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NAT solution


I'm looking for some help. I work in nertwork support in an environment where it looks like the IP address scope at some of our sites might not be large enough. From time to time we have large numbers of users come to a site for short periods and the address space is just not large enough to support them. We also don't have enough switch port capacity for when this happens.

At our sites we have WAN routers connected to distribution layer swithches (vlan interfaces and helper addresses defined here) with vlans trunked to access layer switches.

Would it be possible to use a NAT Solution as follows and anyone got any pointers ?

1 -Get a spare router that supports NAT and has two LAN interfaces

2 - Connect  one of the router LAN ints to a spare access switch port and configure that router port as a DHCP client then configure it to be a NAT port (overloading)

3 - Connect the 2nd router LAN Port to another switch which can be used for new clients

Does this make sense ?

as our vlans ints are defined on the 3750 distribution layer which doesn't support NAT, I figure I'm going to have to introduce a router to do the NAT'ing

Any ideas ?


Re: NAT solution


I don't see any problem including the spare router to do NAT and save some IP space.

It's hard to give you any recommendations without more understanding of your topology.

Could you be more specific in your question and we'll try to help you out with this.


New Member

Re: NAT solution

Hi Federico,

Many apologies for the delay in responding. I’ve included a diagram to show what I mean.

During major incidents when some of our sites get overrun with users i.e lots of people turn up at smaller sites ,we want to be able to to provide additional switch port capacity and NAT due to limited port capacity and address space. We want a solution whereby a non Cisco person could just plug in a 2621XM router to an existing access port and hang a switch off it.

My idea is that Fa0/0 gets a dhcp address in the vlan e.g vlan104 in this case and then we configure NAT so that additional users plugged into the temporary switch get an address that is translated to the address on Fa0/0.

Does this solution make sense and sound feasible ? I’m not sure how I would configure this and am looking for some ideas. Any suggestions much appreciated ?



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