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Cisco 1841 ethernet ports as a switch

By neghvar ·
I need to configure to ethernet ports on a router to function as a hub or switch. no actual routing, no subnet change.
our layout is LAN-->Switch-->Firebox 750e-->cisco 2811-->T1

I need to stick our cisco 1841 between the firebox and switch. It's only purpose is for Netflow and I need f0/0 & f0/1 to act like switch ports, not router ports.

Any clues?

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using router as switch

by teaml8ians In reply to Cisco 1841 ethernet ports ...

Yes we can use router as switch.
By disabling dhcp & nat we can use it as a switch.
u can connect fo/0 to switch and f0/1 to the firebox 750e.

by default in new router,all the services will be disable.

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just disabling DHCP and NAT? how about default route

by BizIntelligence In reply to using router as switch

Switch is layer 2 device (except some switches which are layer 3) and Router is layer 3 device. That means switch forward <b>frames</b> based on mac-address table and router forward <b>packets</b> based on IP routing table. We can't really make router to forward <b>packets</b> based on mac-address table.

I have not done it before but I believe despite disabling all the router features you will need to add default routes i.e.

ip route 0.0.0.0 0.0.0.0 FA0/0
ip route 0.0.0.0 0.0.0.0 FA0/1

and then connect router between switch and firebox. In that case, router will forward each packet coming in and going out without worrying about it destination or source.

Please note I have not done it before practically but I did that in Cisco Packet Tracer 5.1 and it worked. You should also try it in simulator before you do it in real life.

Also if you find anything to make router as switch then please let me know. I would love to learn that.

Good Luck !

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Layer 3 feature

by neghvar In reply to Cisco 1841 ethernet ports ...

I forgot to mention that the purpose of this device is for the Netflow feature in the router. A friend of mine stated bridging the two ports but that it may negate the layer-3 features like Netflow & IP SLA which we need. We are also planning to implement SolarWinds's Orion NPM and Netflow analyzer.

I forgot about packet tracer. I used it in a CCNA course I took at a local college. I'll try that, but I doubt it will have the features I need.

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