Changing a live "ip local pool": will it disrupt the existing vpdn connections?

[LondonCisco]

Hi All

We have VPDNs which allows our clients' ADSL routers to connect to our core infrastructure.

We control the LNS routers whereas a supplier controls the LAC routers.

Our current ip local pool configuration on the LNS routers is as follows:

ip local pool <pool name> X.X.6.1 X.X.7.254

However, I would like to remove some ip addresses from this range. My understanding, is that the "no ip local pool <pool name> X.X.X.X Y.Y.Y.Y" only removes complete ranges within the pool, not part of an existing range. Therefore, I think my configuration solution is:

config t

no ip local pool <pool name> X.X.6.1 X.X.7.254

ip local pool <pool name> X.X.6.1 X.X.6.63

ip local pool <pool name> X.X.6.128 X.X.6.254

ip local pool <pool name> X.X.7.1 X.X.7.254

exit

i.e. I'm removing X.X.6.64-X.X.6.127 from the pool.

My question is this:

There will definitely be live connections in the "X.X.7.1-254" range and the "X.X.6.128-X.X.6.254" range. Will they be disconnected by this configuration change and be forced to reconnect or will they stay connected as the ip addresses exist both in the original and new configuration?

Many Thanks!

John

[mbilgrav]

To my observation, what you are trying to accomplish can be done in an other way:

"ip dhcp excluded-address X.X.6.64 X.X.6.127"

This is nondisruptive.

HTH

Martin

[mbilgrav]

In accordance with DHCP standard, clients obtained an IP will release/renew after half the lease time.

Hence if you change DHCP server settings your clients will not disconnect at that moment ...

[LondonCisco]

Hi Martin

The "excluded-address" option didn't appear to apply to "ip local pool ".

I reconfigured as per my original post:

config t

no ip local pool X.X.6.1 X.X.7.254

ip local pool X.X.6.1 X.X.6.63

ip local pool X.X.6.128 X.X.6.254

ip local pool X.X.7.1 X.X.7.254

exit

I found none of the existing vpdn connections using the ip local pool were dropped.

John

[mbilgrav]

Hello,

I am glad that you got your answer. Please mark the question as answered.

The exclude-command is a global command.

[LondonCisco]

Hi Martin

I don't understand what you mean about the exclude command being global in this context.

I understand that you were able to use it in the following context:

"ip dhcp excluded-address X.X.6.64 X.X.6.127" i.e. with "ip dhcp".

I wanted to exclude addresses from "ip local pool"

However, when I tried the following:

>no ip local pool ?

It returned the following options:

A.B.C.D First IP address of range

i.e. "excluded-address" wasn't one of them!

John

[mbilgrav]

that is right !

global mean that you just type it in, hence NOT under any other commands, like "ip local pool ?"

simply login to your router and type conf t, then type "ip dhcp exclude?"

router(config)#ip dhcp excluded-address ?

  A.B.C.D  Low IP address

This is the way to exclude IP addresses from a scope in a IOS router.

But maybe you are not using a router ?

8-)

[LondonCisco]

Hi Martin

Maybe I'm being a bit slow here! But I still don't understand.

I am using a router.

The "ip dhcp excluded-address ?" does work as you say on the router. However, I'm trying to exclude the ip address from "ip local pool ?".

Are these the same then - I had assumed that they were different? We are using the "ip local pool " for addresses for vpdn - I had assumed that this would be different to the addresses for dhcp.

John

[mbilgrav · Accepted solution]

ahh - I think I am the slow part here then ...

VPDN/LNS will use "local" and not "dhcp" - to that you are right.

so maybe address exclussion can be done otherwise with "ip local pool", or maybe the solution you have made is the only way.

but that doesnt change the fact that dhcp client will not disconnect as result of changing the DHCP-server.

Sorry If I mislead you.

[LondonCisco]

No problem. The picture is clear now. Thanks for your time.