Multiple IP addresses for the same interface...

[Mani Sridhar <linux@xxxxxxxxxxxx>]

Dear Luggies
	My college now has a 512 kbps connection to the Internet. Given
the fact that the earlier 64 kbps microwave link was shared by over 250
users, this is a huge improvement. The 512 kbps link is through a DOT
leased line. 
	We have a Cisco 2500 router with 2 interfaces, one connected to a
radio modem ( for the 64kbps microwave link ) and the other connected to
the modem for the leased line. The linux box connected to the router has 2
network interfaces, one connected to our campus wide lan, and the other
single interface having two VSNL - assigned IPs. 'ifconfig -a' info is
included.

***** ifconfig -a *****
eth0      Link encap:Ethernet  HWaddr 00:90:27:34:60:09  
          inet addr:202.54.64.101  Bcast:202.54.64.111  Mask:255.255.255.240
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1464331 errors:0 dropped:0 overruns:0 frame:1
          TX packets:1511519 errors:0 dropped:0 overruns:0 carrier:0
          collisions:1375 txqueuelen:100 
          Interrupt:16 Base address:0xfce0 

eth0:0    Link encap:Ethernet  HWaddr 00:90:27:34:60:09  
          inet addr:203.197.138.163  Bcast:203.197.138.191  Mask:255.255.255.224
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:16 Base address:0xfce0 

eth1      Link encap:Ethernet  HWaddr 00:A0:C9:AC:1D:B1  
          inet addr:192.168.1.1  Bcast:192.168.1.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:8879351 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1608197 errors:0 dropped:0 overruns:0 carrier:0
          collisions:38672 txqueuelen:100 
          Interrupt:20 Base address:0xfc20 

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:3924  Metric:1
          RX packets:261049 errors:0 dropped:0 overruns:0 frame:0
          TX packets:261049 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
**** end of ifconfig -a ****

	Now, I suppose we could use one interface for all incoming traffic
like requests for the webpages and incoming mail, while all users browsing
from within our lan, and outgoing mail could use the 512 kbps interface.
How can this be done ? From the routing table on the dual-IP linux box, I
see that it has the 512kbps link as the default route, so all outbound
traffic uses that. But we run a nameserver whose setting have not been
changed. So incoming stuff still comes over the 64 kbps interface. Routing
table below for more info....

202.54.64.101 - linux host IP - old microwave link 64kbps
203.197.138.163 - New 512 kbps link IP for the same linux host
202.54.64.97, 203.197.138.161 - router IP

**** route ****

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.1.1     *               255.255.255.255 UH    0      0        0 eth1
203.197.138.163 *               255.255.255.255 UH    0      0        0 eth0
202.54.64.101   *               255.255.255.255 UH    0      0        0 eth0
202.54.64.96    *               255.255.255.240 U     0      0        0 eth0
203.197.138.160 *               255.255.255.224 U     0      0        0 eth0
192.168.1.0     *               255.255.255.0   U     0      0        0 eth1
127.0.0.0       *               255.0.0.0       U     0      0        0 lo
default         203.197.138.161 0.0.0.0         UG    0      0        0 eth0

**** end of route ****

	Assuming what I have been saying is right, are there any better
ways to use the two links ? or is this idea of using one link for outgoing
and one for incoming traffic the logical one ?

thanks and regards
mani sridhar
<msridhar@xxxxxxxxxxxxxxxx>
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