Internet DRAFT - draft-wang-6man-flow-label-reflection
draft-wang-6man-flow-label-reflection
Internet Engineering Task Force A. Wang
Internet-Draft China Telecom
Intended status: Standards Track S. Jiang
Expires: September 9, 2015 Huawei Technologies Co., Ltd
March 8, 2015
IPv6 Flow Label Reflection
draft-wang-6man-flow-label-reflection-01
Abstract
The current definition of the IPv6 Flow Label focuses mainly on how
the packet source forms the value of this field and how the forwarder
in-path treats it. In network operations, there are needs to
correlate an upstream session and the corresponding downstream
session together. This document propose a flow label reflection
mechanism that network devices copy the flow label value from
received packets to the corresponding flow label field in return
packets. This mechanism could simplify the network traffic
recognition process in network operations and make the policy for
both directions of traffic of one session consistent.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
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This Internet-Draft will expire on September 9, 2015.
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Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Summary of the current usage for IPv6 Flow Label . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
3. Potential Benefit of Flow Label Reflection . . . . . . . . . 4
4. Flow Label Reflection Behaviors on Network Devices . . . . . 4
5. Applicable Scenarios . . . . . . . . . . . . . . . . . . . . 5
5.1. Flow Label Reflection on CP servers . . . . . . . . . . . 5
5.2. Flow Label Reflection for Bi-direction Tunnels . . . . . 6
5.3. Flow Label Reflection on edge devices . . . . . . . . . . 7
5.4. Misc Possible Scenarios . . . . . . . . . . . . . . . . . 7
5.4.1. Aid to mitigate the ND cache DDoS Attack . . . . . . 7
5.4.2. Improve the efficiency of PTB problem solution in
load-balance environment . . . . . . . . . . . . . . 8
6. Deployment Consideration . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
The IPv6 flow label [RFC6437] in the fixed IPv6 header is designed to
differentiate the various flow session of IPv6 traffic; it can
accelerate the clarification and treatment of IPv6 traffic by the
network devices in its forwarding path. In practice, many current
implementations use the 5-tuple {dest addr, source addr, protocol,
dest port, source port} as the identifier of network flows. However,
transport-layer information, such as the port numbers, is not always
in a fixed position, since it follows any IPv6 extension headers that
may be present; in contrast, the flow label is at a fixed position in
every IPv6 packet and easier to access. In fact, the logic of
finding the transport header is always more complex for IPv6 than for
IPv4, due to the absence of an Internet Header Length field in IPv6.
Additionally, if packets are fragmented, the flow label will be
present in all fragments, but the transport header will only be in
one packet. Therefore, within the lifetime of a given transport-
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layer connection, the flow label can be a more convenient "handle"
than the port number for identifying that particular connection.
The usages of IPv6 flow label, so far as briefly summarized in
Section 1.1, only exploit the characteristic of IPv6 flow label in
one direction.
In current practice, an application session is often recognized as
two separated IP traffics, in two opposite directions. However, from
the point view of a service provider, the upstream and downstream of
one session should be handled together, particularly, when
application-aware operations are placed in the network. A ubiquitous
example is that end user initiates a request, with small-scale data
transmitted, towards a content server, then the server responds with
a large set of follow-up packets. The bi-directional flows should be
correlated together and handled with the same policy. Ideally, the
request embeds a flow recognition identifier that is accessible and
the follow-up response packets carry the same identifier. The flow
label is a good choice for the flow recognition identifier.
This document proposes a flow label reflection mechanism so that
network devices copy the flow label value from received packets to
the corresponding flow label field in return packets. By having the
same flow label value in the downstream and upstream of one IPv6
traffic session, the network traffic recognition process and the
traffic policy deployment in network operations could be simplified.
It may also increase the accuracy of network traffic recognition.
Several applicable scenarios of the IPv6 flow label reflection are
also given, in Section 5. For now, this document only considers the
scenario in a single administrative domain, although the IPv6 flow
label reflection mechanism may also bring benefits into cross domain
scenarios.
1.1. Summary of the current usage for IPv6 Flow Label
[RFC6438] describe the usage of IPv6 Flow Label for ECMP and link
aggregation in Tunnels; it mainly utilizes the random distribution
characteristic of IPv6 flow label. [RFC7098] also describes similar
usage in server farms.
All these usage scenarios consider only the usage of IPv6 flow label
in one direction, while many bi-directional network traffics need to
be treated together.
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2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119] when they appear in ALL CAPS. When these words are not in
ALL CAPS (such as "should" or "Should"), they have their usual
English meanings, and are not to be interpreted as [RFC2119] key
words.
Flow Label Reflection A mechanism/behavior so that a network device
copies the value of flow label from a IPv6 flow into a
corresponding return IPv6 flow.
Flow Label Reflection Device A network device that applies the flow
label reflection mechanism. It is the end of an IPv6 flow and the
initiation node of the corresponding return IPv6 flow.
3. Potential Benefit of Flow Label Reflection
With flow label reflection mechanism, the IPv6 Flow Label could be
used to correlate the upstream and downstream packets of bi-
directional traffics:
o It makes the downstream and upstream of one session be easily
recognized. It makes the correlation of traffic and then the
recognition of various traffics easier.
o The network operator can easily apply the same policy to the bi-
directional traffic of one interested session
o The traffic analyzer can also easily correlate the upstream and
downstream of one session to find the symptoms of various internet
protocols.
4. Flow Label Reflection Behaviors on Network Devices
To fulfill the flow label reflection mechanism, the below proposed
behaviors on network devices:
o The generation method of IPv6 flow label in source IPv6 node
SHOULD follow the guidelines in [RFC6437], that is the IPv6 flow
label should be generated randomly and distributed enough.
o On the Flow Label Reflection Device, the value of IPv6 Flow Label
from received packets SHOULD be copied into the corresponding flow
label field in return packets by the flow label reflection
devices.
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o The forwarding nodes within the management domain SHOULD follow
the specification in [RFC6437], that is the IPv6 flow label SHOULD
NOT be modified in the path, unless flow label value in arriving
packets is zero. The forwarding nodes MAY follow the
specification in [RFC6438] when using the flow label for load
balancing by equal cost multipath (ECMP) routing and for link
aggregation, particularly for IPv6-in-IPv6 tunneled traffic.
o The network traffic recognition devices, or devices that may have
differentiated operations per flow, SHOULD recognize and analyze
network traffics based on 3-tuple of {dest addr, source addr,
flowlabel}. It SHOULD consider the traffics that have same flow
label value and reversed source/dest addr as upstream and
downstream of the same flow, match them together to accomplish the
traffic recognition process.
o Other network operations MAY also be based on 3-tuple of {dest
addr, source addr, flowlabel}.
5. Applicable Scenarios
This section describes some applicable scenarios, which network
operators can benefit from deploying the flow label reflection
mechanism. It is not a complete enumeration. More scenarios may be
introduced in the future.
5.1. Flow Label Reflection on CP servers
There is rapidly increasing requirement from service providers (SP)
to cooperate with the content providers (CP) to provide more accurate
services and charging policies based on accurate traffic recognition.
The service providers need to recognize the CP/SP's bi-directional
traffics at the access edge devices of the network, such as
BRAS/PDSN/P-GW devices.
Normally, the burden for these edge devices to recognize the
subscriber's upstream traffic is light, because request messages are
typically small. But they often need more resource to recognize
downstream traffics, which normally contain large data. With flow
label reflection on CP servers, recognition based on the 3-tuple of
{dest addr, source addr, flowlabel} would reduce the consumption of
recognition and make the correlation process much easier.
In this scenario, the CP servers would be the Flow Label Reflection
Devices. They copy the flow label value from received upstream user
request packets to the corresponding flow label field in return
downstream packets.
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The access edge devices of service provider scrutinize the
subscriber's upstream IPv6 traffic and record the binding of 3-tuple
and traffic-specific policy. If the flow label is zero, the access
edge devices must rewrite the flow label value according to local
policy. With the recorded binding information, the access edge
devices can easily recognize and match the downstream packet to the
previous recognized upstream packet, by just accessing 3-tuple. The
edge devices can then apply the corresponding traffic policy to the
upstream/downstream of the session to the cooperated CP.
Note: this mechanism may not reliable when the CP servers are not
directly connected to the service provider, because there is no
guarantee the flow label would not be changed by intermediate devices
in other administrative domains.
5.2. Flow Label Reflection for Bi-direction Tunnels
Tunnel is ubiquitous within service provider networks. It is very
difficult (important if the tunnel is encrypted) for intermediate
network devices to recognize the inner encapsulated packet, although
such recognition could be very helpful in some scenarios, such as
traffic statistics, network diagnoses, etc. Furthermore, such
recognition normally requires to correlate bi-direction traffic
together. The flow label reflection mechanism could provide help in
such requirement scenarios.
In this scenario, the tunnel end devices would be the Flow Label
Reflection Devices. They record the flow label value from received
tunnel packets, and copy it to the corresponding flow label field in
return packets, which can be recognized by 5-tuple or 3-tuple of the
inner packet at the tunnel end devices.
The tunnel initiating devices should generate different flow label
values for different inner flow traffics based on their 5-tuple or
3-tuple in accordance with [RFC6437]. Note: if the inner flow is
encryption in ESP model [RFC4303], the transport-layer port numbers
are inaccessiable. In such case, 5-tuple is not available.
Then the intermediate network device can easily distinguish the
different flow within the same tunnel transport link and correlate
bi-direction traffics of same flow together. This can also increase
the service provider's traffic control capabilities.
This mechanism can also work when the encapsulated traffics are IPv4
traffics, such as DS-Lite scenario [RFC6333]. The IPv4 5-tuple may
be used as the input for the flow label generation.
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5.3. Flow Label Reflection on edge devices
If the flow label reflection mechanisms have been applied on peer
host, the service provider could always use it for bi-directional
traffic recognition. However, there is no guarantee the flow label
would not be changed by intermediate devices in other administrative
domains. Therefore, to make the flow label value trustful, the edge
devices need to validate the flow label reflection.
In this scenario, the edge devices would be the (backup) Flow Label
Reflection Devices. They record the flow label value from the
packets that leave the domain. When the corresponding flow label
field in return packets are recognized by 5-tuple or 3-tuple at the
edge devices, the edge devices should check the flow label as below:
o if the flow label matches the record value, it remains;
o if the flow label is zero, the edge devices copy the record value
into it;
o if the flow label is non-zero, but does not matches the record
value, the edge devices can decide the flow label are modified by
other intermediate devices (with the assumption the peer host has
reflect the original flow label), then restore the flow label
using the record value.
Then the network recognition devices located anywhere within the
service provider network could easily correlate bi-directional
traffics together, and apply traffic-specific policy accordingly.
5.4. Misc Possible Scenarios
In the below scenarios, the flow label reflection mechanism needs to
be combined with other mechanisms in order to achieve the design
goals.
5.4.1. Aid to mitigate the ND cache DDoS Attack
Neighbor Discovery Protocol [RFC4861][RFC4861] is vulnerable for the
possible DDoS attack to the device's ND cache, see section 11.1,
[RFC4861]. There are many proposals are aiming to mitigate this
problem, but none of them are prevalent now. It is mainly because
that there is no obvious mechanism to assure the validation of the
NS/RS packet on the first arrival, the receiving node by default will
cache the link-layer address of the NA packet. Reverse detection
mechanisms can be added to solve this issue. However, for reverse
detection mechanisms, there would be another issue: how to pair the
return NA/RA packet with the NS/RS packet on the sending node. It
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can be solved by applying the flow label reflection mechanism in the
return NA/RA packet. Then the sending node can pair the reverse
detect NS/RS packet with original NA/RA packet and response to the
reverse detect NS/RS packet correctly. Only the NS/RS packet that
passed the reverse detection validation will be accept by the node
and the link-layer address within it will be cached.
5.4.2. Improve the efficiency of PTB problem solution in load-balance
environment
[I-D.v6ops-pmtud-ecmp-problem] introduces the Packet Too Big
[RFC4443] problem in load-balance environment. The downstream packet
from a server, which responses to a client request message, may meet
a forwarding node that rejects the packet for "too big" reason. The
PTB error ICMPv6 message should be returned to the original server.
However, it requests the load balancer to distribute the PTB error
ICMPv6 message based on the information of the invoking packet within
the ICMPv6 packet, not the ICMPv6 packet itself. The load balancer
needs to obtain the source IP address and transport port information
within the invoking packet.
However, if both the server and the forwarding node that generates
the PTB message apply the flow label reflection mechanism, the PTB
error ICMPv6 message would have the same flow label with the original
client request message. Then, the load balancer, that follows
[RFC7098], could easily forward the PTB packet to same server without
parsing the transport port in the invoking packet, thus increases the
efficiency.
6. Deployment Consideration
The IPv6 flow label reflection mechanism requires the "Flow Label
Reflection Device" to be stateful, store the flow label value and
copy it to the corresponding return packet. Such change cannot be
accomplished within a short term, and therefore the deployment of
this mechanism will be accomplished gradually. During the
incremental deployment period, the traditional recognition
mechanisms, which are more expensive, would coexist. The traffics
that could not be recognized by 3-tuple of {dest addr, source addr,
flowlabel} could fall back to the traditional process or be skipped
over by advanced services. The more devices support the flow label
reflection mechanism, the less consumption for traffic recognition
from the network management perspective, or the better coverage of
advanced services that are based on the traffic recognition.
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7. Security Considerations
Security aspects of the flow label are discussed in [RFC6437]. A
malicious source or man-in-the-middle could disturb the traffic
recognition by manipulating flow labels. However, the worst case is
that fall back to the current practice that an application session is
often recognized as two separated IP traffics. The flow label does
not significantly alter this situation.
Specifically, the IPv6 flow label specification [RFC6437] states that
"stateless classifiers should not use the flow label alone to control
load distribution." This is answered by also using the source and
destination addresses with flow label.
8. IANA Considerations
This draft does not request any IANA action.
9. Acknowledgements
The authors would like to thanks Brian Carpenter, who gave many
useful advices. The authors would also like to thanks the valuable
comments made by Fred Baker, Lee Howard, Mark ZZZ Smith, Jeroen
Massar, Florent Fourcot and other members of V6OPS WG. Also, special
thanks for Florent Fourcot, who have implemented the flow label
reflection mechanims in the Linux.
This document was produced using the xml2rfc tool [RFC2629].
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
June 1999.
[RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control
Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification", RFC 4443, March 2006.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
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[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, April 2011.
[RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
"IPv6 Flow Label Specification", RFC 6437, November 2011.
[RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
for Equal Cost Multipath Routing and Link Aggregation in
Tunnels", RFC 6438, November 2011.
10.2. Informative References
[I-D.v6ops-pmtud-ecmp-problem]
Byerly, M., Hite, M., and J. Jaeggli, "Close encounters of
the ICMP type 2 kind (near misses with ICMPv6 PTB)",
draft-v6ops-pmtud-ecmp-problem-00 (work in progress),
August 2014.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
4303, December 2005.
[RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack Lite Broadband Deployments Following IPv4
Exhaustion", RFC 6333, August 2011.
[RFC7098] Carpenter, B., Jiang, S., and W. Tarreau, "Using the IPv6
Flow Label for Load Balancing in Server Farms", RFC 7098,
January 2014.
Authors' Addresses
Aijun Wang
China Telecom
Beijing Research Institute, China Telecom Cooperation Limited
No.118, Xizhimenneidajie, Xicheng District, Beijing 100035
China
Phone: 86-10-58552347
Email: wangaj@ctbri.com.cn
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Sheng Jiang
Huawei Technologies Co., Ltd
Q14, Huawei Campus, No.156 Beiqing Road
Hai-Dian District, Beijing, 100095
P.R. China
Email: jiangsheng@huawei.com
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