DHCP relay question

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Hi,

I'm setting up a DHCP server with a Scope of 5000 IPs. Briefly, heres
my setup:

(Mobiles) -> Cisco Router -> DHCP Server


The DHCP server has a physical NIC IP of 20.20.20.113, no aliases, the
Cisco router has lots of IP routes, one of them being a vlan for the
20.20.20/24 network. The local loopback IP of the Cisco is
172.19.241.36. The DHCP scope is set for 172.19.192.1 - 172.19.223.254,
a single scope.

When one of the Mobiles sends a request, the Cisco is putting in a Relay
agent IP of 172.19.241.36. But the DHCP server is ignoring it.

Here is an Ethereal packet taken from snooping the 20.20.20.x vlan
network (the same vlan that the DHCP server is on).

I see the Discover, but no replies at all.

I'm looking for answers to two things:

1) How can I get the MS server to serve DHCP requests to the 172.19.192
network, even if the source address isn't in that range (my answer: I
don't think I can)

2) Although I see the DHCP Discover request going out from the Cisco, I
see nothing in the DHCP log file about reciving the request and
rejecting it or ignoring it (is this normal) - is there any more debug I
can turn on? I need to confirm the Discover packet reaching the DHCP
server.

My thinking is that the Cisco server *should* put in an IP of 20.20.20.x
as the relay IP and thats why its not working, but I'm not sure.

Cheers,

Adrian



MS DHCP LOG:

00,05/17/05,13:32:03,Started,,,
51,05/17/05,13:32:03,Authorization succeeded,,uk-lab.lucent.com,
55,05/17/05,13:32:28,Authorized(servicing),,uk-lab.lucent.com,
51,05/17/05,14:32:28,Authorization succeeded,,uk-lab.lucent.com,
51,05/17/05,15:33:02,Authorization succeeded,,uk-lab.lucent.com,
51,05/17/05,16:33:35,Authorization succeeded,,uk-lab.lucent.com,
51,05/17/05,17:34:07,Authorization succeeded,,uk-lab.lucent.com,
51,05/17/05,18:34:39,Authorization succeeded,,uk-lab.lucent.com,
51,05/17/05,19:35:13,Authorization succeeded,,uk-lab.lucent.com,
51,05/17/05,20:35:45,Authorization succeeded,,uk-lab.lucent.com,
51,05/17/05,21:36:17,Authorization succeeded,,uk-lab.lucent.com,
51,05/17/05,22:36:50,Authorization succeeded,,uk-lab.lucent.com,
51,05/17/05,23:37:23,Authorization succeeded,,uk-lab.lucent.com,



PACKET:

No. Time Source Destination Protocol
Info
17 14.362762 172.19.241.36 20.20.20.113 DHCP
DHCP Discover - Transaction ID 0x1261d

Frame 17 (618 bytes on wire, 618 bytes captured)
Arrival Time: May 17, 2005 13:54:33.854749000
Time delta from previous packet: 14.362762000 seconds
Time since reference or first frame: 14.362762000 seconds
Frame Number: 17
Packet Length: 618 bytes
Capture Length: 618 bytes
Protocols in frame: eth:ip:udp:bootp
Ethernet II, Src: 00:03:fe:ad:b3:b0, Dst: 00:a0:24:a8:6e:89
Destination: 00:a0:24:a8:6e:89 (3com_a8:6e:89)
Source: 00:03:fe:ad:b3:b0 (Cisco_ad:b3:b0)
Type: IP (0x0800)
Internet Protocol, Src Addr: 172.19.241.36 (172.19.241.36), Dst Addr:
20.20.20.113 (20.20.20.113)
Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
0000 00.. = Differentiated Services Codepoint: Default (0x00)
.... ..0. = ECN-Capable Transport (ECT): 0
.... ...0 = ECN-CE: 0
Total Length: 604
Identification: 0x8f65 (36709)
Flags: 0x00
0... = Reserved bit: Not set
.0.. = Don't fragment: Not set
..0. = More fragments: Not set
Fragment offset: 0
Time to live: 255
Protocol: UDP (0x11)
Header checksum: 0x646e (correct)
Source: 172.19.241.36 (172.19.241.36)
Destination: 20.20.20.113 (20.20.20.113)
User Datagram Protocol, Src Port: bootpc (68), Dst Port: bootps (67)
Source port: bootpc (68)
Destination port: bootps (67)
Length: 584
Checksum: 0x0000 (none)
Bootstrap Protocol
Message type: Boot Request (1)
Hardware type: Ethernet
Hardware address length: 6
Hops: 0
Transaction ID: 0x0001261d
Seconds elapsed: 0
Bootp flags: 0x0000 (Unicast)
0... .... .... .... = Broadcast flag: Unicast
.000 0000 0000 0000 = Reserved flags: 0x0000
Client IP address: 0.0.0.0 (0.0.0.0)
Your (client) IP address: 0.0.0.0 (0.0.0.0)
Next server IP address: 0.0.0.0 (0.0.0.0)
Relay agent IP address: 172.19.241.36 (172.19.241.36)
Client MAC address: 00:03:fe:ad:b3:b0 (Cisco_ad:b3:b0)
Server host name not given
Boot file name not given
Magic cookie: (OK)
Option 53: DHCP Message Type = DHCP Discover
Option 57: Maximum DHCP Message Size = 1152
Option 61: Client identifier (22 bytes)
Option 55: Parameter Request List
1 = Subnet Mask
6 = Domain Name Server
15 = Domain Name
44 = NetBIOS over TCP/IP Name Server
Option 52: Option Overload = Boot file and server host names hold
options
Boot file name option overload
Padding
Server host name option overload
Padding
End Option
Padding