by Alysa » 25 Oct 2012, 19:53
Buy a Cisco PIX with multiple WAN ports and it will load balance for your.
Or
With a cisco 3700 router and a 2950 port switch I have been able to NAT LAN connections to 4 cable modems. Plug your cable modems in the 2950 ports and put each one on a diffrent VLAN, create an ISL or Dot1Q trunk from the switch to the router. Create virtual sub interfaces on the link from the switch and apply each sub interface one of the VLANS from the switch. So if you have 3 cable modems put them on VLAN 10, 20, 30. Then trunk VLAN 10, 20, 30 to the router and create FastEthernet0/0.10, FastEthernet0/0.20, FastEthernet0/0.30. For each subinterface have them aquire their IP address via DHCP. Apply an "ip nat outside" to each subinterface. For the inside interface apply and ip nat inside. Build access-lists consisting of the machines you want on each cable modem. So build:
access-list 110 permit ip host x.x.x.x
access-list 120 permit ip host x.x.x.x
access-list 130 permit ip host x.x.x.x
You can put multiple ip address or subnets on each access list. Finally build you global nat statement.
ip nat source-list 110 interface fastEthernet0/0.10 overload
ip nat source-list 120 interface fastEthernet0/0.20 overload
ip nat source-list 130 interface fastEthernet0/0.30 overload
So every host in access list 110 will go out to VLAN 10 on the outside switch which will then put the information on that cable modem.
This is a clunky way to do NAT and it's not really load balancing I would just research a cisco PIX