[c-nsp] Leakage with NAT Access list

[Imad Buhidma]

Hello

We have Weird problem with NAT on CISCO 7200 router, There's  leakage with NAT access list, The nat translation table shows some denied ip addresses can do successful nat . 

The output of "show ip nat translations" command :

Pro   Inside global           Inside local          Outside local         Outside global
icmp  xx.xx.61.2:0          64.0.96.42:0          201.19.11.100:0       201.19.11.100:0
icmp  xx.xx.61.2:0          64.0.96.42:0          203.59.89.117:0       203.59.89.117:0
icmp  xx.xx.61.2:0          64.0.96.42:0          204.96.151.138:0      204.96.151.138:0
icmp  xx.xx.61.2:0          64.0.96.42:0          213.10.113.206:0      213.10.113.206:0
tcp   xx.xx.61.2:113        64.0.96.42:113        134.181.128.1:33639   134.181.128.1:33639
tcp   xx.xx.61.2:113        64.0.96.42:113        209.139.92.14:64944   209.139.92.14:64944
tcp   xx.xx.61.2:139        64.0.96.42:139        xx.xx.185.108:4865    xx.xx.185.108:4865
tcp   xx.xx.61.2:445        64.0.96.42:445        xx.xx.191.202:2823    xx.xx.191.202:2823
udp   xx.xx.61.2:1032       64.0.96.42:1032       64.4.12.201:7001      64.4.12.201:7001
tcp   xx.xx.61.8:135        64.132.47.202:135     xx.xx.186.156:1530    xx.xx.186.156:1530
tcp   xx.xx.61.8:445        64.132.47.202:445     xx.xx.52.12:3102      xx.xx.52.12:3102
udp   xx.xx.61.7:1434       217.139.226.243:1434  222.174.115.18:1032   222.174.115.18:1032
tcp   xx.xx.61.7:3128       217.139.226.243:3128  59.188.4.140:60257    59.188.4.140:60257
tcp   xx.xx.61.2:1100       172.16.16.216:1902    69.90.63.96:80        69.90.63.96:80
tcp   xx.xx.61.2:1174       172.16.16.216:1903    67.15.14.45:80        67.15.14.45:80
udp   xx.xx.61.2:1904       172.16.16.216:1904    xx.xx.42.2:53         xx.xx.42.2:53
udp   xx.xx.61.2:1905       172.16.16.216:1905    xx.xx.42.2:53         xx.xx.42.2:53
tcp   xx.xx.61.2:2464       172.16.16.205:2464    204.127.202.26:25     204.127.202.26:25
tcp   xx.xx.61.2:2465       172.16.16.205:2465    66.148.71.105:8712    66.148.71.105:8712

We permit only 172.16.0.0/16 network but we have other ip addresses in nat translations like  64.0.96.42 , 64.132.47.202 and 217.139.226.243

Here is the configuration of the router which is running IOS c7200-js-mz.123-8.T3


aaa new-model
!
aaa authentication ppp default group radius local
aaa authorization network default group radius local
aaa accounting network default start-stop group radius
aaa session-id unique
ip subnet-zero
!
bba-group pppoe PRIVATE_IP
virtual-template 1
!
interface GigabitEthernet0/1
bandwidth 100000
ip address x.x.x.x x.x.x.x
ip nat outside
ip virtual-reassembly
ip route-cache flow
duplex auto
speed auto
media-type rj45
no negotiation auto
no keepalive
no cdp enable
!
interface ATM1/0
no ip address
no atm ilmi-keepalive
!
interface ATM1/0.1 multipoint
range pvc 10/35 10/135
  protocol pppoe group PRIVATE_IP
!
range pvc 12/35 12/135
  protocol pppoe group PRIVATE_IP
!
range pvc 13/35 13/135
  protocol pppoe group PRIVATE_IP
!
!
interface Virtual-Template1
ip unnumbered GigabitEthernet0/1
ip access-group 112 in
ip mtu 1492
ip nat inside
ip virtual-reassembly
peer ip address forced
peer default ip address pool PRIVATE_IP_POOL
ppp authentication pap chap
!
ip local pool PRIVATE_IP_POOL 172.16.0.1 172.16.255.254
!
ip nat pool NAT_POOL xx.xx.61.1 xx.xx.61.254 netmask 255.255.255.0
ip nat inside source list 111 pool NAT_POOL overload
!
access-list 111 permit ip 172.16.0.0 0.0.255.255 any
access-list 111 deny   ip any any
access-list 112 deny   ip any 192.168.0.0 0.0.255.255
access-list 112 deny   ip any 172.16.0.0 0.15.255.255
access-list 112 deny   ip any 10.0.0.0 0.255.255.255
access-list 112 permit ip 172.16.0.0 0.0.255.255 any
access-list 112 deny   ip any any


Can anyone explain what's happening?