Re: DHCP and subnets
If you use a router for DHCP request forwarding using BOOTP IP Helper Address, the DHCP server will accurately assign IP addresses to the correct subnets from the correct scopes using the source IP address. That is unless the request comes from an Ethernet interface has multiple IP addresses assigned from different logical subnets. In that case, it seems to always assign an address from the scope of the lowest numerical IP network address assigned to that interface. Vern Stitt AE, ASE, CCNA, MCSE ""Dale E. Drummond"" <[EMAIL PROTECTED]> wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > The DHCP server knows what scope to pick the ip address from by looking at > the GIADDR field in the DHCP packet. When the router helpers a DHCP > request to the DHCP server it populates the GIADDR address with the > primary ip address of the router interface that the DHCP broadcast request > was received on. When the DHCP server receives the request it looks at > the GIADDR field then looks to see if it has a scope that matches the ip > subnet of the address in the GIADDR fields. If it does it assigns an ip > from that subnet. > > Hope this helps. > > Dale > > > > Date: Sun, 16 Jul 2000 20:35:20 -0500 > From: [EMAIL PROTECTED] > To: [EMAIL PROTECTED] > Cc: [EMAIL PROTECTED] > Subject: RE: DHCP and subnets > > [ The following text is in the "iso-8859-1" character set. ] > [ Your display is set for the "US-ASCII" character set. ] > [ Some characters may be displayed incorrectly. ] > > My 2c on this . > > When the DHCP broadcasts crosses the router ,it carries that routers mask > and ip info across to the dhcp server ( assuming helpder is there) > > the DHCP server on seeing that the reqest came from that particular subnet > issues an ip from a scope ...U could configure multiple scopes and combine > them into one superscope to do this. Hope this helps. > > Cheers,Padhu > > -Original Message- > From: whatshakin > To: [EMAIL PROTECTED] > Sent: 7/16/00 12:11 PM > Subject: DHCP and subnets > > Hello folks, > Please clarify this for me. > > Hypothetical example: Campus LAN with multiple buildings. Each building > on its own vlan and with its own subnet addressing scheme. All buildings > tied in to a Catalyst 5500 which has RSP doing all the inter-vlan > routing. Data center using a single DHCP server with multiple scopes > (one scope per vlan/subnet etc) to supply all vlans/subnets with their > respective ip addresses. I want to understand how the DHCP server knows > how to hand out the correct ip address from the corresponding subnet to > the workstations that request them. I have come to believe that > initially DHCP servers have no idea whom is requesting an address, they > just hand them out to whoever asks...this is what is confusing. I > understand that each Vlan needs its own gateway address where the > workstations aim their broadcasts and there an ip helper-address > statement in the RSP for each vlan, but I still don't understand how the > DHCP server knows how to hand out the appropriate address when it has > multiple scopes enabled. > > TIA for any clarification you can offer. > > > > Dale E Drummond [EMAIL PROTECTED] >http://www.pobox.com/~dale/ > > > > ___ > UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html > FAQ, list archives, and subscription info: http://www.groupstudy.com > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > --- ___ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: DHCP and subnets
The DHCP server knows what scope to pick the ip address from by looking at the GIADDR field in the DHCP packet. When the router helpers a DHCP request to the DHCP server it populates the GIADDR address with the primary ip address of the router interface that the DHCP broadcast request was received on. When the DHCP server receives the request it looks at the GIADDR field then looks to see if it has a scope that matches the ip subnet of the address in the GIADDR fields. If it does it assigns an ip from that subnet. Hope this helps. Dale Date: Sun, 16 Jul 2000 20:35:20 -0500 From: [EMAIL PROTECTED] To: [EMAIL PROTECTED] Cc: [EMAIL PROTECTED] Subject: RE: DHCP and subnets [ The following text is in the "iso-8859-1" character set. ] [ Your display is set for the "US-ASCII" character set. ] [ Some characters may be displayed incorrectly. ] My 2c on this . When the DHCP broadcasts crosses the router ,it carries that routers mask and ip info across to the dhcp server ( assuming helpder is there) the DHCP server on seeing that the reqest came from that particular subnet issues an ip from a scope ...U could configure multiple scopes and combine them into one superscope to do this. Hope this helps. Cheers,Padhu -Original Message- From: whatshakin To: [EMAIL PROTECTED] Sent: 7/16/00 12:11 PM Subject: DHCP and subnets Hello folks, Please clarify this for me. Hypothetical example: Campus LAN with multiple buildings. Each building on its own vlan and with its own subnet addressing scheme. All buildings tied in to a Catalyst 5500 which has RSP doing all the inter-vlan routing. Data center using a single DHCP server with multiple scopes (one scope per vlan/subnet etc) to supply all vlans/subnets with their respective ip addresses. I want to understand how the DHCP server knows how to hand out the correct ip address from the corresponding subnet to the workstations that request them. I have come to believe that initially DHCP servers have no idea whom is requesting an address, they just hand them out to whoever asks...this is what is confusing. I understand that each Vlan needs its own gateway address where the workstations aim their broadcasts and there an ip helper-address statement in the RSP for each vlan, but I still don't understand how the DHCP server knows how to hand out the appropriate address when it has multiple scopes enabled. TIA for any clarification you can offer. Dale E Drummond [EMAIL PROTECTED] http://www.pobox.com/~dale/ ___ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Fw: DHCP, and, subnets
The RSM work as the BOOTP Relay agent this is what happen when the client request for IP Address : 1 The request packet arrive to the interface (of the catalyst and RSM check this packet). As a note the DHCP request contain the Router Relay IP Address field in the packet). The client use UDP packet port 67. 2. The RSM will replace the Router Relay IP addess field in the packet with the ip address of the interface VLAN configured in the RSM.This will be usefull because the BOOTP server will use this address to relay its replay back toward the client via the relay agent, int this case is the RSM. 3. The RSM send the unicast packet from the Client request packet and send it to the Configured Helper Address. 4. When the BOOTP Server receive the request packet, the server will reply by using port 67 at the ip address that has been filled into the Relay router IP Address field by the relay agent. 5. The RSM ( as the relay agent ) then deliver the response to the client - using either broadcast or hardware Client Address. Correct me if it is wrong - Original Message - From: "Stephen Lee" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Sunday, July 16, 2000 9:02 PM Subject: Re: DHCP, and, subnets > Please correct me if I'm wrong but the way I've seen it work is; If you have > the helper address defined on all the vlans in you RSM then, when the router > sees a bootp dhcp request from the PC it sends a directed broadcast towards > the next hop to the helper address. When it gets to the server the packet > contains the originating subnet and the server then knows what subnet to > give an address from. It then sends a unicast packet back to the originating > router and the router then forwards it to the pc via its MAC address. > > In reply to: > Hello folks, > Please clarify this for me. =20 > > Hypothetical example: Campus LAN with multiple buildings. Each building = > on its own vlan and with its own subnet addressing scheme. All buildings = > tied in to a Catalyst 5500 which has RSP doing all the inter-vlan = > routing. Data center using a single DHCP server with multiple scopes = > (one scope per vlan/subnet etc) to supply all vlans/subnets with their = > respective ip addresses. I want to understand how the DHCP server knows = > how to hand out the correct ip address from the corresponding subnet to = > the workstations that request them. I have come to believe that = > initially DHCP servers have no idea whom is requesting an address, they = > just hand them out to whoever asks...this is what is confusing. I = > understand that each Vlan needs its own gateway address where the = > workstations aim their broadcasts and there an ip helper-address = > statement in the RSP for each vlan, but I still don't understand how the = > DHCP server knows how to hand out the appropriate address when it has = > multiple scopes enabled. > > TIA for any clarification you can offer. > > > > Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com > > ___ > UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html > FAQ, list archives, and subscription info: http://www.groupstudy.com > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > ___ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: DHCP, and, subnets
Please correct me if I'm wrong but the way I've seen it work is; If you have the helper address defined on all the vlans in you RSM then, when the router sees a bootp dhcp request from the PC it sends a directed broadcast towards the next hop to the helper address. When it gets to the server the packet contains the originating subnet and the server then knows what subnet to give an address from. It then sends a unicast packet back to the originating router and the router then forwards it to the pc via its MAC address. In reply to: Hello folks, Please clarify this for me. =20 Hypothetical example: Campus LAN with multiple buildings. Each building = on its own vlan and with its own subnet addressing scheme. All buildings = tied in to a Catalyst 5500 which has RSP doing all the inter-vlan = routing. Data center using a single DHCP server with multiple scopes = (one scope per vlan/subnet etc) to supply all vlans/subnets with their = respective ip addresses. I want to understand how the DHCP server knows = how to hand out the correct ip address from the corresponding subnet to = the workstations that request them. I have come to believe that = initially DHCP servers have no idea whom is requesting an address, they = just hand them out to whoever asks...this is what is confusing. I = understand that each Vlan needs its own gateway address where the = workstations aim their broadcasts and there an ip helper-address = statement in the RSP for each vlan, but I still don't understand how the = DHCP server knows how to hand out the appropriate address when it has = multiple scopes enabled. TIA for any clarification you can offer. Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com ___ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: DHCP and subnets
My 2c on this . When the DHCP broadcasts crosses the router ,it carries that routers mask and ip info across to the dhcp server ( assuming helpder is there) the DHCP server on seeing that the reqest came from that particular subnet issues an ip from a scope ...U could configure multiple scopes and combine them into one superscope to do this. Hope this helps. Cheers,Padhu -Original Message- From: whatshakin To: [EMAIL PROTECTED] Sent: 7/16/00 12:11 PM Subject: DHCP and subnets Hello folks, Please clarify this for me. Hypothetical example: Campus LAN with multiple buildings. Each building on its own vlan and with its own subnet addressing scheme. All buildings tied in to a Catalyst 5500 which has RSP doing all the inter-vlan routing. Data center using a single DHCP server with multiple scopes (one scope per vlan/subnet etc) to supply all vlans/subnets with their respective ip addresses. I want to understand how the DHCP server knows how to hand out the correct ip address from the corresponding subnet to the workstations that request them. I have come to believe that initially DHCP servers have no idea whom is requesting an address, they just hand them out to whoever asks...this is what is confusing. I understand that each Vlan needs its own gateway address where the workstations aim their broadcasts and there an ip helper-address statement in the RSP for each vlan, but I still don't understand how the DHCP server knows how to hand out the appropriate address when it has multiple scopes enabled. TIA for any clarification you can offer. ___ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
DHCP and subnets
Hello folks, Please clarify this for me. Hypothetical example: Campus LAN with multiple buildings. Each building on its own vlan and with its own subnet addressing scheme. All buildings tied in to a Catalyst 5500 which has RSP doing all the inter-vlan routing. Data center using a single DHCP server with multiple scopes (one scope per vlan/subnet etc) to supply all vlans/subnets with their respective ip addresses. I want to understand how the DHCP server knows how to hand out the correct ip address from the corresponding subnet to the workstations that request them. I have come to believe that initially DHCP servers have no idea whom is requesting an address, they just hand them out to whoever asks...this is what is confusing. I understand that each Vlan needs its own gateway address where the workstations aim their broadcasts and there an ip helper-address statement in the RSP for each vlan, but I still don't understand how the DHCP server knows how to hand out the appropriate address when it has multiple scopes enabled. TIA for any clarification you can offer.
