Priscilla, I'm wondering if you caught part of your trace? Specifically
this part:
Requested IP AddressDHCP Option
Option Code: 50 Requested IP Address
Option Length: 4
Address: 36.1.1.2
It's not common knowledge that DHCP has an option to request the IP address
during the original IP address request used the last time the end-host was
on the network. Microsoft's implementation definitely includes this.
Just a bit of trivia...
-- Leigh Anne
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
> Priscilla Oppenheimer
> Sent: Friday, October 05, 2001 5:45 PM
> To: [EMAIL PROTECTED]
> Subject: Re: DHCP communication [7:22272]
>
>
> You are in luck, sort of. In one of our previous tirades ;-)
> about DHCP, I
> sent the following message, which includes a DHCP Discover relayed by a
> router near the end. I can't send you the trace file, however, because it
> has some confidential stuff in it.
>
>
> Here's my config. The client is on the 36.1.1.0 network.
>
> I was sitting with my EtherPeek protocol analyzer on the
> 10.10.0.0 network.
> I could see the DHCP Discover come through to 10.10.0.1 as long as I used
> "ip helper-address 10.10.0.1."
>
> charlotte#s run
> Building configuration...
>
> Current configuration:
> !
> version 11.0
> service udp-small-servers
> service tcp-small-servers
> !
> hostname charlotte
> !
> enable password xxxx
> !
> interface Ethernet0
> ip address 10.10.0.2 255.255.255.0
> !
> interface Ethernet1
> ip address 36.1.1.1 255.255.255.0
> ip helper-address 10.10.0.1
> !
> interface Serial0
> ip address 192.168.40.2 255.255.255.0
> no fair-queue
> !
> interface Serial1
> no ip address
> shutdown
> !
> interface TokenRing1
> no ip address
> shutdown
> !
> interface TokenRing0
> no ip address
> shutdown
> !
> router ospf 100
> network 192.168.0.0 0.0.255.255 area 2
> network 10.10.0.0 0.0.255.255 area 0
> network 36.1.1.0 0.0.0.255 area 2
> !
> line con 0
> line aux 0
> transport input all
> line vty 0 4
> password cisco
> login
> !
> end
>
>
> The DHCP Discover from the client that I captured might be informative for
> people learning about how DHCP Relay works. Notice that the packet is a
> unicast, rather than a broadcast. Also, notice at the IP layer that the
> source address is the router, not the client's 0.0.0.0 address that you
> normally see with DHCP. The router also put its address in the DHCP server
> under "Gateway IP Address." The DHCP server needs to see this to
> know which
> subnet the client's request came from.
>
> Ethernet Header
> Destination: 00:00:0C:05:3E:80
> Source: 00:00:0C:00:2E:75
> Protocol Type:0x0800 IP
> IP Header - Internet Protocol Datagram
> Version: 4
> Header Length: 5 (20 bytes)
> Type of Service: %00000000
> Precedence: Routine, Normal Delay, Normal Throughput, Normal
> Reliability
> Total Length: 328
> Identifier: 12800
> Fragmentation Flags: %000 May Fragment Last Fragment
> Fragment Offset: 0 (0 bytes)
> Time To Live: 127
> Protocol: 17 UDP
> Header Checksum: 0xD998
> Source IP Address: 36.1.1.1
> Dest. IP Address: 10.10.0.1
> No IP Options
> UDP - User Datagram Protocol
> Source Port: 68 Bootstrap (BOOTP Client)
> Destination Port: 67 Bootstrap Protocol Server
> Length: 308
> Checksum: 0x3159
> BootP - Bootstrap Protocol
> Operation: 1 Boot Request
> Hardware Address Type: 1 Ethernet (10Mb)
> Hardware Address Length: 6 bytes
> Hops: 0
> Transaction ID: 678970121
> Seconds Since Boot Start: 0
> Flags: 0x0000
> IP Address Known By Client: 0.0.0.0 IP Address Not Known By Client
> Client IP Addr Given By Srvr: 0.0.0.0
> Server IP Address: 0.0.0.0
> Gateway IP Address: 36.1.1.1
> Client Hardware Address: 00:E0:98:89:52:FA
> Unused: 0x00000000000000000000
> Server Host Name:
> ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> Boot File Name:
> ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> DHCP - Dynamic Host Configuration Protocol
> DHCP Magic Cookie: 0x63825363
> Message TypeDHCP Option
> Option Code: 53 Message Type
> Option Length: 1
> Message Type: 1 Discover
> Client IdentifierDHCP Option
> Option Code: 61 Client Identifier
> Option Length: 7
> Hardware Type: 1
> Hardware Address: 00:E0:98:89:52:FA
> Requested IP AddressDHCP Option
> Option Code: 50 Requested IP Address
> Option Length: 4
> Address: 36.1.1.2
> Host Name AddressDHCP Option
> Option Code: 12 Host Name Address
> Option Length: 8
> String: MACTEAM.
> Vendor Class IdentifierDHCP Option
> Option Code: 60 Vendor Class Identifier
> Option Length: 7
> Option Data:
> MSFT 98 4D 53 46 54 20 39 38
> Parameter Request ListDHCP Option
> Option Code: 55 Parameter Request List
> Option Length: 9
> Requested Option: 1 Subnet Mask
> Requested Option: 15 Domain Name
> Requested Option: 3 Routers
> Requested Option: 6 Domain Name Servers
> Requested Option: 44 NetBIOS (TCP/IP) Name Servers
> Requested Option: 46 NetBIOS (TCP/IP) Node Type
> Requested Option: 47 NetBIOS (TCP/IP) Scope
> Requested Option: 43 Vendor Specific Information
> Requested Option: 77 User Class Information
> DHCP Option End
> Option Code: 255 End
> Extra bytes (Padding):
> ........... 00 00 00 00 00 00 00 00 00 00 00
> Frame Check Sequence: 0x00000000
>
>
> Priscilla
>
>
> At 05:44 PM 10/5/01, Lists Wizard wrote:
> >Hi Group,
> >
> >I am interested in the details (at the packet level) of DHCP
> communication
> >between the client and a DHCP server when there is a router in
> the middle.
> >Can any body provide me with sniffer trace of this kind of
> communication? I
> >use SnifferPro.
> >
> >Thanks
> >
> >Lists Wizard
> ________________________
>
> Priscilla Oppenheimer
> http://www.priscilla.com
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=22293&t=22272
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