Cisco 2600, Fractional T1 and DHCP

Posted on 2003-11-17
Last Modified: 2010-04-17
Hi all.

I would like to know if it's possible to use a fractional T1 512kb with 20 users?
Would I be able to configure the Cisco router to run DHCP?
Using a Cisco 2600

Since we can't afford to have a real network all my users need is access to the internet.

Would anybody be able to point me to an example configuration?

I am sure the router can also be a low grade firewall as well?
I am assuming with the latest IOS
Question by:ShinCat
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LVL 79

Expert Comment

ID: 9766163
Sure it can.
Assuming that you have enough memory in it to run the "PLUS" feature set, and that you have an integrated WIC T1 DSU module.

Pretty basic config:

Interface serial 0/0
 no shutdown
 description Link to Internet Circuit ID ZZ989L43C  <-- descriptive text
 ip address  <-- provided by ISP
 encap frame-relay | ppp  <-- ISP tells you which
 ip nat outside  <-- firewall at most basic level - network address translation
Interface Ethernet 0/0
 no shutdown
 ip address  <-- use private IP addresses
 ip nat inside  <-- inside private ip addresses are translated to the one public IP
ip nat inside source list 1 interface serial0/0 overload
access-list 1 permit
! setup the DHCP server piece
! ip dhcp pool {name}
ip dhcp pool dhcppool1
 domain name
 dns-server  <-- local dns server and failsafe public dns server
 netbios-name-server  <-- local WINS server (if you have one)

Badabing..... that's about all there is to a basic config.
There are several things you'll want to add to "lock it down" a little more. Best place to start is to look at the securing Cisco edge router guides at

Author Comment

ID: 9767798
Funky fresh!

You win the prize!

How much memory would you say for 20 people?

32MB do the trick?

Or like anything else the more memory the merry? :)

hmm the DNS server may be tricky. Since we don't have a real network, just users with machines.
maybe a Linux DNS server would work?
LVL 79

Accepted Solution

lrmoore earned 250 total points
ID: 9767890
Anything you can setup as an internal DNS will help...

You'll need the "T" train of IP PLUS IOS
If you go with 12.3, you'll want 64Mb DRAM and 16M flash on your 2600
Cheap DRAM from
As always, more than the required minimum is better
That'll also give you the option to run the Firewall feature set in the future (although for the money, I prefer a 'real' firewall like the PIX)
With this setup, you'll have no problem for 20 - 50 people..
Although I would highly suggest looking at a PIX firewall as soon as budget allows.
The 506e would be my recommendation. For around $1000 you can't go wrong.
Gives you intrusion detection, stateful packet inspection, application layer packet inspection, and VPN capabilities.

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