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How to block bootp/dhcp broadcasting on cisco routers?

 
 
Faustino Dina
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      09-28-2004
Hi,

How can I block bootp/dhcp broadcast at cisco routers?

Thanks in advance

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Faustino Dina
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Ivan Ostreš
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      09-28-2004
In article <(E-Mail Removed)>, http://www.velocityreviews.com/forums/(E-Mail Removed) says...
> Hi,
>
> How can I block bootp/dhcp broadcast at cisco routers?
>


Router is by definition a border of broadcast domain so you don't
actually need to do anything (if you don't have 'ip helper-address' or
'directed broadcast' commands in your config).



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Faustino Dina
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      09-28-2004
> Router is by definition a border of broadcast domain so you don't
> actually need to do anything (if you don't have 'ip helper-address' or
> 'directed broadcast' commands in your config).


Well, that exactly was my assumption. I configured dhcp servers on two
segments of my wan 10.10.10.0/24 and 10.10.34.0/24. But when I connect a
test PC to the 10.10.10.0/24 subnet, it receives the address leased by the
dhcp server at 10.10.34.0/24 'cause it answers first. ANd the address it
leases is a 10.10.34.x one. Then how 10.10.34.0/24 knows of the dhcp request
broadcast. I checked my routers and none of then is configured with 'ip
helper-address' nor 'directed broadcast' commands Even I tryed "no ip
forward-protocol udp bootpc" and "no ip forward-protocol udp bootps" but in
both cases the routers answered there was no port to delete...

What to do?
Thanks for your replay

Faustino


 
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RC
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      09-28-2004
No need to post you problem twice. But a full config would help. And maybe a
description of the physical layout (any chance you have a loop?).

"Faustino Dina" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> > Router is by definition a border of broadcast domain so you don't
> > actually need to do anything (if you don't have 'ip helper-address' or
> > 'directed broadcast' commands in your config).

>
> Well, that exactly was my assumption. I configured dhcp servers on two
> segments of my wan 10.10.10.0/24 and 10.10.34.0/24. But when I connect a
> test PC to the 10.10.10.0/24 subnet, it receives the address leased by the
> dhcp server at 10.10.34.0/24 'cause it answers first. ANd the address it
> leases is a 10.10.34.x one. Then how 10.10.34.0/24 knows of the dhcp

request
> broadcast. I checked my routers and none of then is configured with 'ip
> helper-address' nor 'directed broadcast' commands Even I tryed "no ip
> forward-protocol udp bootpc" and "no ip forward-protocol udp bootps" but

in
> both cases the routers answered there was no port to delete...
>
> What to do?
> Thanks for your replay
>
> Faustino
>
>



 
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Faustino Dina
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      09-28-2004
> No need to post you problem twice. But a full config would help. And maybe
a
> description of the physical layout (any chance you have a loop?).


Thanks, I found what is the problem. These weird subnetworks are connected
to the 10.10.10.0/24 via a wireless shortwave system. The provider
configured this system such a way that the remote pcs can be configured with
10.10.10.x addresses. I think it is similar to have one interface with a
secondary address so there are two logical subnets in the same physical
link. That is why dhcp broadcast from 10.10.10.0 reached the dhcp server at
10.10.34.0/24. I should investigate it later.
Thanks for your attention

Faustino


 
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