Re: R/S giaddr

Sorry for trying to answer your questions with more questions but I was
wondering if you have dhcp helper or any relay set under the SVI? Can you
also show us the dhcp snooping configuration in global config and
interfaces of all devices in the stream? can you post the whole config for
R1?

Thanks

Marc

On Wednesday, March 28, 2012, Hasse wrote:

> !
> ip dhcp excluded-address 10.10.1.1 10.10.1.10
> !
> ip dhcp pool OK
> network 10.10.1.0 255.255.255.0
> domain-name ccie.net
> default-router 10.10.1.1
> lease 0 0 10
> !
>
> 2012/3/28 Israel Ogongo <ohio38jr_at_gmail.com>:
> > 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 c

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Received on Wed Mar 28 2012 - 07:46:01 ART