TCP Load Balancing, Destination NAT

The "ip nat inside destination" command can be used to split up the load from what looks like one global destination, to several inside hosts. This behaves very much like server load balancing, at least without all the health checks.

Below is the topology. I have static default routes from R1, R2, and R3 pointing to R4. R7 has a static route to each serial link.


Here is R4's config:

interface FastEthernet0/0
ip address 192.168.0.4 255.255.255.0
ip nat inside
ip virtual-reassembly
!
interface Serial1/0
ip address 192.168.45.4 255.255.255.0
ip verify unicast reverse-path
ip nat outside
ip virtual-reassembly
serial restart-delay 0
!
interface Serial1/1
ip address 192.168.46.4 255.255.255.0
ip verify unicast reverse-path
ip nat outside
ip virtual-reassembly
!
ip route 0.0.0.0 0.0.0.0 192.168.45.5
ip route 0.0.0.0 0.0.0.0 192.168.46.6
!
ip nat pool POOL 192.168.0.1 192.168.0.3 prefix-length 24 type rotary
ip nat inside destination list 10 pool POOL
!
access-list 10 permit 192.168.45.10
access-list 10 permit 192.168.46.10

From R7 we will verify:

R7#telnet 192.168.45.10  
Trying 192.168.45.10 ... Open

R1>
R1>exit

[Connection to 192.168.45.10 closed by foreign host]
R7#telnet 192.168.45.10
Trying 192.168.45.10 ... Open

R2>exit

[Connection to 192.168.45.10 closed by foreign host]
R7#telnet 192.168.45.10
Trying 192.168.45.10 ... Open

R3>exit

[Connection to 192.168.45.10 closed by foreign host]
R7#telnet 192.168.46.10
Trying 192.168.46.10 ... Open

R1>exit

[Connection to 192.168.46.10 closed by foreign host]
R7#telnet 192.168.46.10
Trying 192.168.46.10 ... Open

R2>exit

[Connection to 192.168.46.10 closed by foreign host]
R7#

R4's NAT table:

R4#sho ip nat translations
Pro Inside global      Inside local       Outside local      Outside global
tcp 192.168.45.10:23   192.168.0.1:23     200.0.0.7:51519    200.0.0.7:51519
tcp 192.168.46.10:23   192.168.0.1:23     200.0.0.7:64139    200.0.0.7:64139
tcp 192.168.46.10:23   192.168.0.2:23     200.0.0.7:11691    200.0.0.7:11691
tcp 192.168.45.10:23   192.168.0.2:23     200.0.0.7:62913    200.0.0.7:62913
tcp 192.168.45.10:23   192.168.0.3:23     200.0.0.7:17295    200.0.0.7:17295

I used two links just to show the flexibility of this configuration. I was playing around with route-map NAT failover/LB and then decided to work on this scenario.