From: Jian Gu (guxiaojian@gmail.com)
Date: Mon Jan 15 2007 - 20:47:24 ART
You are right, the subnet mask is in option field.
On 1/15/07, Tony Schaffran <groupstudy@cconlinelabs.com> wrote:
>
> Here is a link that explains the DHCP process very clearly.
>
>
> http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a00800f0804.shtml#dhcppacket
>
> The subnet mask is is carried in the DHCP packet from the server to the
> client.
>
>
>
> Tony Schaffran
>
> Network Analyst
>
> CCIE #11071
>
> CCNP, CCNA, CCDA,
>
> NNCDS, NNCSS, CNE, MCSE
>
>
>
> www.cconlinelabs.com
>
> Your #1 choice for online Cisco rack rentals.
>
>
>
> -----Original Message-----
> *From:* Jian Gu [mailto:guxiaojian@gmail.com]
> *Sent:* Monday, January 15, 2007 2:04 PM
> *To:* Tony Schaffran
> *Cc:* Jim; ccie anees; ccielab@groupstudy.com
> *Subject:* Re: IOS DHCP issue
>
> If you study DHCP packets carefully, you will notice that network mask is
> not carried in any DHCP packets.
>
> On 1/15/07, Tony Schaffran < groupstudy@cconlinelabs.com> wrote:
> >
> > There is still a problem with your dhcp pool not matching the subnet of
> > vlan3.
> >
> > Tony Schaffran
> > Network Analyst
> > CCIE #11071
> > CCNP, CCNA, CCDA,
> > NNCDS, NNCSS, CNE, MCSE
> >
> > www.cconlinelabs.com
> > Your #1 choice for online Cisco rack rentals.
> >
> >
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> > Jim
> > Sent: Monday, January 15, 2007 11:21 AM
> > To: ccie anees
> > Cc: ccielab@groupstudy.com
> > Subject: Re: IOS DHCP issue
> >
> >
> > I tested the config through lab, it seems to work. Just like others
> > pointed to, there was issue before router rip betweening R1 and sw1,
> > because, R1 was sending unicast dhcp-offers to 129.1.3.7, but it didn't
> > have
> > that route. So it had no-where to send. After turning on rip, it
> > starts
> > working. Here is the configuration and the debug output.
> >
> >
> > R1
> > ####
> > interface FastEthernet0/0
> > ip address 129.1.17.1 255.255.255.0
> > !
> > no ip dhcp conflict logging
> > ip dhcp excluded-address 129.1.3.1 129.1.3.2
> > ip dhcp excluded-address 129.1.3.4 129.1.3.254
> > !
> > ip dhcp pool R3_Pool
> > network 129.1.3.0 255.255.255.0
> > default-router 129.1.3.7
> > !
> > router rip
> > no auto-summ
> > version 2
> > network 129.1.0.0
> >
> > SW1
> > ######
> > interface Vlan17
> > ip address 129.1.17.7 255.255.255.0
> > interface Vlan3
> > ip address 129.1.3.7 255.255.255.128
> > ip helper-address 129.1.17.1
> > router rip
> > no auto-summ
> > version 2
> > network 129.1.0.0
> >
> > R3
> > ###
> > interface FastEthernet3/0
> > ip address dhcp
> >
> >
> > Rack2R3(config)#int fa 0/0
> > Rack2R3(config-if)#ip add dhcp
> > Rack2R3(config-if)#
> > *Nov 30 16:41:52.994: %DHCP-6-ADDRESS_ASSIGN: Interface FastEthernet0/0
> > assigned DHCP address 129.1.3.3, mask 255.255.255.0, hostname Rack2R3
> >
> >
> > Rack2SW1(config-if)#
> > 2d21h: DHCPD: setting giaddr to 129.1.3.7.
> > 2d21h: DHCPD: BOOTREQUEST from
> >
> > 0063.6973.636f.2d30.3030.392e.3763.3735.2e35.3138.312d.4661.302f.30forwarded
> > to
> > 129.1.17.1.
> > 2d21h: DHCPD: forwarding BOOTREPLY to client 0009.7c75.5181.
> > 2d21h: DHCPD: broadcasting BOOTREPLY to client 0009.7c75.5181.
> > 2d21h: DHCPD: setting giaddr to 129.1.3.7.
> > 2d21h: DHCPD: BOOTREQUEST from
> >
> > 0063.6973.636f.2d30.3030.392e.3763.3735.2e35.3138.312d.4661.302f.30forwarded
> > to
> > 129.1.17.1.
> > 2d21h: DHCPD: forwarding BOOTREPLY to client 0009.7c75.5181.
> > 2d21h: DHCPD: broadcasting BOOTREPLY to client 0009.7c75.5181.
> >
> > Rack2R1#
> > *Mar 3 21:52:27.594 : DHCPD: DHCPDISCOVER received from client
> > 0063.6973.636f.2d30.3030.392e.3763.3735.2e35.3138.312d.4661.302f.30through
> > relay 129.1.3.7.
> > *Mar 3 21:52:29.594: DHCPD: Sending DHCPOFFER to client
> > 0063.6973.636f.2d30.3030.392e.3763.3735.2e35.3138.312d.4661.302f.30 (
> > 129.1.3.3).
> > *Mar 3 21:52:29.594: DHCPD: unicasting BOOTREPLY for client
> > 0009.7c75.5181to relay
> > 129.1.3.7.
> > *Mar 3 21:52:29.602: DHCPD: DHCPREQUEST received from client
> > 0063.6973.636f.2d30.3030.392e.3763.3735.2e35.3138.312d.4661.302f.30.
> > *Mar 3 21:52:29.602: DHCPD: Sending DHCPACK to client
> > 0063.6973.636f.2d30.3030.392e.3763.3735.2e35.3138.312d.4661.302f.30 (
> > 129.1.3.3).
> > *Mar 3 21:52:29.602: DHCPD: unicasting BOOTREPLY for client
> > 0009.7c75.5181to relay
> > 129.1.3.7.
> >
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