Network Working Group L. Xue
Internet-Draft D. Guo
Intended status: Standards Track Huawei
Expires: April 27, 2015 October 24, 2014
Dynamic Stateless GRE Tunnel
draft-xue-dhc-dynamic-gre-03
Abstract
Generic Routing Encapsulation (GRE) is regarded as a popular
encapsulation tunnel technology. When a node tries to encapsulate
the user traffic in GRE, it needs the IP address of the destination
node which decapsulates the GRE packets. In practice, the GRE tunnel
destination IP address may be manually configured. This
configuration may introduce efficiency issues for operators. This
work proposes an approach to configure the GRE information
dynamically.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]
Status of This Memo
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Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. GRE Use Case - WLAN Network . . . . . . . . . . . . . . . . . 3
4. DHCP Options Definition . . . . . . . . . . . . . . . . . . . 4
4.1. GRE Discovery DHCPv4 Option . . . . . . . . . . . . . . . 4
4.2. GRE Information DHCPv4 Option . . . . . . . . . . . . . . 5
4.3. GRE Discovery DHCPv6 Option . . . . . . . . . . . . . . . 5
4.4. GRE Information DHCPv6 Option . . . . . . . . . . . . . . 6
5. Dynamic GRE Tunnel . . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
Generic Routing Encapsulation (GRE, see [RFC1701] and [RFC2784]) is
widely deployed in the operators' networks. When a node tries to
encapsulate the user traffic in a GRE tunnel, it needs the IP address
of the destination node which can decapsulate the GRE packets. In
practice, the manual configuration happens on the nodes. This may
introduce efficiency issues for operators. As an example, if GRE
tunneling is used in the access network, there may a large amount of
configuration needed at the access side. This specification
introduces a use case requiring the deployment of a large amount of
GRE tunnels, which motivates a dynamic approach. The specification
proposes a solution to enable the dynamic discovery of the GRE
decapsulation device through use of a Dynamic Host Configuration
Protocol (DHCP) option.
2. Terminology
The following terms are used in this document:
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Access Controller (AC): The network entity that provides Wireless
Termination Point (WTP) access to the network infrastructure in
the data plane, control plane, management plane, or a combination
therein.
Customer Premises Equipment (CPE): The box that a provider may
distribute to the customers. When CPE is using DHCP to obtain
network address, CPE is acting as "DHCP Client".
Wireless Termination Point (WTP): The physical or logical network
entity that contains an RF antenna and wireless physical layer
(PHY) to transmit and receive station traffic for wireless access
networks.
3. GRE Use Case - WLAN Network
Wireless Local Area Network (WLAN) has emerged as an important access
technology for service operators. A typical WLAN network contains a
large number of WTPs, centrally managed and controlled by the Access
Controller (AC). It is desirable to distribute customer data frames
to an endpoint through an Access Router (AR) different from the AC.
GRE encapsulation can be used between a WTP and an AR as one of the
optional tunneling technologies shown in
[I-D.ietf-opsawg-capwap-alt-tunnel].
An illustration of a WLAN network is shown in Figure 1. In order for
a WTP to encapsulate the user traffic in a GRE tunnel, it needs to
know the Access Router (AR) IP address. This IP address is usually
deployed on WTPs manually, which may introduce efficiency issues for
operators. An AC may dynamically configure the WTP with the AR
address via extended CAPWAP message elements (see
[I-D.ietf-opsawg-capwap-alt-tunnel]). However, this approach does
not apply to a WLAN network where the CAPWAP protocol is not
deployed, as the network shown in Figure 2. In fact, it is quite
common for operators to have their own private control plane between
the WTP and the AC rather than CAPWAP. Moreover, there are also WLAN
deployments without AC, as in the FAT WTPs scenario (see Figure 3).
A general approach to resolve this problem is desirable.
CAPWAP +--------+
++========+ AC |
// +--------+
//
+-----+// DATA Tunnel (GRE) +--------------+
| WTP |===========================| Access Router|
+-----+ +--------------+
Figure 1: GRE Use Case - WLAN Network 1
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Private Control +--------+
++========+ AC |
// +--------+
//
+-----+// DATA Tunnel (GRE) +--------------+
| WTP |===========================| Access Router|
+-----+ +--------------+
Figure 2: GRE Use Case - WLAN Network 2
+-----+ DATA Tunnel (GRE) +--------------+
| WTP |===========================| Access Router|
+-----+ +--------------+
Figure 3: GRE Use Case - WLAN Network 3
4. DHCP Options Definition
4.1. GRE Discovery DHCPv4 Option
The GRE Discovery DHCPv4 option provides to a GRE encapsulator a list
of one or more IPv4 addresses of a GRE decapsulator. According to
[RFC2131], the GRE Discovery DHCPv4 Option is structured as shown in
Figure 4.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Option Len | AR IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AR IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: GRE Discovery DHCPv4 Option
Code: TBD
Len: 4
AR IPv4 Address: AR IPv4 address, an endpoint of GRE tunnel. More
than one AR IPv4 addresses may be provided for redundancy reasons.
The default priority of the listed AR IPv4 addresses may be from
highest to lowest.
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4.2. GRE Information DHCPv4 Option
The GRE Information DHCPv4 option provides a list of the GRE
information as defined in and [RFC2784][RFC2890]. The GRE
information may include the key.
According to [RFC2131], the GRE Information DHCPv4 Option is
structured as shown in Figure 5.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Option Len | GRE Key |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GRE Key (cont.) | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: GRE Information DHCPv4 Option
Code: TBD
Len: 6
GRE Key: The Key field contains a four octet number which is inserted
by the GRE encapsulator according to [RFC2890].
Reserved: This field is reserved for future use. These bits MUST be
sent as zero and MUST be ignored on receipt.
4.3. GRE Discovery DHCPv6 Option
The GRE Discovery DHCPv6 option provides to a GRE encapsulator a list
of one or more IPv6 addresses of a GRE decapsulator. According to
[RFC7227], the GRE Discovery DHCPv6 Option is structured as shown in
Figure 6.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Option Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. AR IPv6 Address .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. AR IPv6 Address (Optional) .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: DHCPv6 GRE Discovery Option
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Code: TBD
Len: >=16
AR IPv6 Address: AR IPv6 address, an endpoint of GRE tunnel. More
than one AR IPv6 addresses may be provided for redundancy reasons.
The default priority of the listed AR IPv6 addresses may be from
highest to the lowest.
4.4. GRE Information DHCPv6 Option
The GRE Information DHCPv6 option provides a list of the GRE
information as defined in and [RFC2784][RFC2890]. The GRE
information may include the key.
According to [RFC7227], the GRE Information DHCPv6 Option is
structured as shown in Figure 7.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Option Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GRE Key |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: GRE Information DHCPv6 Option
Code: TBD
Len: 8
GRE Key: The Key field contains a four octet number which is inserted
by the GRE encapsulator according to [RFC2890].
Reserved: This field is reserved for future use. These bits MUST be
sent as zero and MUST be ignored on receipt.
5. Dynamic GRE Tunnel
The DHCP options defined in Section 4 enable an automated way to
inform the GRE encapsulator with the GRE destination IP address.
Additionally, some other GRE tunnel information may be provided. In
this way, a GRE tunnel can be setup dynamically.
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Figure 8 illustrates the procedure to set up a dynamic GRE tunnel in
the network.
/ \ IPv4-x.x.x.x IPv4-y.y.y.y / \
/ \ +-------+ +-------+ +-------+ / \
| | | | | | | | | |
| Host +-----+ CPE +-------+ DHCP +------+ AR +------+Internet
\ / | | | Server| | | \ /
\ / +-------+ +-------+ +-------+ \ /
DHCP Client DHCP Server
| | | |
| |DHCPv4 Request | |
| (1) + ------------->| |
| | | |
| | DHCPv4 Reply | |
| + <-------------| |
| | with y.y.y.y and information |
| (optional) |
| | |
| *-------------------------------*
|--------------+----User Packet-in-GRE-Encap.->|
| (2) *----with x.x.x.x -------------*
| | / \
| | | Tunnel Client |
| | \ List Config. /
| | |
| *-------------------------------*
| (3) |<-------Keepalive Packet------>|
| *-------------------------------*
Figure 8: Dynamic GRE Tunnel
The steps to set up a GRE tunnel between the CPE and the AR are as
follows:
1. The CPE, as one endpoint of GRE tunnel, sends the DHCP request
message to the DHCP server to acquire the AR access. The GRE
Discovery DHCP Option should be included, with AR IPv4 address
set to zero. When the DHCP server receives this request, it
replies to the CPE the DHCP Reply message, containing the AR
address and the tunnel information if needed.
2. The CPE can encapsulate the upstream packets from the hosts
within GRE packets. Generally, upstream packets are either data
packets or control packets. When the AR gets an encapsulated GRE
packet, the AR checks whether there is an existing GRE tunnel
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with the CPE. If this is a new endpoint without GRE record, the
AR should add this CPE into the tunnel client list.
3. A keepalive mechanism may be required for a GRE tunnel between
the CPE and the AR. If there is neither keepalive packet nor
data packet, when a keepalive timer expires, the AR or the CPE
will tear down the tunnel and release resources.
6. IANA Considerations
TBD
7. References
7.1. Normative References
[RFC1701] Hanks, S., Li, T., Farinacci, D., and P. Traina, "Generic
Routing Encapsulation (GRE)", RFC 1701, October 1994.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
2131, March 1997.
[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
March 2000.
[RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE",
RFC 2890, September 2000.
[RFC7227] Hankins, D., Mrugalski, T., Siodelski, M., Jiang, S., and
S. Krishnan, "Guidelines for Creating New DHCPv6 Options",
BCP 187, RFC 7227, May 2014.
7.2. Informative References
[I-D.ietf-opsawg-capwap-alt-tunnel]
Zhang, R., Cao, Z., Deng, H., Pazhyannur, R., Gundavelli,
S., and L. Xue, "Alternate Tunnel Encapsulation for Data
Frames in CAPWAP", draft-ietf-opsawg-capwap-alt-tunnel-03
(work in progress), September 2014.
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Authors' Addresses
Li Xue
Huawei
No. 156 Beiqing Rd. Z-park, Shi-Chuang-Ke-Ji-Shi-Fan-Yuan
Beijing, Haidian District 100095
China
Email: xueli@huawei.com
Dayong Guo
Huawei
No. 156 Beiqing Rd. Z-park, Shi-Chuang-Ke-Ji-Shi-Fan-Yuan
Beijing, Haidian District 100095
China
Email: guoseu@huawei.com
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