Please follow the below guide to securely terminate a fiber (FTTP) broadband service on a Cisco C1117-4P router.
This configuration will handle DHCP on the LAN , outbound NAT (dynamic PAT), and statefully inspect packets to ensure connections are only ever built outbound.
The router will be unreachable from the outside world and can only be managed internally from the LAN via SSH, or locally via console.
This guide assumes a basic working knowledge of configuring Cisco equipment with a console cable.
Prerequisites
Please populate the below, ready to merge into the main config.
Enable password = #ENABLE_PASSWORD#
Login username = #USERNAME#
Login password = #PASSWORD#
Console and VTY fallback password = #FALLBACKPASSWORD#
Broadband username = #BROADBAND_USERNAME#
Broadband password = #BROADBAND_PASSWORD#
Configuration Steps
1 – Ensure any existing config on the router has been wiped and you are starting from fresh. (write erase & reload).
An enable secret is required following the first boot. Enter your enable password below.
The following will now be displayed:
As we don’t want to save anything at this stage, I would enter 0 when prompted. This should allow us to start with a blank config.
Finally, if prompted to enter the initial config, type ‘no’.
2 – Enter global configuration mode and apply general ‘best practice’ fixups
service sequence-numbers
service timestamps debug datetime msec localtime show-timezone
service timestamps log datetime msec localtime show-timezone
service tcp-keepalives-in
service tcp-keepalives-out
service password-encryption
logging buffered 10240000
login on-success log
login on-failure log
clock timezone GMT 0 0
clock summer-time BST recurring last Sun Mar 1:00 last Sun Oct 1:00
no ip http server
no ip http secure-server
no ip http authentication local
ntp server 134.226.81.3
hostname R1
3 – Define login credentials and secure remote access
! Login credentials
enable secret 0 #ENABLE_PASSWORD#
username #USERNAME# privilege 15 secret 0 #PASSWORD#
ip domain name cisco.router
crypto key generate rsa general-keys modulus 4096
! Secure console and VTY lines
ip access-list standard SECURE_VTY
10 permit 192.168.1.0 0.0.0.255
exit
line con 0
password #FALLBACKPASSWORD#
login local
session-timeout 15
exit
line vty 0 15
password #FALLBACKPASSWORD#
login local
transport input ssh
access-class SECURE_VTY in
session-timeout 15
exit
4 – Configure Zones and ACLs to support stateful packet inspection
! Configure Zones
zone security OUTSIDE
zone security INSIDE
exit
! Configure ACLs to match traffic.
ip access-list extended ACL_ZBFW_INSIDE_TO_OUTSIDE
10 permit ip any any
exit
ip access-list extended ACL_ZBFW_ROUTER_TO_OUTSIDE
10 permit ip any any
exit
! Configure class-maps to match ACLs.
class-map type inspect match-any CM_ZBFW_INSIDE_TO_OUTSIDE
match access-group name ACL_ZBFW_INSIDE_TO_OUTSIDE
exit
class-map type inspect match-any CM_ZBFW_ROUTER_TO_OUTSIDE
match access-group name ACL_ZBFW_ROUTER_TO_OUTSIDE
exit
! Configure policy maps to reference class maps.
policy-map type inspect PM_ZBFW_ROUTER_TO_OUTSIDE
class type inspect CM_ZBFW_ROUTER_TO_OUTSIDE
inspect
class class-default
exit
exit
policy-map type inspect PM_ZBFW_INSIDE_TO_OUTSIDE
class type inspect CM_ZBFW_INSIDE_TO_OUTSIDE
inspect
class class-default
exit
exit
! Configure Zone pairs to reference policy-maps.
zone-pair security INSIDE_TO_OUTSIDE source INSIDE destination OUTSIDE
service-policy type inspect PM_ZBFW_INSIDE_TO_OUTSIDE
zone-pair security ROUTER_TO_OUTSIDE source self destination OUTSIDE
service-policy type inspect PM_ZBFW_ROUTER_TO_OUTSIDE
5 – Configure LAN interface and enable DHCP
! Configure VLAN 1 interface and DHCP
interface Vlan1
description ### LAN DEFAULT GATEWAY ###
ip address 192.168.1.254 255.255.255.0
ip nat inside
zone-member security INSIDE
no shutdown
exit
ip dhcp excluded-address 192.168.1.0 192.168.1.10
ip dhcp excluded-address 192.168.1.240 192.168.1.254
ip dhcp pool VLAN_1
network 192.168.1.0 255.255.255.0
default-router 192.168.1.254
dns-server 1.1.1.1 8.8.8.8
exit
! Configure built-in switchports
interface range gi0/1/0-3
description ### ACCESS PORT ###
switchport
switchport mode access
switchport access vlan 1
spanning-tree portfast
no shutdown
exit
6 – Configure PPPoE interface
interface GigabitEthernet0/0/0
description ### PPPoE INTERFACE – TO ISP FIBER MODEM ###
no ip address
negotiation auto
pppoe enable
pppoe-client dial-pool-number 1
no cdp enable
no shutdown
exit
7 – Configure Dialer interface and default route
! Dialer interface
interface Dialer1
description ### OUTSIDE INTERFACE ###
mtu 1492
ip address negotiated
no ip redirects
no ip unreachables
ip nat outside
zone-member security OUTSIDE
encapsulation ppp
ip tcp adjust-mss 1452
dialer pool 1
dialer-group 1
no cdp enable
ppp authentication chap callin
ppp chap hostname #BROADBAND_USERNAME#
ppp chap password 0 #BROADBAND_PASSWORD#
ppp ipcp route default
ppp ipcp address accept
no shutdown
exit
! Default route
ip route 0.0.0.0 0.0.0.0 dialer1 name DEFAULT_VIA_VDSL
8 – Configure outbound NAT (Dynamic PAT)
! NAT ACL
ip access-list extended NAT
permit ip 192.168.1.0 0.0.0.255 any
exit
! NAT Rule
ip nat inside source list NAT interface dialer1 overload
end
9 – Verify the configuration works
! Confirm ISP has assigned an IP address to the router.
show ip int brief
! Test a ping to Google
ping 8.8.8.8
10 – Verify and save the configuration
! Verify running-config and ensure all of the above commands have been applied.
show run
! Save running-config to NVRAM
copy running-config startup-config
– or
wr
11 – Conclusion
You should now have a working broadband connection with a router that has been secured for local management.
At this point it should be possible to connect your laptop to the router switchports and open an SSH session to 192.168.1.254, logging in with the username and password configured earlier.
(The fallback password will only ever be used in the event the local username is removed in error).
The ZBFW configuration is very basic, if you intend to configure site-site VPNs you will likely need to add an OUTSIDE -> Self zone with bespoke rules to permit inbound connectivity from the remote peer. A policy-map can be configured to either ‘inspect’ or ‘pass’ packets, I have found ‘pass’ for protocols such as IKE/ESP can prevent common problems.
For convenience, please find copy of running-config below: