An "IP directed broadcast" means a broadcast to a specific network or
subnet, for example 172.16.255.255 or 172.16.10.255. It's a generic
concept, not specific to DHCP.
You can have the forwarded DHCP UDP packets go to a directed broadcast
instead of to a specific address. In the ip helper-address command, you
could say 172.16.255.255 instead of 172.16.1.1, for example. This might be
useful if you had multiple servers, or for some reason didn't know the
exact address of the server.
Newer versions of Cisco IOS include the command "no ip directed broadcast"
by default. This is to stop hackers from sending packets to directed
broadcast addresses. I don't know what would happen if you had this command
but you also used a directed broadcast in the ip helper-address command.
Priscilla
At 02:40 PM 9/26/01, you wrote:
>Thanks Priscilla,
>I've been looking for that command on Cisco's web site and I could not
>find its description. Disabling udp broadcasts on port 137 and 138 solved
>the problem. So I think that I am going to stick to it. If you do not
>mind would you please explain what ip directed broadcast does and how it
>affects ip helper and udp broadcast. I was not able to find a clear
>explanation for this.
>
>Thanks,
>Alex
>
>Priscilla Oppenheimer wrote:
>>At 01:06 PM 9/26/01, khramov wrote:
>> > From my understanding ip dhcp-server command will enable upd broadcast
>> > on ports 66 and 67. Is that true?
>>
>>It causes your router to BE a DHCP server and to accept and process
>>broadcasts to UDP port 67 and to send responses from port 66. It does not
>>cause the router to forward UDP broadcasts to port 67.
>>
>>If you turn your router into a DHCP server, you would also have to identify
>>an external File Transport Protocol (FTP), Trivial File Transfer Protocol
>>(TFTP), or remote copy protocol (rcp) server that you will use to store the
>>DHCP bindings database. The router will access that database. Here's more
>>info on turning your router into a DHCP server, which is often not a good
>>idea, in my opinion (because it detracts from the router's real jobs):
>>
>>http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr_c/ipcprt1/1cfdhcp.htm
>
>>
>>
>>Priscilla
>>
>> >Alex
>> >
>> >
>> >Priscilla Oppenheimer wrote:
>> >>Why do you want to turn your router into a DHCP server? I thought you
>> >>already had a DHCP server. You just need a helper address and
>> >>
>> >>ip forward-protocol udp 67
>> >>no ip forward-protocol 137
>> >>no ip forward-protocol 138
>> >>
>> >>The last two commands are because you said that NetBIOS broadcast
>> >>forwarding was causing problems for your NT server. When you have a
>> helper
>> >>address, the router forwards a bunch of UDP packets. You have to
>> configure
>> >>it to be more discerning.
>> >>
>> >>Priscilla
>> >>
>> >>At 09:24 AM 9/26/01, khramov wrote:
>> >> >Hello,
>> >> > ip dhcp-server works, I didn't specify it with a hyphen. So
>> >> would you
>> >> >agree
>> >> > that the best solution for me would be to disable ip directed
>> >> >broadcast, ip
>> >> > helper address and enable ip dhcp-server at the global
>> config? If I
>> >> >enable ip
>> >> > dhcp-server do I need to enable ip forward-protocol udp (ports
>> >> 66 and
>> >> >67)?
>> >> >
>> >> > Thanks a lot,
>> >> > Alex
>> >> >
>> >> >MADMAN wrote:
>> >> >
>> >> > > Hmm.. I haven't done it in a while so I tried it on a 7507 with
>> >> RSP8's and
>> >> > > an MSFC2,
>> >> > > they both accepted the command just fine but are not in the
>> >> config. So I
>> >> > > figured they
>> >> > > must be enabled by default so I did a no ip forward protocol udp
>> 67 and
>> >> > > wallah, there it
>> >> > > is!!!
>> >> > >
>> >> > > C7507MIX#conf t
>> >> > > Enter configuration commands, one per line. End with CNTL/Z.
>> >> > > C7507MIX(config)#no ip for
>> >> > > C7507MIX(config)#no ip forward-protocol udp 67
>> >> > > C7507MIX(config)#^Z
>> >> > > C7507MIX#wr t
>> >> > > Building configuration...ip kerberos source-interface any
>> >> > > ip classless
>> >> > > no ip forward-protocol udp bootps
>> >> > >
>> >> > > Dave
>> >> > >
>> >> > > khramov wrote:
>> >> > >
>> >> > > > I did that, but when I do sh run it is not showing up in config
>> >> file. I
>> >> > > > mean (ip
>> >> > > > forward-protocol udp 67).
>> >> > > > Is that the way it is suppose to be?
>> >> > > >
>> >> > > > MADMAN wrote:
>> >> > > >
>> >> > > > > Check "ip foward protocol"
>> >> > > > >
>> >> > > > > Dave
>> >> > > > >
>> >> > > > > khramov wrote:
>> >> > > > > >
>> >> > > > > > Hello
>> >> > > > > > How do I enable broadcast for DHCP server? I know
>> that ip
>> >> > > > > > helper enables UDP broadcast, but broadcast of netbios
>> >> > > > > > services causes some problems for win nt server. So I
>> guess
>> >> > > > > > to be more specific what can I do to forward udp
>> >> broadcast on
>> >> > > > > > ports 67 and 68 only?
>> >> > > > > >
>> >> > > > > > And another question that I have what exactly ip
>> >> > > > > > directed-broadcast command does? I've searched
>> Cisco's web
>> >> > > > > > site but I never came across a clear defenition?
>> >> > > > > >
>> >> > > > > > Thanks,
>> >> > > > > > Alex
>> >> > > > > >
>> >> > > > > > [GroupStudy.com removed an attachment of type text/x-vcard
>> >> which had
>> >> >a
>> >> > > > name
>> >> > > > > > of khramov.vcf]
>> >> > > > > --
>> >> > > > > David Madland
>> >> > > > > Sr. Network Engineer
>> >> > > > > CCIE# 2016
>> >> > > > > Qwest Communications Int. Inc.
>> >> > > > > [EMAIL PROTECTED]
>> >> > > > > 612-664-3367
>> >> > > > >
>> >> > > > > "Emotion should reflect reason not guide it"
>> >> > > >
>> >> > > > [GroupStudy.com removed an attachment of type text/x-vcard which
>> >> had a
>> >> >name
>> >> > > > of khramov.vcf]
>> >> > > --
>> >> > > David Madland
>> >> > > CCIE# 2016
>> >> > > Senior Network Engineer
>> >> > > Qwest Communications
>> >> > > 612-664-3367
>> >> >
>> >> >[GroupStudy.com removed an attachment of type text/x-vcard which had a
>> >> name
>> >> >of khramov.vcf]
>> www.groupstudy.com/form/read.php?f=7&i=21133&t=21051>http://www.
>> >> groupstudy.com/form/read.php?f=7&i=21133&t=21051
>> >> >--------------------------------------------------
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>> >>________________________
>> >>
>> >>Priscilla Oppenheimer
>> >>http://www.priscilla.com>http://www.priscill
>> a.com
>>
>>________________________
>>
>>Priscilla Oppenheimer
>>http://www.priscilla.com
________________________
Priscilla Oppenheimer
http://www.priscilla.com
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