[nsp] dns forwarding

[Christian Kuhtz]

If you can make that reconfiguration in the DHCP server, why not simply
reconfigure the DHCP server to point to a valid DNS server IP address in the
first place.


On 7/7/04 1:42 PM, "Eric Pylko" <eric at infinitenetworks.us> wrote:

> You're right, but if you set your DNS server to 192.168.0.255 that would be
> a broadcast.  The router _should_ forward that to whatever is configured in
> the ip-helper command.  Whether the DNS server will respond to it is an
> entirely different question.
> 
> Now that I think of it, you might have to do a "no ip directed-broadcast" on
> the interface also to make sure the broadcast gets into the router.
> 
> -Eric
> 
> --
> Eric Pylko   eric at infinitenetworks.us
> CCIE #5827   (585) 747-2446
> 
> 
> -----Original Message-----
> From: Christian Kuhtz [mailto:christian.kuhtz at bellsouth.com]
> Sent: Wednesday, July 07, 2004 1:39 PM
> To: Eric Pylko; 'Kristofer Sigurdsson'; 'Roger'
> Cc: cisco-nsp
> Subject: Re: [nsp] dns forwarding
> 
> 
> Maybe I'm missing something here, but a resolver query to, say, 192.168.0.1
> isn't a broadcast, guys ;).. Forget the ip helper.
> 
> A dedicated NAT/PAT rule is more like it if at all.
> 
> Or using a Dynamic Host Configuration Protocol server for actual dynamic
> configuration ;)... And do away with a hack.
> 
> On 7/7/04 1:30 PM, "Eric Pylko" <eric at infinitenetworks.us> wrote:
> 
>> The ip helper-address command forwards all sorts of broadcasts.  By
> default
>> it does DHCP and a bunch of others (tftp, dns, time (port 37), tacacs,
> bootp
>> client, bootp server, nb name service, and nb datagram service).  These
> are
>> all UDP ports that it forwards.
>> 
>> If you want to disable those (or enable others) you can do with with "no
> ip
>> forward-protocol" or "ip forward-protocol" as needed.
>> 
>> -Eric
>> 
>> --
>> Eric Pylko   eric at infinitenetworks.us
>> CCIE #5827   (585) 747-2446
>> 
>> 
>> -----Original Message-----
>> From: cisco-nsp-bounces at puck.nether.net
>> [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Kristofer
> Sigurdsson
>> Sent: Wednesday, July 07, 2004 1:01 PM
>> To: Roger
>> Cc: cisco-nsp at puck.nether.net
>> Subject: Re: [nsp] dns forwarding
>> 
>> Roger, Wed, Jul 07, 2004 at 11:48:11AM -0500 :
>>> Richard Danielli wrote:
>>> 
>>>> Roger,
>>>> 
>>>> If you only have to satisfy client requests, you might consider looking
>>>> to the ip-helper address command in IOS.
>>>> 
>>>> 
>>> 
>>> Tried that..  Didn't work..  I put the helper address on the internal
>>> interface and pointed the help-address to the dns server.
>>> 
>>> I tried a dns query on the ip of the router and it returned nothing.
>>> From my understanding the helper-address forwards udp broadcasts - ie
>>> for dhcp/bootp a dns query is a udp unicast.
>> 
>> The helper-address directs BOOTP/DHCP IIRC - not broadcasts in general.
> 
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