): 56 data bytes
64 bytes from 10.10.10.10: icmp_seq=0 ttl=64 time=1.3 ms
64 bytes from 10.10.10.10: icmp_seq=1 ttl=64 time=0.7 ms

--- 10.10.10.10 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max = 0.7/1.0/1.3 ms
[root@cacheRaq /root]#  
[root@cacheRaq /root]# ifconfig
lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Bcast:127.255.255.255  Mask:255.0.0.0
          UP BROADCAST LOOPBACK RUNNING  MTU:3584  Metric:1
          RX packets:376 errors:0 dropped:0 overruns:0
          TX packets:376 errors:0 dropped:0 overruns:0
 
eth0      Link encap:Ethernet  HWaddr 00:10:E0:00:2D:D6
          inet addr:192.168.10.100  Bcast:192.168.10.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:32378 errors:0 dropped:0 overruns:0
          TX packets:5 errors:28161 dropped:0 overruns:0
          Interrupt:4
 
eth0:0    Link encap:Ethernet  HWaddr 00:10:E0:00:2D:D6
          inet addr:10.10.10.10  Bcast:10.255.255.255  Mask:255.0.0.0
          UP RUNNING  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0
          TX packets:0 errors:0 dropped:0 overruns:0
 
[root@cacheRaq /root]# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
10.10.10.10     0.0.0.0         255.255.255.255 UH    0      0        0 eth0:0
192.168.10.0    0.0.0.0         255.255.255.0   U     0      0       48 eth0
127.0.0.0       0.0.0.0         255.0.0.0       U     0      0        3 lo
0.0.0.0         192.168.10.200  0.0.0.0         UG    0      0      322 eth0
[root@cacheRaq /root]# cat  /proc/sys/net/ipv4/ip_forward
1
[root@cacheRaq /root]#                                    

To LOGO,
Please tell me what will be my subnet mask for 10.0.1.x and 10.0.2.x network. and what will be for router and cobalt 10.0.0.x network.

Thanks to both of you.
Best regards
Ravi

you need to specify the netmask in the ifconfg command, as you can see in your route -n output ifconfig is assigning a 32 bit mask wich is a multicas mask, so use
root@cacheRaq /root]# ifconfig eth0:0 10.10.10.10 netmask 255.0.0.0

I would also recomend that you use eth0:1 instead of eth0:0 just for clearnes