Re: R/S giaddr

Hi,

Perhaps you would want to post your config on the DHCP router?

On Wed, Mar 28, 2012 at 11:56 AM, Hasse <eriksson.hans_at_gmail.com> wrote:

> Topology:
> R1-DHCP-Server------SW1---------SW2-------R3-CLIENT
> |
> R2-Client
>
> R1 DHCP Server connected to SW1
> R2 DHCP Client connected to SW1
> R3 DHCP Client Connected to SW2
> SW1 and SW2 dot1q trunk
> Vlan 10 on all
>
> Question 1:
> Where or when does DHCP snooping interrupt and write to the Snooping DB?
> Does Snooping place a place holder in the DB when the switch see the
> DHCPREG?
> and writing the DB when seeing the ACK?
>
> Question 2:
>
> When using a cisco router as a DHCP server in my case R1 connected to
> SW1 and Client R2.
> I recive the following error:
> *Mar 28 07:37:53.462: DHCPD: inconsistent relay information.
> *Mar 28 07:37:53.462: DHCPD: relay information option exists, but
> giaddr is zero.
> Why?
> My options are as follow
>
> 1) Turn off option 82 on the switch
> (no ip dhcp snooping information option)
> 2) On the DHCP server R1
> (ip dhcp relay information trusted)
> 3) ?
> 4) ?
>
> Question 3:
> I do not understand this problem fully, about giaddr.
>
>
> This server and Client are sitting on the same subnet. That is why I
> get the error. According to RFC I should be able to use following.
>
> The server SHOULD select the IP address the server is using for
> communication on that subnet as the 'server identifier'.
>
> Giaddr = Relay agent ip address used in booting via a relay agent.
>
> Giaddr from RFC 2131
>
>
> If 'giaddr' is 0x0 in the DHCPREQUEST message, the client is on
> the same subnet as the server. The server MUST
> broadcast the DHCPNAK message to the 0xffffffff broadcast address
> because the client may not have a correct network address or subnet
> mask, and the client may not be answering ARP requests.
> Otherwise, the server MUST send the DHCPNAK message to the IP
> address of the BOOTP relay agent, as recorded in 'giaddr'. The
> relay agent will, in turn, forward the message directly to the
> client's hardware address, so that the DHCPNAK can be delivered even
> if the client has moved to a new network.
>
>
> The 'server identifier' field is used both to identify a DHCP server
> in a DHCP message and as a destination address from clients to
> servers. A server with multiple network addresses MUST be prepared
> to to accept any of its network addresses as identifying that server
> in a DHCP message. To accommodate potentially incomplete network
> connectivity, a server MUST choose an address as a 'server
> identifier' that, to the best of the server's knowledge, is reachable
> from the client. For example, if the DHCP server and the DHCP client
> are connected to the same subnet (i.e., the 'giaddr' field in the
> message from the client is zero), the server SHOULD select the IP
> address the server is using for communication on that subnet as the
> 'server identifier'. If the server is using multiple IP addresses on
> that subnet, any such address may be used. If the server has
> received a message through a DHCP relay agent, the server SHOULD
> choose an address from the interface on which the message was
> recieved as the 'server identifier' (unless the server has other,
> better information on which to make its choice). DHCP clients MUST
> use the IP address provided in the 'server identifier' option for any
> unicast requests to the DHCP server.
>
> DHCP messages broadcast by a client prior to that client obtaining
> its IP address must have the source address field in the IP header
> set to 0.
>
>
>
>
>
>
>
>
>
> On R1 DHCP Server
>
> *Mar 28 07:37:57.462: DHCPD: inconsistent relay information.
> *Mar 28 07:37:57.462: DHCPD: relay information option exists, but
> giaddr is zero.
> *Mar 28 07:38:15.462: DHCPD: inconsistent relay information.
> *Mar 28 07:38:15.462: DHCPD: relay information option exists, but
> giaddr is zero.
> *Mar 28 07:38:18.462: DHCPD: inconsistent relay information.
> *Mar 28 07:38:18.462: DHCPD: relay information option exists, but
> giaddr is zero.
> *Mar 28 07:38:22.462: DHCPD: inconsistent relay information.
> *Mar 28 07:38:22.462: DHCPD: relay information option exists, but
> giaddr is zero.
>
> On Switch1
> 0x52 0x12 0x1 0x6 0x0 0x4 0x0 0xA 0x1 0x4 0x2 0x8 0x0 0x6 0x0 0x1A
> 0xE3 0x31 0xF 0x0
> *Mar 6 15:13:28.826: DHCP_SNOOPING_SW: bridge packet get invalid mat
> entry: FFFF.FFFF.FFFF, packet
> is flooded to ingress VLAN: (10)
> *Mar 6 15:13:32.358: DHCPSNOOP(hlfm_set_if_input): Setting if_input
> to Fa1/0/2 for pak. Was not set
> *Mar 6 15:13:32.358: DHCPSNOOP(hlfm_set_if_input): Clearing if_input
> for pak. Was Fa1/0/2
> *Mar 6 15:13:32.358: DHCPSNOOP(hlfm_set_if_input): Setting if_input
> to Fa1/0/2 for pak. Was not set
> *Mar 6 15:13:32.358: DHCP_SNOOPING: received new DHCP packet from
> input interface (FastEthernet1/0/2)
> *Mar 6 15:13:32.366: DHCP_SNOOPING: process new DHCP packet, message
> type: DHCPDISCOVER, input interface: Fa1/0/2, MAC da: ffff.ffff.ffff,
> MAC sa: 001d.46d1.fc68, IP da: 255.255.255.255, IP sa: 0.0.0.0, DHCP
> ciaddr: 0.0.0.0, DHCP yiaddr: 0.0.0.0, DHCP siaddr: 0.0.0.0, DHCP
> giaddr: 0.0.0.0, DHCP chaddr: 001d.46d1.fc68
> *Mar 6 15:13:32.366: DHCP_SNOOPING: add relay information option.
> *Mar 6 15:13:32.366: DHCP_SNOOPING_SW: Encoding opt82 CID in
> vlan-mod-port format
> *Mar 6 15:13:32.366: DHCP_SNOOPING_SW: Encoding opt82 RID in MAC address
> format
> *Mar 6 15:13:32.366: DHCP_SNOOPING: binary dump of relay info option,
> length: 20 data:
> 0x52 0x12 0x1 0x6 0x0 0x4 0x0 0xA 0x1 0x4 0x2 0x8 0x0 0x6 0x0 0x1A
> 0xE3 0x31 0xF 0x0
> *Mar 6 15:13:32.366: DHCP_SNOOPING_SW: bridge packet get invalid mat
> entry: FFFF.FFFF.FFFF, packet is flooded to ingress VLAN: (10)
> *Mar 6 15:13:36.359: DHCPSNOOP(hlfm_set_if_input): Setting if_input
> to Fa1/0/2 for pak. Was not set
> *Mar 6 15:13:36.359: DHCPSNOOP(hlfm_set_if_input): Clearing if_input
> for pak. Was Fa1/0/2
> *Mar 6 15:13:36.359: DHCPSNOOP(hlfm_set_if_input): Setting if_input
> to Fa1/0/2 for pak. Was not set
> *Mar 6 15:13:36.359: DHCP_SNOOPING: received new DHCP packet from
> input interface (FastEthernet1/0/2)
> *Mar 6 15:13:36.359: DHCP_SNOOPING: process new DHCP packet, message
> type: DHCPDISCOVER, input interfac
>
>
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Received on Wed Mar 28 2012 - 13:55:08 ART