From: NET HE (he_net@hotmail.com)
Date: Sun Mar 01 2009 - 23:29:58 ARST
You can use debug ip packet detail at relay agent to check packet flow.
Best Regards,
Net (Xin) He
> Date: Sun, 1 Mar 2009 23:23:05 +0000
> Subject: Re: DHCP packet exchange when using ip helper-address
> From: sadiqtanko@gmail.com
> To: cch.ccie@gmail.com
> CC: ccielab@groupstudy.com
>
> Hi Chan,
>
> The DHCP Server sends a unicast to the IP address of the interface where
the
> IP helper address is configured. Its is not a directed broadcast. A good
way
> to easily test and verify this is to configured the IP helper address on
any
> router interface, and turn off directed broadcast on the interface (which
is
> off by default on Cisco routers anyway), and see DHCP working find.
>
> I have not been able to get you a document for the packet flow, but you
> should find good info here:
>
>
http://www.cisco.com/en/US/docs/ios/ipaddr/configuration/guide/iad_dhcp_rly_a
gt_ps6350_TSD_Products_Configuration_Guide_Chapter.html
>
> Sadiq
>
> On Sun, Mar 1, 2009 at 11:02 PM, C Chan <cch.ccie@gmail.com> wrote:
>
> > Hi Expert,
> >
> > Whenever the DHCP server (eg 172.16.1.1) is located remotely, we ususally
> > use "ip helper-address 172.16.1.1" in local router interface (eg
> > 192.168.1.254) in order to grant IP address to local user. As I know, the
> > local router will unicast the DHCP packet (src 192.168.1.254 udp 67, dest
> > 172.16.1.1 udp 68) to DHCP server. How will the DHCP server reply? Does
it
> > unicast back the DHCP packet to router's interface (ie 192.168.1.254)? or
> > DHCP will reply to a directed-broadcast address of request LAN (ie
> > 192.168.1.*255*)?
> >
> > Where can I find a cisco official doc to describe the actual L3 packet
> > exchange?
> >
> > Chan
> >
> >
> > Blogs and organic groups at http://www.ccie.net
> >
> > _______________________________________________________________________
> > Subscription information may be found at:
> > http://www.groupstudy.com/list/CCIELab.html
> >
> >
> >
> >
> >
> >
> >
> >
>
>
> --
> CCIE #19963
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
>
>
>
>
>
>
>
This archive was generated by hypermail 2.1.4 : Mon Apr 06 2009 - 06:44:03 ART