How should I configure my Motorola SBG6580 for use with a Cisco router/switch (model #'s inside)

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JoshJ5Hawk

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Oct 23, 2013
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Hey guys, double ended question here. I got a killer deal at work on a Cisco 2821 ISR a Cisco 2950 24 port switch (Layer 2) ($60 for the pair).

I currently have the setup *working* but I feel it's not quite right. I still have my SBG6580 (Cable Modem) in router mode, because if I flip it over to bridge mode, I lose everything. I have NAT setup on my Cisco Router, as well as a DHCP server. When I do have the setup deployed (currently not using it, as I'm working to get it in a location that isn't my bedroom floor) everything works perfectly fine (included using the DHCP pool on the 2821, somehow. Because from my limited knowledge, double NAT and double DHCP is a very bad thing.

The next question is how do I go about port forwarding with my 2821, instead of my surfboard. The main reason I *am* choosing to use the 2821 instead of just popping the switch on the network, is well, it's more fun (and from what I've read, using a single command to set up the Port Forwarding is faster/easier that screwing with the SBG6580)! I have seen some information about port forwarding around, but I figure since I'm asking the one question, I might as well throw both in.

Thank you all for your time
 
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You generally do not have static ip unless you pay for them. It would then depend how the ISP allocates it to you.

Not sure what you mean g0/0 can be either the lan or the wan....or actually both if you get very creative. The DHCP pool is not mapped to a port it is done by matching ip blocks. A router can act as a DHCP server for many interfaces and even networks that are not directly connected to the router.

Now if you mean the ip address dhcp command that would go on a WAN port that you get dynamic ip from the ISP.
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bill001g

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Aug 9, 2012
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You should have no issue running it in bridge mode the router does not know. Try to plug your pc into the modem in bridge mode and make sure that works. It is tricky sometime because the modem only allows the first mac address on the lan port to get a IP. You most times must condigure the modem to bridge/modem mode and save the config and the reboot the device. Whatever you plug in first gets the ip. You can set a fixed mac address if you need to.

There are lots of debug commands to see if the router is being offered a ip on the port you have connected to the modem.

Port forwarding is done with a static nat command you put in addition to main one that you put in to get the default. Make sure you map it to the interface just like the main nat command. It looks strange but when you are getting your ips on you outside interface via dhcp you only do not know the ip.
 
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B

bill001g

Titan
Aug 9, 2012
28,324
2,755
125,640
You generally do not have static ip unless you pay for them. It would then depend how the ISP allocates it to you.

Not sure what you mean g0/0 can be either the lan or the wan....or actually both if you get very creative. The DHCP pool is not mapped to a port it is done by matching ip blocks. A router can act as a DHCP server for many interfaces and even networks that are not directly connected to the router.

Now if you mean the ip address dhcp command that would go on a WAN port that you get dynamic ip from the ISP.
 
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JoshJ5Hawk

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Oct 23, 2013
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10,510


Thanks exactly what I meant :) and why I couldn't figure it out at 3 am haha. thanks again!

edit: and for clarification I did mean non-static ip lol
 
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