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Cisco 871 Routers

Answered Question
Nov 11th, 2014
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Hi Guys,

This series of routers has a built in switch. I understand that to enable routing the switch ports must become part of a configured vlan on fe0,fe1,fe2 and fe3. Fe4 does not have a layer 2 port and is layer 3 only. On the device fe4 is clearly labelled 'WAN'. My question is, to enable routing from the LAN out to the WAN, must I create a virtual connection from the vlan to fe4? Would this involve configuring the dot1q protocol on fe4 or possibly a trunking command? If this were a seperate physical router and switch, all I would need to do is plug the switch in to the router with a physical cable. I guess I need to work out how to do this virtually.

Thanks :)

Correct Answer by John Blakley about 2 years 9 months ago

I'm not sure I understand your question. The vlan interface on the router will have the lan side address. The WAN interface will either have a statically assigned public address or it will get an address from dhcp from your provider (if you're connecting it directly to the ISP). The only thing that you would really have to configure outside of that is going to be your default gateway and nat. You don't have to configure encapsulation on FE4.

Think of it this way. Your vlan interface on the router is effectively bridging all of the switchports on the router. Any port that you connect to will be part of vlan 1. VLAN 1's ip address becomes the default gateway for the devices connected to it.

HTH,

John

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Correct Answer
John Blakley Wed, 11/12/2014 - 03:01
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I'm not sure I understand your question. The vlan interface on the router will have the lan side address. The WAN interface will either have a statically assigned public address or it will get an address from dhcp from your provider (if you're connecting it directly to the ISP). The only thing that you would really have to configure outside of that is going to be your default gateway and nat. You don't have to configure encapsulation on FE4.

Think of it this way. Your vlan interface on the router is effectively bridging all of the switchports on the router. Any port that you connect to will be part of vlan 1. VLAN 1's ip address becomes the default gateway for the devices connected to it.

HTH,

John

Paul Smith Wed, 11/12/2014 - 03:34
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Thanks for clarifying. Looks like I was way over-analyzing. :)

 

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