[c-nsp] IOS NAT, translating source into IP not included in routing table

[Dale Shaw]

Hi,

My Google-fu is failing me..

Scenario:

FastEthernet0 (NAT inside), IP 10.20.20.1/24
Tunnel1 (NAT outside), IP 172.16.0.1/24
DMVPN environment with EIGRP
Performing static source address translation from hosts in
10.20.20.0/24 to 192.168.20.x

interface FastEthernet0
 ip address 10.20.20.1 255.255.255.0
 ip nat inside
 no ip redirects
 no ip proxy-arp
!
interface Tunnel1
 ip address 172.16.0.1 255.255.255.0
 ip nat outside
 no ip redirects
 no ip proxy-arp
!
interface Loopback0
 ip address 10.63.6.100 255.255.255.255
!
router eigrp 10
 redistribute static
 passive-interface default
 no passive-interface Tunnel1
 network 10.63.6.0 0.0.0.255
 network 172.16.0.0 0.0.0.255
 no auto-summary
!
ip nat inside source static 10.20.20.50 192.168.20.5
ip nat inside source static 10.20.20.51 192.168.20.6
ip nat inside source static 10.20.20.52 192.168.20.7
ip nat inside source static 10.20.20.53 192.168.20.8
[...] etc etc

The router will happily translate 10.20.20.50 etc. into any arbitrary
IP, as per the "ip nat inside .." command, but return traffic is
unrouteable because there is no routing table entry for 192.168.20.5
in other routers in the AS.

At present, I'm adding and redistributing a static host route like so:

ip route 192.168.20.5 255.255.255.255 FastEthernet0 10.20.20.2

..And as expected, 192.168.20.5/32 appears in the routing table and
packets know how to come back to this router.

It's a bit ugly/counter-intuitive though, don't you think? Is there a
more elegant way? (perhaps specifying Null0 in the static route would
be nicer)
I have a mix of 12.3 and 12.4 IOS in the environment so while I'm
happy to hear about any better methods, ideally I'm looking for
something that will work on all versions.

cheers,
Dale