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As an IOS neophyte, I've been struggling to configure our office's new Cisco 887VAW ADSL router. After much head-scratching I've managed to sort the ADSL end out, and configured the router to provide DHCP on its ethernet interface (192.16.10.0/24, with the router on 192.168.10.1, NATing to the ISP-supplied IP address).

Now I need to configure the router to forward traffic for the /29 subnet we've got from our ISP. The previous router was configured with a second IP address (from the /29) which is specified as the outbound gateway for our various servers; how do I replicate this on the Cisco, and tell it how to route inbound data for those addresses?

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You should be able to configure the /29 exactly the same as your /24 if they're sharing the same Layer 2 (switches etc) network inside your network? –  fukawi2 Feb 26 '13 at 23:13

1 Answer 1

up vote 1 down vote accepted

If you're running a flat network internally (no vlans on the 4 LAN ports) you can just add the ISP assigned address as a secondary:

int vlan 1
ip address x.x.x.x 255.255.255.248 secondary

If you are running vlans internally you need to define a new vlan, add the address to that interface and assign LAN ports to that vlan:

vlan 2
 name ISP_Assigned

int vlan 2
 description ISP Assigned Space
 ip add x.x.x.x 255.255.255.248
 no shut

int fa0/x
 description Switchport Assigned to ISP IP Space
 switchport access vlan 2
 no shut
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secondary was the keyword I was missing, thanks :) –  Andy S Feb 27 '13 at 10:12

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