Network Working Group H. Deng
Internet-Draft China Mobile
Intended status: Standards Track July 2, 2008
Expires: January 3, 2009
DHCP Based Configuration of Mobile Node from Home Network
draft-deng-mip4-host-configuration-00
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Abstract
This document describes the mechanism for providing the host
configuration parameters needed for network service from home network
based on DHCPINFORM. DHCPINFORM message has been widely used by
client to obtain other configuration information and could be sent to
local broadcast address or server unicast address. Mobile IP
specification could support DHCPINFORM broadcast or unicast message
straightfully without any revision.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Home DHCP server's address unknown . . . . . . . . . . . . . . 4
2.1. MIP4 Co-CoA case . . . . . . . . . . . . . . . . . . . . . 4
2.2. MIP4 FA CoA Case . . . . . . . . . . . . . . . . . . . . . 8
3. Home DHCP server's address known . . . . . . . . . . . . . . . 13
4. Security Considerations . . . . . . . . . . . . . . . . . . . 16
5. IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 17
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18
7. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8. Normative References . . . . . . . . . . . . . . . . . . . . . 20
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 21
Intellectual Property and Copyright Statements . . . . . . . . . . 22
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1. Introduction
Mobile node could use DHCP mechanism to configure local information
when it attach to the foreign network. But it may have to get
configuration information from the home network as well. The common
mechanism to configure the mobile host is preferable in Mobile IP.
If a mobile node has obtained a network address through some other
means, it may use a DHCPINFORM request message to obtain other local
configuration parameters. This DHCPINFORM message could be sent to
local broadcast address or server unicast address(know it from out of
band delivery). DHCP Server receiving a DHCPINFORM message construct
a DHCPACK message with any local configuration parameters appropriate
for the mobile node.
This document has analysed the process about how Mobile IP
specification could straightfully support DHCPINFORM broadcast or
unicast message for host configuration without any revision.
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2. Home DHCP server's address unknown
2.1. MIP4 Co-CoA case
If the 'D' bit was set in the mobile node's Registration Request
message, and code field of the received registration reply indicate
successly registered. This means that the mobile node is using a co-
located care-of address.
Section 5.3 of Reverse tunneling [RFC3024] recommend that a mobile
node using a co-located care-of address send the broadcast/multicast
packet are handled according to Sections 4.3 and 4.4 of the Mobile IP
specification [RFC3344].
Section 4.3 of [RFC3344] doesn't specify how a mobile node send
datagrams to a broadcast address in detail. Section 4.4 of [RFC3344]
specify that a mobile node which tunnels a multicast datagram to its
home agent MUST use its home address as the IP source address of both
the (inner) broadcast datagram and the (outer) encapsulating
datagram. Anyway this tunnel is not topologically correct.
The mobile node simply tunnels appropriate broadcast DHCPINFORM
message to the home agent.The source address of this DHCPINFORM
message is the mobile node's home address. Home agent just work as a
simple DHCP relay agent as shown in figure 1.
+-----+ +-------+
| HA/ | | Home |
|DHCP |----| DHCP |
|Relay| | Server|
+-----+ +-------+
//
// Home Network
-------------//-----------------------
// Visiting Network
//
// +----+
+----+ | |
| MN |----| AR |
+----+ | |
+----+
Figure 1: Home network configuration in the case of Co-CoA
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+----+ +-------+ +------+
| | | HA | |DHCP |
| MN | | DHCP | |Server|
| | | relay | | |
+----+ +-------+ +------+
| RRQ | |
|--------------------------->| |
| RRP | |
|<---------------------------| |
| 1 | |
|--------------------------->| |
| | 2 |
| |--------->|
| | |
| | 3 |
| |<---------|
| 4 | |
|<---------------------------| |
Figure 2: Message sequence for host configuration in Co-CoA
Figure 2 shows the message sequence for host configuration in Co-CoA.
(1) After the mobile node successfully registered to the home agent
based on Registration Request(RRQ) and Registration Response(RRP)
message, it sends a DHCPINFORM message to request specific
configuration parameters by including the 'parameter request list'
option from home network. The mobile node generates and records a
random transaction identifier and inserts that identifier into the
'xid' field. The mobile node places its own home address in the
'ciaddr' field.
The mobile node will send DHCPINFORM message to the limited (all 1s)
broadcast address. DHCPINFORM messages MUST be directed to the 'DHCP
server' UDP port.
The mobile node will encapsulate this DHCPINFORM broadcast message
with IP in IP tunnel and send to the home agent, DHCPINFORM Packet
format sent by the mobile node is shown below:
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IP fields (encapsulating header):
Source Address = mobile node's home address
Destination Address = home agent's address
Protocol field: 4 (IP in IP)
IP fields (original header):
Source Address = mobile node's home address
Destination Address = broadcast address
UDP Src Port: bootpc(68), Dst Port: bootps(67)
Bootstrap Protocol:
field:
op = BOOTREQUEST
htype = Ethernet or (From "Assigned Numbers" RFC)
hlen = 6 or (Hardware address length in octets)
hops = 0
xid = selected by client
secs = 0
flags = 0
ciaddr = mobile node's home address
yiaddr = 0
siaddr = 0
giaddr = 0
chaddr = mobile node's MAC address
options:
option 53: DHCP Message Type = DHCPINFORM
option 61: Client Identifier = mobile node's MAC address
option 55: Parameter request List (Domain Name Server,... et al.)
(2) Since the home agent acts as the DHCP relay agent, after
receiving a unicast tunnel message, it detunneled the unicast
encapsulated header, and should look at the the 'giaddr' field of
DHCPINFORM message. If zero, it should plug its own IP address into
this field. It may also use the 'hops' field to optionally control
how far the packet is reforwarded. Hops should be incremented on
each forwarding.
DHCPINFORM Packet format forwarded by the home agent:
IP fields:
Source Address = home agent's address
Destination Address = DHCP server's address
UDP Src Port: bootps(67), Dst Port: bootps(67)
Bootstrap Protocol:
field:
giaddr = home agent's address
(3) DHCP server receiving a DHCPINFORM message construct a DHCPACK
message with any home configuration parameters appropriate for the
mobile node according to Section 3.4 of [RFC2131] . The DHCP server
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SHOULD unicast the DHCPACK reply to the address given in the 'giaddr'
field of the DHCPINFORM message.
DHCPACK Packet format sent by the DHCP Server:
IP fields:
Source Address = DHCP server's address
Destination Address = home agent's address
(from 'giaddr' of DHCPINFORM)
UDP Src Port: bootps(67), Dst Port: bootps(67)
Bootstrap Protocol:
field:
op = BOOTREPLY
htype = Ethernet or (From "Assigned Numbers" RFC)
hlen = 6 or (Hardware address length in octets)
hops = 0
xid = same as "xid" field of DHCPINFORM message
secs = 0
flags = 0
ciaddr = mobile node's home address (from 'ciaddr' of DHCPINFORM)
yiaddr = 0
siaddr = 0
giaddr = home agent's address (from 'giaddr' of DHCPINFORM)
chaddr = mobile node's MAC address (from 'chaddr' of DHCPINFORM)
options:
option 53: DHCP Message Type = DHCPACK
option 61: Server Identifier = DHCP server's MAC address
option 6: Domain Name Server
all other options: if needed
(4) The home agent intercepting a unicast DHCPACK message will
tunnels this datagram to the mobile node's currently registered
care-of address.
DHCPACK Packet format forwarded by the home agent:
IP fields (encapsulating header):
Source Address = home agent's address
Destination Address = mobile node's care-of-address
Protocol field: 4 (IP in IP)
IP fields (original header):
Source Address = DHCP server's address
Destination Address = mobile node's home address
UDP Src Port: bootps(67), Dst Port: bootpc(68)
Bootstrap Protocol
Once a DHCPACK message with an 'xid' field matching that in the
mobile node's DHCPINFORM message arrives from any server, the mobile
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node's configuration process is finished.
If the mobile node does not receive a DHCPACK within a reasonable
period of time (60 seconds or 4 tries if using timeout suggested in
section 4.1), then it SHOULD display a message informing the user of
the problem, and then SHOULD begin network processing using suitable
defaults as per Appendix A of [RFC2131].
2.2. MIP4 FA CoA Case
If the 'D' bit was not set in the mobile node's Registration Request
message, and code field of the received registration reply indicate
successly registered. This means that the mobile node is using a
foreign agent care-of address.
Reverse tunneling [RFC3024] in Mobile IP has mandate that a mobile
node using a foreign agent care-of address MUST use the encapsulating
delivery style. So the operation of DHCPINFORM broadcast message to
the home network in this case should follow the encapsulating
delivery style.
+-----+ +-------+
| HA/ |____| Home |
|DHCP |----| DHCP |
|Relay| | Server|
+-----+ +-------+
||
|| Home Network
----------------||--------------------
|| Visiting Network
||
+----+
+----+______| |
| MN |------| FA |
+----+ | |
+----+
Figure 3: Home network configuration in the case of FA-CoA
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+----+ +-----+ +-------+ +------+
| | | | | HA | |DHCP |
| MN | | FA | | DHCP | |Server|
| | | | | relay | | |
+----+ +-----+ +-------+ +------+
| | | |
| RRQ | |
|---------------------------->| |
| RRP | |
|<----------------------------| |
| 1 | | |
|-------------->| | |
| | 2 | |
| |------------>| |
| | | 3 |
| | |--------->|
| | | 4 |
| | |<---------|
| | 5 | |
| |<------------| |
| 6 | | |
|<--------------| | |
Figure 4: Message sequence for host configuration in FA-CoA
Figure 4 shows the message sequence for host configuration in Co-CoA.
(1) After the mobile node successfully registered to the home agent
based on Registration Request(RRQ) and Registration Response(RRP)
messages, it sends a DHCPINFORM message to request specific
configuration parameters by including the 'parameter request list'
option from home network. The mobile node generates and records a
random transaction identifier and inserts that identifier into the
'xid' field. The mobile node places its own home address in the
'ciaddr' field.
The mobile node send DHCPINFORM the message to the limited (all 1s)
broadcast address. DHCPINFORM messages MUST be directed to the 'DHCP
server' UDP port.
The mobile node will encapsulate this DHCPINFORM broadcast message
with IP in IP tunnel and send to the foriegn agent, DHCPINFORM Packet
format sent by the mobile node is shown below:
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IP fields (encapsulating header):
Source Address = mobile node's home address
Destination Address = foreign agent's address
Protocol field: 4 (IP in IP)
IP fields (original header):
Source Address = mobile node's home address
Destination Address = broadcast address
UDP Src Port: bootpc(68), Dst Port: bootps(67)
Bootstrap Protocol:
field:
op = BOOTREQUEST
htype = Ethernet or (From "Assigned Numbers" RFC)
hlen = 6 or (Hardware address length in octets)
hops = 0
xid = selected by client
secs = 0
flags = 0
ciaddr = mobile node's home address
yiaddr = 0
siaddr = 0
giaddr = 0
chaddr = mobile node's MAC address
options:
option 53: DHCP Message Type = DHCPINFORM
option 61: Client Identifier = mobile node's MAC address
option 55: Parameter request List (Domain Name Server,... et al.)
(2) Packet format forwarded by the foreign agent (Encapsulating
Delivery Style):
IP fields (encapsulating header):
Source Address = foreign agent's care-of-address
Destination Address = home agent's address
Protocol field: 4 (IP in IP)
IP fields (original header):
Source Address = mobile node's home address
Destination Address = broadcast address
UDP Src Port: bootpc(68), Dst Port: bootps(67)
Bootstrap Protocol
Since the home agent acts as the DHCP relay agent, after receiving a
unicast tunnel message, it detunneled the unicast encapsulated
header, and should look at the the 'giaddr' field of DHCPINFORM
message. If zero, it should plug its own IP address into this field.
It may also use the 'hops' field to optionally control how far the
packet is reforwarded. Hops should be incremented on each
forwarding.
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(3) DHCPINFORM Packet format forwarded by the home agent:
IP fields:
Source Address = home agent's address
Destination Address = DHCP server's address
UDP Src Port: bootps(67), Dst Port: bootps(67)
Bootstrap Protocol:
field:
giaddr = home agent's address
(4) DHCP server receiving a DHCPINFORM message construct a DHCPACK
message with any home configuration parameters appropriate for the
mobile node according to Section 3.4 of [RFC2131] . The DHCP server
SHOULD unicast the DHCPACK reply to the address given in the 'giaddr'
field of the DHCPINFORM message.
DHCPACK Packet format sent by the DHCP Server:
IP fields:
Source Address = DHCP server's address
Destination Address = home agent's address
(from 'giaddr' of DHCPINFORM)
UDP Src Port: bootps(67), Dst Port: bootps(67)
Bootstrap Protocol:
field:
op = BOOTREPLY
htype = Ethernet or (From "Assigned Numbers" RFC)
hlen = 6 or (Hardware address length in octets)
hops = 0
xid = same as "xid" field of DHCPINFORM message
secs = 0
flags = 0
ciaddr = mobile node's home address (from 'ciaddr' of DHCPINFORM)
yiaddr = 0
siaddr = 0
giaddr = home agent's address (from 'giaddr' of DHCPINFORM)
chaddr = mobile node's MAC address (from 'chaddr' of DHCPINFORM)
options:
option 53: DHCP Message Type = DHCPACK
option 61: Server Identifier = DHCP server's MAC address
option 6: Domain Name Server
all other options: if needed
(5) The home agent intercepting a unicast DHCPACK message will
tunnels this datagram to the foreign agent care-of address.
DHCPACK Packet format forwarded by the home agent:
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IP fields (encapsulating header):
Source Address = home agent's address
Destination Address = foreign agent's care-of-address
Protocol field: 4 (IP in IP)
IP fields (original header):
Source Address = DHCP server's address
Destination Address = mobile node's home address
UDP Src Port: bootps(67), Dst Port: bootpc(68)
Bootstrap Protocol
(6) DHCPACK Packet format forwarded by the foreign agent:
IP fields (encapsulating header):
Source Address = foreign agent's address
Destination Address = mobile node's home address
Protocol field: 4 (IP in IP)
IP fields (original header):
Source Address = DHCP server's address
Destination Address = mobile node's home address
UDP Src Port: bootps(67), Dst Port: bootpc(68)
Bootstrap Protocol
Once a DHCPACK message with an 'xid' field matching that in the
mobile node's DHCPINFORM message arrives from any server, the mobile
node's configuration process is finished.
If the mobile node does not receive a DHCPACK within a reasonable
period of time (60 seconds or 4 tries if using timeout suggested in
section 4.1), then it SHOULD display a message informing the user of
the problem, and then SHOULD begin network processing using suitable
defaults as per Appendix A of [RFC2131].
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3. Home DHCP server's address known
If a mobile node has obtained a DHCP server address through some
other means (how to obtain is out scope of this document), after
registration process, it may send a DHCPINFORM unicast message to
obtain other local configuration parameters.
According to Section 1.7 of [RFC3344], in the reverse direction,
datagrams sent by the mobile node are generally delivered to their
destination using standard IP routing mechanisms, not necessarily
passing through the home agent.
+----+ +-----+ +-------+ +------+
| | | | | | |DHCP |
| MN | | FA | | HA | |Server|
| | | | | | | |
+----+ +-----+ +-------+ +------+
| | | |
| RRQ | |
|---------------------------->| |
| RRP | |
|<----------------------------| |
| 1 | | |
|--------------------------------------->|
| | | 2 |
| | |<---------|
| | 3 | |
|<----------------------------| |
| | 3 | |
| |<------------| |
| 4 | | |
|<--------------| | |
Figure 5: Message sequence for Known DHCP server's address
Figure 5 shows the message sequence for host configuration with known
DHCP server's address.
(1) After the mobile node successfully registered to the home agent
based on Registration Request(RRQ) and Registration Response(RRP)
message, it then unicasts the DHCPINFORM to the DHCP server based on
standard IP routing mechanisms whatever it is co-colated care-of
address or foreign agent care-of address.
DHCPINFORM Packet format sent by the mobile node is shown below:
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IP fields:
Source Address = mobile node's home address
Destination Address = DHCP server's address
UDP Src Port: bootpc(68), Dst Port: bootps(67)
Bootstrap Protocol:
field:
op = BOOTREQUEST
htype = Ethernet or (From "Assigned Numbers" RFC)
hlen = 6 or (Hardware address length in octets)
hops = 0
xid = selected by client
secs = 0
flags = 0
ciaddr = mobile node's home address
yiaddr = 0
siaddr = 0
giaddr = 0
chaddr = mobile node's MAC address
options:
option 53: DHCP Message Type = DHCPINFORM
option 61: Client Identifier = mobile node's MAC address
option 55: Parameter request List (Domain Name Server,... et al.)
(2) DHCP server receiving a DHCPINFORM message construct a DHCPACK
message with any home configuration parameters appropriate for the
mobile node according to Section 3.4 of [RFC2131] . If the 'giaddr'
field is zero and the 'ciaddr' field is nonzero, then the DHCP server
SHOULD unicast the DHCPACK reply to the address given in the 'ciaddr'
field of the DHCPINFORM message.
DHCPACK Packet format sent by the DHCP Server:
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IP fields:
Source Address = DHCP server's address
Destination Address = mobile node's home address
(from 'ciaddr' of DHCPINFORM)
UDP Src Port: bootps(67), Dst Port: bootpc(68)
Bootstrap Protocol:
field:
op = BOOTREPLY
htype = Ethernet or (From "Assigned Numbers" RFC)
hlen = 6 or (Hardware address length in octets)
hops = 0
xid = same as "xid" field of DHCPINFORM message
secs = 0
flags = 0
ciaddr = mobile node's home address (from 'ciaddr' of DHCPINFORM)
yiaddr = 0
siaddr = 0
giaddr = 0
chaddr = mobile node's MAC address (from 'chaddr' of DHCPINFORM)
options:
option 53: DHCP Message Type = DHCPACK
option 61: Server Identifier = DHCP server's MAC address
option 6: Domain Name Server
all other options: if needed
(3,4) The home agent intercepting a unicast DHCPACK message will
tunnels this datagram to the mobile node's home address based on
standard mobile IP process.
According to Sections 5.5 and 5.6 of the Mobile IP specification
[RFC3344], the mobile node may create a tunnel to its home agent.
Then, datagrams destined for DHCP server will appear to emanate from
the home network. This kind of process could be refered to section 2
of this document.
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4. Security Considerations
This document just analyse the process of DHCPINFORM support in
mobile IP environment, it operates in the security constraints and
requirements of [RFC2131] and [RFC3344].
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5. IANA Consideration
This document makes no requests to IANA.
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6. Acknowledgments
The author thanks the discussion from Kent Leung, Alexandru Petrescu,
Charles E. Perkins, Jari Arkko, Vijay Devarapalli, Hans Sjostrand,
Peng Yang and et al. in the development of this document.
The efforts of McCann Peter and Henrik Levkowetz in reviewing this
document are gratefully acknowledged.
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7. Conclusion
This document verified that mobile node could get home network
configuration based on DHCPINFORM without any revision of basic
mobile IP specification.
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8. Normative References
[RFC0951] Croft, B. and J. Gilmore, "Bootstrap Protocol", RFC 951,
September 1985.
[RFC1700] Reynolds, J. and J. Postel, "Assigned Numbers", RFC 1700,
October 1994.
[RFC1701] Hanks, S., Li, T., Farinacci, D., and P. Traina, "Generic
Routing Encapsulation (GRE)", RFC 1701, October 1994.
[RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003,
October 1996.
[RFC2004] Perkins, C., "Minimal Encapsulation within IP", RFC 2004,
October 1996.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997.
[RFC3024] Montenegro, G., "Reverse Tunneling for Mobile IP,
revised", RFC 3024, January 2001.
[RFC3344] Perkins, C., "IP Mobility Support for IPv4", RFC 3344,
August 2002.
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Author's Address
Hui Deng
China Mobile
53A,Xibianmennei Ave.,
Xuanwu District,
Beijing 100053
China
Email: denghui02@gmail.com
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