From: Andy Mrozek (AndyMrozek@yahoo.com)
Date: Thu Dec 30 2004 - 01:11:47 GMT-3
Brian had mentioned he had it working via both the (ip helper-address
139.1.15.1 ) on the dialer 1 interface of r5 , and via using the (ip
dhcp-server 139.1.15.1) methods ,,, I see it working with the (ip
helper-address 139.1.15.1) on r5's dialer 1 interface if you use the
command on r4 of (ip address dhcp client-id FastEthernet0/0) as opposed
to the r4 command ( ip address negogiate <previous>) my question to
folks who have labbed this up what is the difference between these 2
commands:
1- ip address negotiate
2- ip address dhcp client-id
As I have yet to see that < ip address negotiate > command work when on
r4 with ip -helper address 139.1.15.1 on r5's dialer or bri physical
interface ??? Please anyone who has set this up we can test on my lab of
3640's ......... Either way config below does work just dont know the
functional diffs between 2 above commands....
### r4 ##### ip helper-address method
interface BRI0/0
no ip address
dialer pool-member 1
isdn switch-type basic-ni
isdn spid1 40811111
isdn spid2 40811112
end
interface Dialer1
ip address dhcp client-id FastEthernet0/0
ip rip advertise 3
encapsulation ppp
dialer pool 1
dialer idle-timeout 0
dialer string 2222
dialer string 2221
dialer-group 1
no cdp enable
end
######### R5 ############
interface BRI0/0
no ip address
dialer pool-member 1
isdn switch-type basic-ni
isdn spid1 40822221
isdn spid2 40822222
end
interface Dialer1
ip address 139.1.45.5 255.255.255.0
ip helper-address 139.1.15.1
ip rip advertise 3
encapsulation ppp
dialer pool 1
dialer string 1111
dialer watch-group 1
dialer-group 1
peer default ip address dhcp
no cdp enable
end
Joe Smith wrote:
> Tim,
>
> The DHCP request is coming from R4 and therefore is two hops away. If
> the TTL is one when it reaches the R5 isdn interface, and R5 does its
> job and subtracts one, the TTL reaches zero and is never forwarded to
> R1. This is supported by the DOC CD, which states "The IP
> time-to-live (TTL) value must be at least 2" for ip helper-address.
>
> We know that a Windows box requesting a DHCP address has a TTL greater
> then one, does a Cisco router? I would guess it would, but I can't
> test since I don't have access to my equipment until next week.
>
> Also of interest in the DOC CD The MAC address of the received frame
> must be all-ones broadcast address (ffff.ffff.ffff). Obviously an
> ISDN frame does not have a MAC address, but it states all conditions
> must be met.
>
> J3
>
>
>> From: "ccie2be" <ccie2be@nyc.rr.com>
>> To: "Joe Smith" <j333smith@hotmail.com>, <ccielab@groupstudy.com>
>> Subject: Re: I E lab 13 - dhcp-server vs ip helper
>> Date: Wed, 29 Dec 2004 19:41:23 -0500
>>
>> Joe,
>>
>> That's a good point to keep in mind.
>>
>> In the scenario I was working with, that couldn't be an issue - the dhcp
>> server was one hop
>>
>> from the dhcp relay.
>>
>> R4 --- isdn --- R5 ---- R1 (dhcp server)
>>
>> thanks for pointing that out.
>> ----- Original Message -----
>> From: "Joe Smith" <j333smith@hotmail.com>
>> To: <ccielab@groupstudy.com>
>> Sent: Wednesday, December 29, 2004 6:49 PM
>> Subject: Re: I E lab 13 - dhcp-server vs ip helper
>>
>>
>> > Tim,
>> >
>> > Do you know the TTL of the DHCP request? If its one, then ip helper
>> > wouldn't work per the Doc CD, however the Doc CD has no TTL
>> requirement
>> for
>> > ip dhcp-server.
>> >
>> > Just a thought.
>> >
>> > J3
>> >
>> >
>> > >From: "ccie2be" <ccie2be@nyc.rr.com>
>> > >Reply-To: "ccie2be" <ccie2be@nyc.rr.com>
>> > >To: "Joe Smith" <j333smith@hotmail.com>, <ccielab@groupstudy.com>
>> > >Subject: Re: I E lab 13 - dhcp-server vs ip helper
>> > >Date: Wed, 29 Dec 2004 16:17:22 -0500
>> > >
>> > >Joe,
>> > >
>> > >On the chance that you were right, I manually added the global, ip
>> > >forward-protocol, command
>> > >
>> > >to see if that would make a difference.
>> > >
>> > >Unfortunately, it didn't.
>> > >
>> > >I don't understand this.
>> > >
>> > >Using the dhcp-server command works. Using the ip helper-address
>> doesn't.
>> > >
>> > >I even rebooted the router after making the change just to make sure.
>> > >
>> > >Could it possibly be that I need to change something else in
>> addition to
>> > >the
>> > >above?
>> > >
>> > >(To test the above, I just removed the dhcp-server and added the ip
>> helper
>> > >command.)
>> > >
>> > >Tim
>> > >----- Original Message -----
>> > >From: "Joe Smith" <j333smith@hotmail.com>
>> > >To: <ccielab@groupstudy.com>
>> > >Sent: Wednesday, December 29, 2004 1:38 PM
>> > >Subject: Re: I E lab 13 - dhcp-server vs ip helper
>> > >
>> > >
>> > > > Then I'm mistaken! Well sort of since you still need it.
>> > > >
>> > > > J3
>> > > >
>> > > > >From: "ccie2be" <ccie2be@nyc.rr.com>
>> > > > >To: "Joe Smith" <j333smith@hotmail.com>, <ccielab@groupstudy.com>
>> > > > >Subject: Re: I E lab 13 - dhcp-server vs ip helper
>> > > > >Date: Wed, 29 Dec 2004 13:31:22 -0500
>> > > > >
>> > > > >Actually, according to the Doc-Cd, ip forword-protocol, is
>> enabled by
>> > > > >default.
>> > > > >
>> > > > >When the ip helper command is used only to forward dhcp/bootp
>> messages,
>> > >you
>> > > > >may want to disabled the
>> > > > >
>> > > > >forwarding of other protocols which are also forwarded by
>> default by
>> > >using
>> > > > >no ip forword prot xxx.
>> > > > >
>> > > > >
>> > > > >----- Original Message -----
>> > > > >From: "Joe Smith" <j333smith@hotmail.com>
>> > > > >To: <ccielab@groupstudy.com>
>> > > > >Sent: Wednesday, December 29, 2004 1:17 PM
>> > > > >Subject: RE: I E lab 13 - dhcp-server vs ip helper
>> > > > >
>> > > > >
>> > > > > > If I'm not mistaken don't you also need the "ip
>> forward-protocol"
>> > > > >command
>> > > > >in
>> > > > > > combination with the ip helper?
>> > > > > >
>> > > > > > J3
>> > > > > >
>> > > > > > >From: "ccie2be" <ccie2be@nyc.rr.com>
>> > > > > > >Reply-To: "ccie2be" <ccie2be@nyc.rr.com>
>> > > > > > >CC: "Group Study" <ccielab@groupstudy.com>
>> > > > > > >Subject: I E lab 13 - dhcp-server vs ip helper
>> > > > > > >Date: Wed, 29 Dec 2004 12:59:39 -0500
>> > > > > > >
>> > > > > > >Hi guys,
>> > > > > > >
>> > > > > > >R4's bri interface is configured to have it's ip address
>> > >negotiated.
>> > > > > > >
>> > > > > > >R5 is configured as a dhcp relay & is suppose to get an ip
>> address
>> > > > > > >
>> > > > > > >for R4 from a dhcp server configured on R1.
>> > > > > > >
>> > > > > > >R4 --isdn --- R5 ----- R1 (dhcp server).
>> > > > > > >
>> > > > > > >This works as it's suppose to when R5 has the global command,
>> > > > > > >
>> > > > > > >ip dhcp-server 139.1.15.1, configured.
>> > > > > > >
>> > > > > > >But, if the interface command, ip helper 139.1.15.1, is
>> configured
>> > >on
>> > > > > > >
>> > > > > > >R5, then R4 doesn't get an ip address.
>> > > > > > >
>> > > > > > >Can anyone explain why that is?
>> > > > > > >
>> > > > > > >I thought, the ip dhcp-server command does the same thing
>> as the
>> ip
>> > > > >helper
>> > > > > > >command except
>> > > > > > >
>> > > > > > >that it's more specific.
>> > > > > > >
>> > > > > > >TIA, Tim
>> > > > > > >
>> > > > > >
>> > >
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