Internet DRAFT - draft-tsou-bfd-ds-lite
draft-tsou-bfd-ds-lite
Internet Engineering Task Force T. Tsou, Ed.
Internet-Draft Huawei Technologies (USA)
Intended status: Informational March 23, 2012
Expires: September 24, 2012
BFD Support DS-Lite
draft-tsou-bfd-ds-lite-02
Abstract
In DS-Lite, the tunnel is not associated with any state information,
which makes it difficult to manage and diagnose. Some tools may be
used to resolve this problem.
Status of this Memo
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This Internet-Draft will expire on September 24, 2012.
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Table of Contents
1. Problem statement . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. BFD . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1.1. DS-Lite Scenario . . . . . . . . . . . . . . . . . . . 4
3.1.2. Parameters for BFD . . . . . . . . . . . . . . . . . . 4
3.1.3. Procedures . . . . . . . . . . . . . . . . . . . . . . 5
3.1.4. Implementation Considerations . . . . . . . . . . . . . 5
3.2. PCP . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.3. PING . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Failover . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8
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1. Problem statement
In DS-Lite [RFC6333], the IPv4-in-IPv6 tunnel is stateless, no status
information about tunnel is available, and no keep-alive mechanism is
available. It is difficult to know whether the tunnle is up or down,
which creates a problem for operation and maintenance.
If a B4 can detect a failure in the link to AFTR, it can switch to
another AFTR, setup new tunnel to that AFTR, so as to continue the
network service. Anycast could be used for the same purpose --
failover, but there is an ICMP error message problem, that is, when a
packet is sent from AFTR to B4, one of the routers along the path may
generate an error ICMP message, e.g., packet too big, and the error
message is not sent back to the source AFTR, but sent to another
AFTR.
In some cases, the operators may want to have some more diagnostic
functions besides connectivity test, e.g. delay and throughput test,
this may be useful if the operator is providing services like IPTV
and video conference. ETHOAM and BFD can provide these
functionalities. But ETHOAM[802.1ag - 2007]is for ethernet layer2;
and BFD OAM functions now is only available for MPLS-TP[RFC6374].
This is currently out of the scope of this spec.
1.1. 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 RFC 2119 [RFC2119].
2. Terminology
AFTR: Address Family Transition Router.
B4: Basic Bridging BroadBand.
BFD: Bidirectional Forwarding Detection.
CPE: Customer Premise Equipment (i.e., the DS-Lite B4).
FQDN Fully Qualified Domain Name.
PCP Port Control Protocol.
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3. Solutions
3.1. BFD
BFD is a mechanism intended to detect faults in the bidirectional
path. It is usually used in conjunction with applications like OSPF,
IS-IS, etc, for fast fault recovery/fast re-route. [RFC5882]
BFD [RFC5880]can be used in DS-Lite, by creating a BFD session
between the B4 and the AFTR to provide tunnel status information. If
a fault is detected the B4 can try to create a DS-Lite tunnel with
another AFTR and terminate the existing one, so as to continue
network service.
[I-D.vinokour-bfd-dhcp]proposes using a DHCP option to distribute BFD
parameters to the B4. But in case of DS-Lite, some of the key BFD
parameters are already available (e.g., peer IP address is already
available), and other parameters can be negotiated by BFD signaling
or statically configured, so that no extra DHCP option(s) need to be
defined.
3.1.1. DS-Lite Scenario
In DS-Lite [RFC6333], the BFD packet SHOULD be sent through an IPv4-
in-IPv6 tunnel, as shown in Figure 1. The IPv4 addresses of the B4
and AFTR SHOULD be the endpoints of a BFD session.
+--------------+ +--------------+
+------+ | | +------+ | |
| |-----+--------------+-----| | | |
| CPE | IPv6 Tunnel | AFTR |-----| IPv4 Network |
| (B4) |-----+--------------+-----| | | |
+------+ | IPv6 Network | +------+ | |
192.0.0.2 +--------------+ 192.0.0.1 +--------------+
Figure 1: DS-Lite Scenario
3.1.2. Parameters for BFD
In order to set up a BFD session, the following parameters are
needed, as shown in Section 4.1 of[RFC5880]:
o Peer IP address
o My Discriminator
o Your Discriminator
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o Desired Min TX Interval
o Required Min RX Interval
o Required Min Echo RX Interval
In DS-Lite [RFC6334], the B4 WAN-side IPv4 address is a well-known
address 192.0.0.2, and the AFTR's IPv4 address is 192.0.0.1, as
defined in section 5.7 of[RFC6333]. Because all the B4s and AFTRs
use the same well-known IP addresses, IPv4 addresses are not
sufficient for setting up a BFD session. From the B4's point of
view, the B4 needs to create an IPv6 tunnel to an AFTR so as to get
network connectivity to the AFTR, and send IPv4 BFD packets through
the tunnel to manage it.
The other parameters listed above can be negotiated by BFD signaling,
and initial values can be configured on the B4 and AFTR.
3.1.3. Procedures
In DS-Lite [RFC6333], when a B4 gets online, it will be assigned an
IPv6 prefix/address, and also the FQDN of the AFTR, as defined in
[RFC6334]. The B4 will create an IPv6 tunnel to the AFTR with which,
along with the well known B4 IPv4 address 192.0.0.2 and AFTR IPv4
address 192.0.0.1, the B4 can initiate a BFD session to the AFTR.
BFD packets will be sent through DS-Lite tunnel. As defined in
section 4 of [RFC5881], BFD control packet MUST be sent in UDP packet
with destination port 3784, and BFD echo packet MUST be sent in UDP
packet with destination port 3785.
When sending out the first BFD packet, the B4 can generate a unique
local discriminator, and set the remote discriminator to zero. When
the AFTR receive the first BFD packet from a B4, the AFTR will also
generate a corresponding local discriminator, and put it in the
response packet to the B4. This will finish the discriminator
negotiation in the B4 to AFTR direction, without any manual
configuration.
When the AFTR receives the first packet from a B4, AFTR will get the
IPv6 address and discriminator of the B4, so that the AFTR can
initiate the BFD session in the other direction and a similar
discriminator negotiation can be carried out.
3.1.4. Implementation Considerations
BFD is usually used for quick fault detection, at a very small time
scale, e.g. milliseconds. But in DS-Lite, it may not be necessary to
detect faults in such a short time. On the other hand, an AFTR may
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need to support tens of thousands of B4s, which means the AFTR will
need to support the same number of BFD sessions. In order to meet
performance requirements on the AFTR, it may be necessary to extend
the time period between BFD packet transmissions to a longer time,
e.g., 10s or 30s.
3.2. PCP
PCP [I-D.ietf-pcp-base-23] is a NAT traversal tool, and it can also
be used for network connectivity test if PCP is supported in the
network. A common use case of PCP is to create pinhole so that
external users can visit the serviers located behind a NAT, and the
lifetime of the pinhole mapping is usually long, e.g. hours, and the
lifetime will be refreshed periodically by the client before it is
expired. For the purpose of network connectivity test, B4 can create
a mapping in the CGN via PCP, with short life time, e.g. 10s of
seconds, and keep on refreshing the mapping before it is expired. If
any refresh request fail, B4 knows that something is wrong with the
link or the PCP server or CGN.
In order to detect the network connectivity of the DS-Lite tunnel,
the encapsulation mode MUST be used for PCP -- PCP packets are sent
through DS-Lite tunnel. Encapsulation mode and plain mode are two
alternatives for PCP, there is no concensus yet which one should be
prefered in the PCP spec.
3.3. PING
PING is a common tool used for network node reachability tes, most of
the network nodes provide this tool. In case of DS-Lite, B4 can send
PING packets to AFTR periodically. If B4 does not receive response
packets for a certain number of PING request packet, e.g. 3, then B4
decides that a fault is detected.
In order to test the connectivity of DS-Lite tunnel, PING packets
MUST be sent using ICMPv4, rather than ICMPv6.
BFD can provide more diagnostic functions than PING, as depicted in
section 4.1 of [RFC5880].
4. Failover
The FQDN of the AFTR is sent to B4 via a DHCP option, as defined in
[RFC6334]. Multiple IP addresses can be configured for an FQDN on
the DNS server. If B4 detect a failure on the link to AFTR, B4 MUST
terminate the current DS-Lite tunnel, choose another AFTR address in
the list, and create a tunnel to the new AFTR. B4 SHOULD also re-
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configure the connectivity test tool accordingly if necessary, and
restart the test procedures.
5. IANA Considerations
This memo includes no request to IANA.
6. Security Considerations
In DS-Lite [RFC6333], the B4 may not be directly connected to the
AFTR; there may be other routers between them. Then there are
potential spoofing problems, as described in [RFC5883]. Hence
cryptographic authentication SHOULD be used as described in [RFC5880]
if security is concerned.
7. Acknowledgements
The author would like to thank Mohamed Boucadair for his useful
comments, more solutions are included in this memo.
8. References
8.1. Normative References
[I-D.ietf-pcp-base-23]
Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
Selkirk, "Port Control Protocol (PCP)(work in progress)",
Feb 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, June 2010.
[RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
June 2010.
[RFC5882] Katz, D. and D. Ward, "Generic Application of
Bidirectional Forwarding Detection (BFD)", RFC 5882,
June 2010.
[RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
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(BFD) for Multihop Paths", RFC 5883, June 2010.
[RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack Lite Broadband Deployments Following IPv4
Exhaustion", RFC 6333, August 2011.
[RFC6334] Hankins, D. and T. Mrugalski, "Dynamic Host Configuration
Protocol for IPv6 (DHCPv6) Option for Dual-Stack Lite",
RFC 6334, August 2011.
[RFC6374] Frost, D. and S. Bryant, "Packet Loss and Delay
Measurement for MPLS Networks", RFC 6374, September 2011.
8.2. Informative References
[802.1ag - 2007]
IEEE Computer Societ, "IEEE Standard for Local and
Metropolitan Area Networks - Virtual Bridged Local Area
Networks Amendment 5: Connectivity Fault Management",
2007.
[I-D.vinokour-bfd-dhcp]
Vinokour, V., "Configuring BFD with DHCP and Other
Musings", May 2008.
Author's Address
Tina Tsou (editor)
Huawei Technologies (USA)
2330 Central Expressway
Santa Clara CA 95050
USA
Phone: +1 408 330 4424
Email: tina.tsou.zouting@huawei.com
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