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Community Member

NAT-ROUTER

Dear All,

I HAVE cisco 1841.

it has 2 interfaces.

the first one which is f 0/0 is have public ip from my ISP.

the other one is normal, and i am going to give it 192.168.1.100 / 24.

now i have 3 subnets totally diffrent .

i want to create 3 subinterfaces from f0/1.

my question is , how many subinterfaces can i add under the f 0/1 ?

and can i make this Router work as NAT ( overloading ) but all the 4 subnet will use the same public IP Address ?

can it be done as per this diagram ?

please update me.

2 REPLIES
Community Member

Re: NAT-ROUTER

You can issue the "show idb" command (Interface Descriptor Block) to determine how many subinterfaces your router will theoretically support. Each subinterface uses one IDB. Your router should support a few hundred although it may not be recommended to run that many.

As far as overloading for NAT (aka PAT) from multiple inside interfaces you shouldn?t have a problem. Just be aware there is a limit to the number of connections the single outside interface can concurrently support.

Brian Dennis, CCIE #2210 (R&S/ISP-Dial/Security)

bdennis@internetworkexpert.com

Internetwork Expert, Inc.

http://www.InternetworkExpert.com

Toll Free: 877-224-8987

Direct: 775-745-6404 (Outside the US and Canada)

Community Member

Re: NAT-ROUTER

>> show idb <<

Maximum number of IDBs 300

24 SW IDBs allocated (2584 bytes each)

19 HW IDBs allocated (4696 bytes each)

HWIDB#1 1 Ethernet0/0 (HW IFINDEX, Ether)

HWIDB#2 2 Serial0/0 (HW IFINDEX, Frame relay, Serial)

HWIDB#3 3 BRI0/0 (HW IFINDEX, HW ISDN, Serial)

HWIDB#4 4 BRI0/0:1 (HW ISDN, Serial)

HWIDB#5 5 BRI0/0:2 (HW ISDN, Serial)

HWIDB#6 6 Serial1/0 (HW IFINDEX, BSTUN, Serial)

HWIDB#7 7 Serial1/1 (HW IFINDEX, BSTUN, Serial)

HWIDB#8 8 Serial1/2 (HW IFINDEX, Serial)

HWIDB#9 9 Serial1/3 (HW IFINDEX, Serial)

HWIDB#10 10 Dialer1 (HW IFINDEX, HW COMPRESS, Serial)

HWIDB#11 11 Dialer2 (HW IFINDEX, HW COMPRESS, Serial)

HWIDB#12 12 Loopback111 (HW IFINDEX)

HWIDB#13 13 Loopback1111 (HW IFINDEX)

HWIDB#14 14 Loopback1112 (HW IFINDEX)

HWIDB#15 15 Loopback2222 (HW IFINDEX)

====================

yes you can nat all 4 subnets but i ssuppose performance would be affected .

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