Internet DRAFT - draft-turaga-lmap-special-loop-address
draft-turaga-lmap-special-loop-address
Network Working Group P. Turaga
Internet-Draft R. Raszuk
Intended status: Standards Track Bloomberg LP
Expires: March 18, 2017 September 14, 2016
Special Loop Address
draft-turaga-lmap-special-loop-address-01
Abstract
This document describes a method for automatic detection of link
quality issues between two devices connected together by any standard
link in an IP based network. This document focuses on inline
detection in any network attached device (ie server, router, switch
etc..)
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].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 18, 2017.
Copyright Notice
Copyright (c) 2016 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
(http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 3
4. IPv4/IPv6 Special Purpose Loop Addresses . . . . . . . . . . 4
5. Operation of test suite using Special Purpose IP Loop Address 5
6. Comparison with stated test requirements . . . . . . . . . . 6
7. Probe size and rate calculation . . . . . . . . . . . . . . . 7
8. Probe's QOS marking . . . . . . . . . . . . . . . . . . . . . 7
9. Bandwidth Considerations for link under test . . . . . . . . 7
10. I2RS and YANG modelling . . . . . . . . . . . . . . . . . . . 7
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
12. Security Considerations . . . . . . . . . . . . . . . . . . . 8
13. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 8
14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
15.1. Normative References . . . . . . . . . . . . . . . . . . 8
15.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Terminology
o RTT - Round Trip Time
o TTL - Time to Live
o BFD - BiDirectional Failure Detection
o LFM - Link Fault Management
o ICMP - Internet Control Message Protocol
2. Introduction
Real time monitoring of WAN or MAN link quality presents a real
operational challenge. The common use of circuit emulation
techniques by carriers makes detection of the circuits degradation
difficult. Very often such reduced link quality results in increased
queuing times or packet drops beyond SLA guarantees. Furthermore,
the characteristics of link degradation is different from link to
link.
The problem space described above is further complicated due to the
following reasons:
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o Link anomalies may not occur at the same uniform rate or be of the
same constant and continuous pattern. This transient
characteristic maybe a function of load or other temporary
problems for example transport network over-subscription.
o Encountered degradated service behavior may not translate to link
errors or packet discards on either end of the suspected link
because the emulated link consisting of multiple independent L2
segments in the carrier's network.
Currently available tools on the circuit endpoints (usually routers)
do not allow easy way to diagnose circuit health. Tools used today
to detect link issues include:
o Creating hardware or software loops manually - this results in the
actual link under test to be taken out of service. Test traffic
is then sent through the link and based on the results of the
test, link quality issues are detected.
o Regular pings/probes on directly connected links between routers/
network devices - Depending on the size of the probe packets and
the rate at which they are sent between the network devices and
the loss, the link issues are detected. The issue with this
approach is that network processor on the router has to process
all these packets. This causes an additional processing load on
the routers.
o BFD, IP protocol hellos etc are based on detecting neighbor state
based on tiny and lightweight hellos. Such probes were designed
for fast detection of end-to-end link state events .. not to
evaluate link quality. If say N hellos send in T interval are
lost it is an indication about link or peer down event.
o The layer 2 OAM tools are not capable of addressing the
requirements since by definition an emulated link consists of
number of different L2 links hidden by the emulation layer and its
encapsulation. L2 OAM could only indicate potential problems
within single layer 2 link. They are light weight and some of
these issues can only be detected at various levels of data rates
(within agreed SLAs) transiting via such links.
3. Requirements
The following are some of the key considerations required to be
addressed in an alternative diagnostics solutions:
o The testing should be atomic in nature - the UUT in this document
is a single p2p link.
o The test should not be subject to any alterations by externally
injected packets
o The probe packets should never be able to transit L3 node to any
other L3 node
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o The level of diagnostics data should be configurable such that
operator is able to inject anywhere from 0.1% to 100% of test load
of a given max link capacity with build in automatic consideration
of existing average of production traffic load (unless link is
considered as taken out-of-service).
o The duration of the test traffic should be either configurable by
the operator or controlled by built-in detection heuristics.
o The frequency of the test traffic should be either configurable by
the operator or controlled by built-in detection heuristics.
o Probes should not be subject to process switching by the route
processors on either end of the link during the burst.
o The solution should strive to minimize amount of required protocol
extensions for as easy as possible inter-operability
characteristics.
o In the topologies where Link Aggregation is used, the aggregated
bandwidth of the link should be considered instead of the
individual links. The probe accounting should be recorded as
total of all link members. Probe's hashing should follow normal
data plane load balancing rules as configured on the directly
connected peering routers.
4. IPv4/IPv6 Special Purpose Loop Addresses
The mechanism for the set of proposed requirements can be constructed
by combining two standards based protocol elements: TTL field
processing and special purpose IPv4 or IPv6 loop addresses.
Special purpose loop address will allow to setup a scoped link based
loop and TTL field can be used to limit the loop duration.
The special purpose loop address for this purpose can be subset of
the link local range - 169.254/16 for IPv4 [RFC 3927] or FE80::/64
for IPv6 [RFC 4291] or it could be taken from an alternative pool if
IETF process suggests so. Selected and allocated special purpose
loop address would be therefor kept and maintained by IANA IPv4 or
IPv6 Special-Purpose Address Registries.
Routers must not forward any packets with loop source or destination
addresses to links other then the link packet arrived on.
The IPv4/IPv6 loop address MAY BE associated with numbered IP
addresses for the given link or with link local addresses. The
resolution to MAC address of L2 rewrites would be resolved locally
through corresponding L3 adjacency addresses.
IPv4/IPv6 test packet is directed towards L3 neighbor with even TTL
value.
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5. Operation of test suite using Special Purpose IP Loop Address
The following is considered as a high level description of proposed
solution:
o Two routers R1 and R2 connected together by link L1
o Average RTT between R1 and R2 on link L1 is 5ms
o R1 and R2 have IP connectivity with each other on 10.10.10.0/30
numbered link. R1 has been configured with IP an address of
10.10.10.1 and R2 has been configured with an IP address of
10.10.10.2
o For the purpose of a test an IP loop address is configured on R1
and R2 to create local link loops. For the purpose of this
illustration the loop address has been named as L.O.O.P/32
The following IPv4 packet has been injected from R1:
o Source IP address: 10.10.10.1
o Destination IP address: L.O.O.P
o TTL = 254
o payload optional ... (to be discussed by WG)
Test sequence:
o Packet arrives at R2 and TTL is decremented following by
destination IP lookup and re-injection towards R1
o Packet keeps looping till the TTL expires on R1.
o Upon TTL expiration an ICMP TTL EXPIRED error message is being
sent to the source of the original packet (10.10.10.1). The ICMP
message contains the header information of the original packet
Observations:
o A test probe packet has been amplified 254 times for a short time
o An ICMP TTL expired message is indicative that result of the test
can be described as: probe packets were not dropped
o No ICMP TTL message implies that one copy of the original packet
was lost while it was looping between two routers. No reception
of ICMP TTL indicates potential issues with the link provided that
test sequence was assured never exceed agreed SLAs for a given
link.
o Ability to send multiple packets of different sizes on the link
with inherently controlled TTL loop can results in expected burst
of control/probe traffic on the link under test
o Such probe burst can be programmed to get to a certain % of the
link speed for a short time
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Based on fine tuned testing scenario allowing to fill the bandwidth
up to a certain % of link capacity the count of packets originally
sent by router R1 should be the same as the number of ICMP TTL
expired messages. If the count of packets originally sent by router
is the same as the number of ICMP TTL expired messages then the test
is successful. If however the number of ICMP TTL expired messages is
less than the count of packets originally sent by the router then the
test is unsuccessful proving potential problems with the link.
A test probe packet with even initial TTL value will generate a TTL
time expired ICMP message on the originating router. A test probe
packet with odd initial TTL value will generate a TTL time expired
ICMP message on the neighboring router. It is RECOMMENDED that the
test probe is sent with even initial TTL value. So, ICMP messages
are not traversing the link under test.
It is RECOMMENDED that a special payload structure is used for these
test probes with sequence numbers. When the TTL expires and an ICMP
message is generated, the IP header + 64 bits from original packet
gets copied to ICMP message [RFC792]. This can be used for
associating the ICMP message and the test.
The MTU of the test probes can be adjusted up to maximum MTU value of
the link. Fragmentation of probe packets SHOULD be avoided.
6. Comparison with stated test requirements
Analysis of the proposed solution against the actual new test
methodology requirements:
o Provides means to potentially fill up the part of link bandwidth
very rapidly due to inherent amplification especially with high
initial TTL value. The fill level of the test traffic is a
function of: Initial packet size (higher the packet size the
higher the fill level), Initial TTL value (higher the TTL value,
higher the multiplicative factor for packets and hence higher the
fill level), Initial number of packets sent (the more the packets
sent the more the fill level) and MTU of the probe packets.
o Test can be run together with production traffic. There is no
impact on production traffic neither there is any requirement to
stop production traffic in order to perform the test.
o The amplification of the packets and looping happens as a part of
inherent forwarding in the routers. This solution does not
require a special process in software or hardware to send the test
probes between the two routers as special purpose loop address
would be part of standard FIB tables.
o This mechanism is light-weight and does not require any new
software implementations. Potential for local vendor's
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optimizations however is still there in the area of segmenting TTL
equal zero errors of probes from other transit uses of TTL equal
zero errors or in the space of result presentation to the
operators.
7. Probe size and rate calculation
Initial packet size and rate are important to determine the test fill
level for the link. The test packet loops the same number of times
as the original TTL value of the original packet. The time it takes
for the original packet to come back to the original router is the
RTT (Round Trip Time) value between two routers.
Under the assumptions that: RTT of link under test is 1ms, link speed
1 Gb/s, packet size of test packet is 1536 bytes, TTL on original
packet is set to 254, would result in the test packets looping for
254 ms.
Under the above assumptions it is easy to calculate that in order
fill 1 Gb/s link to 100% 81 such probe packets need to be injected.
Likewise in order to fill such link to 20% of its capacity 16 probe
packets are required.
8. Probe's QOS marking
Since injected test packets are regular IP packets they can be marked
with any class of service. As a result the test probes similar to
actual data will be processed based on the real QoS configuration and
will be subject to treatment defined for a given packet class.
That allows both prioritization as well as de-prioritization of a
given set of test probes.
9. Bandwidth Considerations for link under test
The payload of the test packets can be of any IP protocol.
The link fill levels is also a function of Inter-packet gap of the
test and the RTT of that link. Deterministic fill levels can only be
derived by accounting for RTT of the link under test.
10. I2RS and YANG modelling
It is expected that link testing methodology described in this
document will be accessible by I2RS channel as well as extensions to
YANG models will be defined for both setting and retrieval of the
data.
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11. IANA Considerations
This document requires IANA to allocate and maintain following
Special Purpose IP Addresses:
IPv4 Special Purpose Loop Address and maintain it the IANA IPv4
Special-Purpose Address Registry [RFC5735]
IPv6 Special Purpose Loop Address and maintain it the IANA IPv6
Special-Purpose Address Registry [RFC5156]
12. Security Considerations
While the proposed mechanism does not define any new protocols nor
protocol extensions of already existing specifications it does relay
on the TTL-expiry notifications.
Such notifications must be enabled and must not be limited in any way
for the specific class of probe packets.
It is highly recommended that test destinations LOOP addresses are
not routeable beyond their locally attached links. Using IPv4/IPv6
special purpose loop addresses will address that.
13. Contributors
Authors would like to thank Truman Boyes and Leo Pang for their
valuable input.
14. Acknowledgments
15. References
15.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC5156] Blanchet, M., "Special-Use IPv6 Addresses", RFC 5156,
DOI 10.17487/RFC5156, April 2008,
<http://www.rfc-editor.org/info/rfc5156>.
[RFC5735] Cotton, M. and L. Vegoda, "Special Use IPv4 Addresses",
RFC 5735, DOI 10.17487/RFC5735, January 2010,
<http://www.rfc-editor.org/info/rfc5735>.
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15.2. Informative References
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, DOI 10.17487/RFC0792, September 1981,
<http://www.rfc-editor.org/info/rfc792>.
[RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
Configuration of IPv4 Link-Local Addresses", RFC 3927,
DOI 10.17487/RFC3927, May 2005,
<http://www.rfc-editor.org/info/rfc3927>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <http://www.rfc-editor.org/info/rfc4291>.
Authors' Addresses
Partha Turaga
Bloomberg LP
731 Lexington Ave
New York City, NY 10022
USA
Email: pturaga@bloomberg.net
Robert Raszuk
Bloomberg LP
731 Lexington Ave
New York City, NY 10022
USA
Email: robert@raszuk.net
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