| Re: Issue 5: Proposed text for Benefits of Using UDP-Lite? | <– Date –> <– Thread –> |
From: Pat Calhoun (pacalhou) (pcalhoun cisco.com)
|
|
| Date: Fri, 16 Nov 2007 15:36:30 -0800 (PST) | |
This issue is marked closed as no comments have been received since
posting
the proposed text on 10/12/07. It is fixed in
draft-ietf-capwap-protocol-
specification-08.txt
PatC
-----Original Message-----
From: Pat Calhoun (pacalhou)
Sent: Friday, October 12, 2007 11:32 AM
To: capwap [at] frascone.com
Subject: [Capwap] Issue 5: Proposed text for Benefits of Using UDP-Lite?
All,
Please find the proposed text for the IPv6/UDP-Lite issue below.
<proposed text>
3. CAPWAP Transport
Communication between a WTP and an AC is established using the
standard UDP client/server model. The CAPWAP protocol supports both
UDP and UDP-Lite [11] transport protocols. When run over IPv4, UDP
is used for the CAPWAP control and data channels.
When run over IPv6, the CAPWAP control channel always uses UDP, while
the CAPWAP data channel may use either UDP or UDP-Lite. UDP-Lite is
the default transport protocol for the CAPWAP data channel. However,
if a middlebox or IPv4 to IPv6 gateway has been discovered, UDP is
used for the CAPWAP data channel.
This section describes how the CAPWAP protocol is carried over IP and
UDP/UDP-Lite transport protocols. The CAPWAP Transport Protocol
message element Section 4.6.12 describes the rules to use in
determing which transport protocol is to be used.
3.1. UDP Transport
One of the CAPWAP protocol requirements is to allow a WTP to reside
behind a middlebox, firewall and/or Network Address Translation (NAT)
device. Since a CAPWAP session is initiated by the WTP (client) to
the well-known UDP port of the AC (server), the use of UDP is a
logical choice. The UDP checksum field in CAPWAP packets MUST be set
to zero.
CAPWAP protocol control packets sent from the WTP to the AC use the
CAPWAP control channel, as defined in Section 1.4. The CAPWAP
control port at the AC is the well known UDP port [to be IANA
assigned]. The CAPWAP control port at the WTP can be any port
selected by the WTP.
CAPWAP protocol data packets sent from the WTP to the AC use the
CAPWAP data channel, as defined in Section 1.4. The CAPWAP data port
at the AC is the well known UDP port [to be IANA assigned]. The
CAPWAP data port at the WTP can be any port selected by the WTP.
3.2. UDP-Lite Transport
When CAPWAP is run over IPv6, UDP-Lite is the default transport
protocol, which reduces the checksum processing required for each
packet (compared to the use of UDP over IPv6 [13]). When UDP-Lite is
used, the checksum field MUST have a coverage of 8 [11].
UDP-Lite uses the same port assignments as UDP.
[...]
4.6. CAPWAP Protocol Message Elements
[...]
CAPWAP Message Element Type Value
[...]
CAPWAP Transport Protocol TBD
CAPWAP Local IPV4 Address TBD
CAPWAP Local IPV6 Address TBD
[...]
4.6.12. CAPWAP Transport Protocol
When CAPWAP is run over IPv6, the UDP-Lite or UDP transports MAY be
used (see Section 3). The CAPWAP IPv6 Transport Protocol message
element is used by either the WTP or the AC to signal which transport
protocol is to be used for the CAPWAP data channel.
Upon receiving the Join Request, the AC MAY set the CAPWAP Transport
Protocol to UDP-Lite in the Configuration Status Request or Image
Data Request message if the CAPWAP message was received over IPv6,
and the CAPWAP Local IPv6 Address message element (see
Section 4.6.14) is present and the address matches the packet's
source IP address.
Upon receiving the Configuration Status Request or Image Data Request
message, the WTP MAY set the CAPWAP Transport Protocol to UDP-Lite in
the Configuration Status Response or Image Data Response message if
the message was received over IPv6, and the CAPWAP Local IPv6 Address
message element (see Section 4.6.14) is present and the address
matches the packet's source IP address.
For any other condition, the CAPWAP Transport Protocol MUST be set to
UDP.
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Transport |
+-+-+-+-+-+-+-+-+
Type: TBD for CAPWAP Transport Protocol
Length: 1
Transport: The transport to use for the CAPWAP data channel.
1 - UDP-Lite The UDP-Lite transport protocol is to be used for
the CAPWAP data channel. Note that this option is illegal is
either the WTP or the AC uses IPv4.
2 - UDP The UDP transport protocol is to be used for the CAPWAP
data channel.
4.6.13. CAPWAP Local IPv4 Address
The CAPWAP Local IPv4 Address message element is sent by either the
WTP or the AC in the Join Request, Configuration Status Request or
Image Data Request message in order to communicate the IP Address of
the transmitter. The receiver uses this to determine whether a
middlebox exists between the two peers, by comparing the source IP
address of the packet against the value of the message element.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: TBD for CAPWAP Local IPv4 Address
Length: 4
IP Address: The IP Address of the sender.
4.6.14. CAPWAP Local IPv6 Address
The CAPWAP Local IPv6 Address message element is sent by either the
WTP or the AC in the Discovery Response or Join Request in order to
communicate the IP Address of the transmitter. The receiver uses
this to determine whether a middlebox exists between the two peers,
by comparing the source IP address of the packet against the value of
the message element.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: TBD for CAPWAP Local IPv6 Address
Length: 16
IP Address: The IP Address of the sender.
[...]
11. NAT Considerations
There are three specific situations in which a NAT deployment may be
used in conjunction with a CAPWAP-enabled deployment. The first
consists of a configuration in which a single WTP is behind a NAT
system. Since all communication is initiated by the WTP, and all
communication is performed over IP using two UDP ports, the protocol
easily traverses NAT systems in this configuration.
In the second case, two or more WTPs are deployed behind the same NAT
system. Here, the AC would receive multiple connection requests from
the same IP address, and cannot differentiate the originating WTP of
the connection requests. The CAPWAP Data Check state, which
establishes the data plane connection and communicates the Data
Keepalive, includes the Session Identifier message element, which is
used to bind the control and data plane. Use of the Session
Identifier message element enables the AC to match the control and
data plane flows from multiple WTPs behind the same NAT system
(multiple WTPs sharing the same IP address).
In the third configuration, the AC is deployed behind a NAT. Two
issues exist in this situation. First, an AC communicates its
interfaces and corresponding WTP load using the CAPWAP Control IPv4
Address and CAPWAP Control IPv6 Address message elements. This
message element is mandatory, but contains invalid information if a
middlebox is present between the AC and WTP. The WTP MUST NOT
utilize the information in these message elements if it detects a NAT
(as described in the CAPWAP Transport Protocol message element).
Note this would disable the load balancing capabilities of the CAPWAP
protocol. Alternatively, the AC could have a configured NAT'ed
address, which it would include in either of the two control address
message elements.
The CAPWAP protocol allows for all of the AC identities supporting a
group of WTPs to be communicated through the AC List message element.
This feature MUST be ignored by the WTP when it detects the AC is
behind a middlebox.
The CAPWAP protocol allows an AC to configure a static IP address on
a WTP using the WTP Static IP Address Information message element.
This message element SHOULD NOT be used in NAT'ed environments,
unless the administrator is familiar with the internal IP addressing
scheme within the WTP's private network, and does not rely on the
public address seen by the AC.
When a WTP detects the duplicate address condition, it generates a
message to the AC, which includes the Duplicate IP Address message
element. The IP Address embedded within this message element is
different from the public IP address seen by the AC.
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-
Issue 5: Proposed text for Benefits of Using UDP-Lite? Pat Calhoun (pacalhou), October 12 2007
- Re: Issue 5: Proposed text for Benefits of Using UDP-Lite? Pat Calhoun (pacalhou), November 16 2007
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