Please help !! static IP assignment in DSL (IP-DSLAM)

Unanswered Question
Jun 6th, 2007

can someone please explain me how can I assign a DSL user static ip address ? We are using IP DSLAM not ATM. There are many users who wants a static ip address, so I need the example how can I assign it to them. Let`s say I give them the ip and this ip must be fixed, which means that user must not be able to use other ip than this one ! he must not be able to use or other...... I was told to use static arp table, but this can`t work.

And we are NOT talking about ATM in this case but the IP-DSLAM and VLANS. The other option I was told is to assign the subnet /30 but I can`t do this either, because in this case I am giving the user 2 static ip addresses instead of only one.

The interface example config from BRAS:

int fa0/0.20

description DSL_customers

encapsulation dot1Q 20

ip address

so we configure the IP DSLAM that all ports are assigned to VLAN 20 and users now can use ALL awailable ip addresses from this subnet if I can`t deny it to them, therfore I need an example how to fix this ?

Any great suggestions???

I have this problem too.
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dgahm Wed, 06/06/2007 - 12:35

The /30 would only allow one address to be used by the customer. Your interface would use the other address.

Please rate helpful posts.


050878james Wed, 06/06/2007 - 12:40

Thank You very much for reply !

Hmm, but is this really done on this way ?? any way ? I mean is this the only solution ?


050878james Wed, 06/06/2007 - 12:47

I know about one ISP here that gives the static ip addresses to dsl customers, but all of these customers have the same gateway, so it can`t be possible that /30 is solution any way ?? what you suggest ??

In case of block /30 on the interfaces, each user should than have different gateway, but I am not really sure is this right solution.

As you sure know if I should use /30 than the interface ip address should be the dsl users gateway, so each user should than have different gateway.


dgahm Wed, 06/06/2007 - 12:50

Why can't you configure static ARP entries?

050878james Wed, 06/06/2007 - 12:53

Because the static ARP will not deny user to TRY just use another ip address from the subnet as well ??.. if that ip is not in use.

do You have any example about it ?? You could provide me ?? just short example config ?

050878james Wed, 06/06/2007 - 13:02

could You please provide me an example how the config should look like than ? in case static arp ?

You can use the interface as example below:

int fa0/0.20

description DSL_customers

encapsulation dot1Q 20

ip address

so........ static arp ?.. it should be binded to IP-DSLAM switch port I think ? because if the user change the modem than he will not be able to access the internet if the static arp works as You say.

050878james Thu, 06/07/2007 - 00:49

I was thinking about block /30 but any way we will lose 1 ip.

One needs to be used for VLAN sub-interface and another is used by user, so actually there is 2 ip address for 1 dsl user and if we are taliking about 25 000 dsl users, than we will loose many ip addresses because we need 50 000 ip addresses for 25 000 customers.

tahequivoice Thu, 06/07/2007 - 09:58

Have you considered using Radius and PPPOE? That would be the easiest solution to assigning IP addresses to customers. Basically you setup in radius the IP or subnet of IP's that would be assigned to the customer, then when they log into the network using PPPOE the IP will be assigned to them. You will need to use a routing protocol such as EIGRP or OSPF for this, and terminate the client onto a pppoe server such as a cisco router like a 2600 or 3600 series, or 2800 series if you can afford it. For the radius server, you can use open source on a linux box, and all XP machines have a built in pppoe client, and most, if not all soho routers now support PPPOE. You can even get fancy with radius and rate limit users for bandwidth reasons. You can gain better control over customers, so if one fails to pay their bill, you can disable their account and kick them without having to go to the dslam and disconnect the physical wires. It has been quite a while since I have worked with DSL, but it is doable.

050878james Thu, 06/07/2007 - 10:17

Hello dude !!

First of all THANK YOU very much for reply.

I was thinking about PPPoE, but the static ip address assigment right from BRAS impressed me from one ISP near us.

They just give the users static ip address and they configure it in the router and nothing more they are on the internet.

But what most impressed me is when they give the ip address to one user he is able to use only that ip address and no other. So it must be binded on one or another way, but how ? :(

I will try everything absolute everything before I decide to use the PPPoE.

Hope You have a solution

Thank You again !!

Best regards


pooria_koleyni Sat, 07/21/2007 - 07:24

Hi ,Static IP assignment using radius is exactly what i am looking for . i have some customers that connect using ADSL and use PPPoE

I wan to assign them for example /29 ip address

Their CPEs are router . .so when then connect to my router i think radius should put static route on my router


Do u have any configuration template that shows how we can assign for example /29 static ip to ADSL user ?

050878james Sat, 07/21/2007 - 13:50

static ip address assigment using PPPoE is possible, but it is not done on the way you want to do so, when assigning static ip address to dsl customer using radius server, than assign only ONE static ip address, it is nothing but just tell the RADIUS that this (specified) pppoe account MUST allways get that (specified) ip address. So when this is done, this customer have allways the same static wan ip address when he connects to the internet. Than if this user need more than only one static ip address for example /29 as you asked for, than on the BRAS (router) just configure a static ip route which will route the subnet /29 TO THE customer static ip address you gave him on the radius server.

Hope you understand, this was an explanation how static ip address assigment via radius server is working. It is not usually to give the users subnet such as /29 via radius, via radius server you only give ONE static ip address to that dsl customer, THAN you create the static ip route on the BRAS which routes the subnet /29 to users static ip address you gave him on the radius server.

So another question you asked for is HOW TO DO IT ON the RADIUS server, this is little difficult for me to explain, because it depends where you are running RADIUS server, is it on Windows ?? LINUX etc.....

but any way it is not difficult, we used Windows RADIUS server.

Hope this helps...

Best regards

pooria_koleyni Mon, 07/30/2007 - 03:59

I found the way and it is possible

radius can put static route one or more on the router for the customer that connect using PPPoE


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