HOMENET IS-IS and Babel Comparison
draft-mrw-homenet-rtg-comparison-00
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| Last updated | 2015-02-09 | ||
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draft-mrw-homenet-rtg-comparison-00
Homenet Working Group M. Wasserman
Internet-Draft Painless Security
Intended status: Standards Track C. Hopps
Expires: August 13, 2015 Deutsche Telekom
J. Chroboczek
University of Paris-Diderot (Paris 7)
February 9, 2015
HOMENET IS-IS and Babel Comparison
draft-mrw-homenet-rtg-comparison-00.txt
Abstract
This document is intended to provide information to members of the
IETF Home Networks Working Group (HOMENET WG), so that we can make an
informed decision regarding which routing protocol to use in home
networks. The routing protocols compared in this document are: The
Babel Routing Protocol (Babel) and The Intermediate System to
Intermediate System Intra-Domain Routing Protocol (IS-IS).
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
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 13, 2015.
Copyright Notice
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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Protocols and Extensions Included in Comparison . . . . . . . 3
2.1. IS-IS Protocol and Extensions . . . . . . . . . . . . . . 3
2.2. Babel Protocol and Extensions . . . . . . . . . . . . . . 4
3. Routing Algorithms . . . . . . . . . . . . . . . . . . . . . 4
3.1. Link State Algorithm . . . . . . . . . . . . . . . . . . 4
3.2. Distance-Vector Algorithm (Babel) . . . . . . . . . . . . 4
3.3. Algorithm Comparison . . . . . . . . . . . . . . . . . . 4
4. Support for Source-Specific Routing . . . . . . . . . . . . . 5
4.1. Source Specific Routing in IS-IS . . . . . . . . . . . . 5
4.2. Source Specific Routing in Babel . . . . . . . . . . . . 5
4.3. Discussion . . . . . . . . . . . . . . . . . . . . . . . 5
5. Support for Link Metrics . . . . . . . . . . . . . . . . . . 6
5.1. Link Metrics in IS-IS . . . . . . . . . . . . . . . . . . 6
5.2. Link Metrics in Babel . . . . . . . . . . . . . . . . . . 6
6. Support for Attached Stub Networks . . . . . . . . . . . . . 6
6.1. IS-IS Support for Stub Networks . . . . . . . . . . . . . 6
6.2. Babel Supportt for Stub Networks . . . . . . . . . . . . 6
7. Security Features . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Security Features in IS-IS . . . . . . . . . . . . . . . 6
7.2. Security Features in Babel . . . . . . . . . . . . . . . 7
8. Support for Multicast . . . . . . . . . . . . . . . . . . . . 7
8.1. Multicast Routing in IS-IS . . . . . . . . . . . . . . . 7
8.2. Multicast Routing in Babel . . . . . . . . . . . . . . . 7
9. Implementation Status . . . . . . . . . . . . . . . . . . . . 7
10. Code and State Size . . . . . . . . . . . . . . . . . . . . . 7
10.1. IS-IS Code and State Size . . . . . . . . . . . . . . . 7
10.2. Babel Code and State Size . . . . . . . . . . . . . . . 8
11. Scalablity on IEEE 802.11 Wireless Networks . . . . . . . . . 9
11.1. IS-IS Scalability on 802.11 . . . . . . . . . . . . . . 9
11.2. Babel Scalability on 802.11 . . . . . . . . . . . . . . 9
12. Standardization Status . . . . . . . . . . . . . . . . . . . 9
12.1. IS-IS Standardization . . . . . . . . . . . . . . . . . 9
12.2. Babel Standardization Status . . . . . . . . . . . . . . 10
13. Evaluation of RFC 5218 Criteria . . . . . . . . . . . . . . . 10
13.1. Critical Success Factors . . . . . . . . . . . . . . . . 10
13.1.1. IS-IS Success Factors . . . . . . . . . . . . . . . 10
13.1.2. Babel Success Factos . . . . . . . . . . . . . . . . 11
13.2. Willing Implementors . . . . . . . . . . . . . . . . . . 11
13.2.1. IS-IS . . . . . . . . . . . . . . . . . . . . . . . 11
13.2.2. Babel . . . . . . . . . . . . . . . . . . . . . . . 12
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13.3. Willing Customers . . . . . . . . . . . . . . . . . . . 12
13.3.1. IS-IS . . . . . . . . . . . . . . . . . . . . . . . 12
13.3.2. Babel . . . . . . . . . . . . . . . . . . . . . . . 12
13.4. Potential Niches . . . . . . . . . . . . . . . . . . . . 12
13.4.1. IS-IS . . . . . . . . . . . . . . . . . . . . . . . 12
13.4.2. Babel . . . . . . . . . . . . . . . . . . . . . . . 12
13.5. Complexity Removal . . . . . . . . . . . . . . . . . . . 13
13.5.1. IS-IS . . . . . . . . . . . . . . . . . . . . . . . 13
13.5.2. Babel . . . . . . . . . . . . . . . . . . . . . . . 13
13.6. Killer App . . . . . . . . . . . . . . . . . . . . . . . 13
13.6.1. IS-IS . . . . . . . . . . . . . . . . . . . . . . . 13
13.6.2. Babel . . . . . . . . . . . . . . . . . . . . . . . 13
13.7. Extensible . . . . . . . . . . . . . . . . . . . . . . . 13
13.7.1. IS-IS . . . . . . . . . . . . . . . . . . . . . . . 14
13.7.2. Babel . . . . . . . . . . . . . . . . . . . . . . . 14
13.8. Success Predictable . . . . . . . . . . . . . . . . . . 14
13.8.1. IS-IS . . . . . . . . . . . . . . . . . . . . . . . 14
13.8.2. Babel . . . . . . . . . . . . . . . . . . . . . . . 14
14. Informative References . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
This document compares IS-IS (ISO/IEC 10589:2002) [RFC1142] and Babel
[RFC6126] across several criteria related to their use in home
networks, as defined by the HOMENET WG (HOMENETs).
Although there are substantial differences between the IS-IS and
Babel routing protocols, both routing protocols work well, and either
of them could be used in a home network. There are many
characteristics of these protocols that make them more or less
suitable for use in HOMENETs, as defined in (reference homenet
architecture and HNCP documents), and those characteristics are
explored in this document.
2. Protocols and Extensions Included in Comparison
Both IS-IS and Babel are living protocols that are updated and
extended over time. This section lists the extensions that were
considered in this comparison. Additional protocol extensions could
affect some of the information included in this document.
2.1. IS-IS Protocol and Extensions
In addition to the base IS-IS protocol specification (ISO/IEC
10589:2002), this comparison considers the following IS-IS
extensions:
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2.2. Babel Protocol and Extensions
In addition to the base Babel Protocol specification (RFC 6126), this
comparison considers the following Babel extensions:
Source-Specific Routing [BABEL-SS], described in more detail in
[SS-ROUTING].
Extension Mechanism for the Babel Routing Protocol[BABEL-EXT]
3. Routing Algorithms
IS-IS is a Link State routing protocol, and Babel is a Loop-avoiding
Distance Vector routing protocol. There are some differences between
these algorithms, particularly in terms of scalability, how much
information is exchanged when the routing topology changes, and how
far topology changes are propagated. [chopps: Perhaps we should see
if we can find an external reference for comparing DVRP to link-state
RPs for this section].
3.1. Link State Algorithm
Link state algorithms distribute information for each node to compute
a tree representing the entire network.
Link state algorithms scale well in both very large and very dense
networks.
3.2. Distance-Vector Algorithm (Babel)
Distance-vector algorithms distribute information about the path
length to reach each destination through a given neighbor. Packets
are forwarded to the neighbor who is advertising the shortest path to
reach the destination.
3.3. Algorithm Comparison
Loop-avoiding Distance Vector scales beautifully to very large
networks -- the amount of state is linear in the number of nodes, and
does not need to be propagated in a timely manner. It scales badly
in extremely dense deployments, where a single node has thousands of
direct neighbours; such deployments are unlikely, and clearly outside
the scope of Homenet.
Naive link state has somewhat worse scaling properties, since it has
state that is proportional to the number of edges in the network
graph, and requires strict state synchronisation between nodes.
Real-world link-state protocols work around that issue by splitting
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the network into multiple "areas", and performing distance-vector
routing between areas. It is unclear whether this workaround is
suitable for Homenet.
4. Support for Source-Specific Routing
Source-Specific Routing is a hard requirement for HOMENETs, as it
will allow traffic to be routed to the correct outbound network based
on host source address selection. Routing packets to the wrong
outbound network could result in packets being dropped due to ISP
ingress filtering rules.
Both Babel and IS-IS have extensions for source-specific routing.
4.1. Source Specific Routing in IS-IS
[XXX: chopps]
Reports indicate that IS-IS has critical issues (routing loops) in a
mixed environment where some routers support Source-Specific Routing,
and some routers do not. However, this is not likely to be a problem
for Homenet, as we will require Source-Specific Routing on all
routers.
4.2. Source Specific Routing in Babel
The Source-specific extension to the Babel routing protocol
[BABEL-SS] has been implemented for over a year, has been made widely
available and has seen a fair amount deployment as part of OpenWRT
and CeroWRT. The implementation is currently being merged into the
standard Babel implementation, and is scheduled to be included in
version 1.6 (planned for March 2015).
4.3. Discussion
Babel's source-specific extensions were carefully designed so that
source-specific and ordinary (non-specific) routers can coexist in a
single routing domain, without routing pathologies such as routing
loops. Interoperability between plain Babel and Source-Specific
Babel is described in detail in Section VI.A of [SS-ROUTING].
Reports indicate that source-specific IS-IS has critical issues
(routing loops) in a mixed environment where some routers support
Source-Specific Routing, and some routers do not. However, this is
not likely to be a problem for Homenet, as we will require Source-
Specific Routing on all routers.
[How will we enforce that? -- jch]
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5. Support for Link Metrics
5.1. Link Metrics in IS-IS
IS-IS supports 2 types of link metrics a legacy link metric (which
should probably not be considered for HOMENET use) and a modern
extended (24-bit) link metric. Additionally multi-topology support
allows for a variable number of metrics per link.
5.2. Link Metrics in Babel
In Babel, metrics are unsigned 16-bit integers, which means that
metrics are arbitrary integers between 0 and 65534 (the value 65535
is reserved to mean "infinity"); this has been found to be sufficient
even in the chaotic environment of wireless mesh networks. If
needed, the Babel extension mechanism can be used to extend the
metric space in arbitrary ways (not just integers), which has already
been done by the radio interference extensions to Babel [BABEL-Z].
6. Support for Attached Stub Networks
[I don't understand why this issue is important for Homenet. -- jch]
6.1. IS-IS Support for Stub Networks
A stub network in IS-IS is supported by the advertisement of
reachability to a prefix by a router in its LSP. [How does this
prevent the network from being used for transit? -- jch]
6.2. Babel Supportt for Stub Networks
Babel supports flexible filtering of routes, and a stub network can
be designated by simply setting up the necessary filtering rules.
For resource-limited deployments, a minimalistic, stub-only
implementation of Babel is available.
7. Security Features
7.1. Security Features in IS-IS
IS-IS offers multiple levels of security from none, to simple clear-
text (password) authentication, to fully generic cryptographic
authentication using any number of hashing algorithms (e.g., HMAC-
MD5, HMAC-SHA1, ... HMAC-SHA512) based on security associations
(link, area and domain scoped).
[What does that mean? Just support for HMAC-based authentication, or
am I missing something? -- jch]
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7.2. Security Features in Babel
Babel supports an extensible HMAC-based cryptographic authentication
mechanism [RFC7298].
8. Support for Multicast
Although the HOMENET WG has not yet determined how/if to support
multicast in HOMENET Networks, it might be desirable to pick a
routing protocol that supports multicast, so that it will be easier
to add multicast support in the future.
8.1. Multicast Routing in IS-IS
The IS-IS protocol supports multicast routing. However, none of the
available implementations include support for multicast. [XXX:
chopps: what do we mean by supporting multicast routing?]
[Does the Homenet implementation support multicast? Does any open
source implementation support multicast? -- jch]
8.2. Multicast Routing in Babel
There is no support for multicast routing in Babel.
9. Implementation Status
There are Homenet implementations of both IS-IS and Babel.
Only the Homenet implementation of IS-IS supports source-specific
routing, which is a hard requirement for Homenet. If source-specific
routing is not required, there are several independent, interoperable
implementations of IS-IS (all major router vendors implement IS-IS),
including some open source implementations.
There are multiple open source implementations of Babel, two of which
support source-specific routing. However, they were both originally
derived from the same codebase.
10. Code and State Size
10.1. IS-IS Code and State Size
The Homenet implementation of IS-IS consists of 7000 lines of Erlang
code and has an installed size of over 11MB. Its initial memory
usage (as reported by the operating system) is 22MB, and its working
set increases by XXX bytes for each new edge in the network graph.
To put these numbers into perspective, in a network with XXX nodes
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each of which has XXX neighbours, the Homenet implementation of IS-IS
requires XXX bytes for its data structures.
[I suggest removing the rest of this section, since it consists of
unsubstantiated, vague claims depending on a not-yet-implemented
version of a not-yet-specified subset of a large protocol. -- jch]
The code size of IS-IS depends greatly on what aspects of the
protocol have been implemented. IS-IS supports multiple address
families as well as completely different protocol stacks (OSI and
IP), multiple area hierachical operation with automatic virtual link
support for repairing area partitions, and multiple link types.
Additionally many other protocol features have been added over time
to augment the protocol or replace previous behavior. The protocol
lends itself well to not only extension, but pairing down of
features.
For HOMENET we could use a very simple level-2 only implementation
supporting a common topology supporting IPv4 and IPv6 over broadcast
(i.e., ethernet) link types. Additionally, we would need only
support the latest extended metric TLV (i.e., not implement legacy
metric support). Implemented as such the code size should be very
manageable.
The state actually required by IS-IS is not large, and primarily
correlates to the number of routers in the network (for LSP storage).
The protocol stores it's own link and adjacency data which is
expected to be negligible. Additionally, the protocol stores
received and generated LSPs, and typically an SPF tree with prefix
information attached. This state correlates directly to the number
of routers and prefixes in the network. Each router in the network
generates, a single LSP (possibly fragmented into segments) with
prefix information, a single copy of these LSPs is stored by each
router in the network regardless of the number of links, adjacencies
or the distance (or number of hops) from the storing router to the
advertising router.
10.2. Babel Code and State Size
The source-specific implementation of Babel, which implements many
non-Homenet extensions to the protocol, consists of roughly 10000
lines of C and has an installed size of less than 130kB on AMD-64.
Its initial memory usage (as reported by the operating system) is
300kB.
The amount of state stored by a Babel router is at worst one routing
table entry for each destination through each neighbour. In the
source-specific implementation, one routing entry occupies roughly
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100 bytes of memory. To put these figures into perspective, in a
network with 1000 nodes, a Babel router with 10 neighbours needs
roughly a megabyte of memory to store its routing table (not counting
malloc overhead).
The stub-only implementation of Babel consists of 900 lines of C and
compiles to 12kB (dynamically linked). Its memory usage (as reported
by the operating system) is 200kB, and remains constant (it doesn't
perform any dynamic memory allocation).
11. Scalablity on IEEE 802.11 Wireless Networks
[I suggest renaming this section to "Performance on 802.11 wireless
networks. Are we trying to get homenets to scale to millions of
nodes? -- jch]
11.1. IS-IS Scalability on 802.11
IS-IS is in active use in in the Internet in large non-hierachical
(i.e., level-2 or single area level-1) deployments with hundreds of
nodes. The protocol has proven to be very scalable.
Do we have any information about the scaling of IS-IS on 802.11
networks, in particular?
11.2. Babel Scalability on 802.11
Babel was carefully optimised for 802.11 networks. In particular, it
has (optional) provisions for link quality estimation and (optional)
provisions for radio-interference sensitive routing.
Babel was designed to work well on pure mesh networks (networks where
a packet might exit through the same interface as the one it came
from), but this is probably out of scope for Homenet.
12. Standardization Status
12.1. IS-IS Standardization
IS-IS is an ISO Standard documented in ISO/IEC 10589:2002. There is
an active IETF IS-IS Working Group (ISIS) that maintains and extends
the IS-IS protocol, and the IS-IS protocol has been extended in
several ISIS Working Group documents.
The source-specific extension to IS-IS is standardized as XXX. [Will
it require a downref? -- jch]
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12.2. Babel Standardization Status
Babel is documented in an Experimental RFC (RFC 6126) published in
2011, and it has been updated in several individual-submission RFCs
and Internet Drafts.
The use of Babel in a Standards Track HOMENET RFC would require a
"downref" to non-Standards Track documents. It would also be
necessary to publish the extensions that are needed for the HOMENET
use case as RFCs.
13. Evaluation of RFC 5218 Criteria
13.1. Critical Success Factors
Does the protocol exhibit one or more of the critical initial success
factors as defined in RFC 5218?
13.1.1. IS-IS Success Factors
IS-IS exhibits the following critical initial success factors:
Positive Net Value:
Hardware cost: None.
Operational interface: Existing and extensive.
Retraining: None.
Business dependencies: None.
Incremental Deployment: Yes.
Open Code Availability: Yes. Multiple implementations.
Freedom from Usage Restrictions: Yes.
Open Specification Availability: Yes.
Open Maintenance Processes: Yes.
Good Technical Design: Proven with extensive deployment and
experience.
Extensible: Yes.
No Hard Scalability bound: Yes.
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Threats Sufficiently Mitigated: Yes.
13.1.2. Babel Success Factos
Babel exhibits the following critical initial success factors:
Positive Net Value:
Hardware cost: None.
Operational interface: ??.
Retraining: None.
Business dependencies: None.
Incremental Deployment: Yes.
Open Code Availability: Yes. One implementation.
Freedom from Usage Restrictions: Yes.
Open Specification Availability: Yes.
Open Maintenance Processes: No.
Good Technical Design: Yes, but less widely deployed/proven than
IS-IS.
Extensible: Yes.
No Hard Scalability bound: No.
Threats Sufficiently Mitigated: ??.
13.2. Willing Implementors
Are there implementers who are ready to implement the technology in
ways that are likely to be deployed?
13.2.1. IS-IS
There is only one implementation of source-specific routing for IS-
IS. [Has it ever been extended by people who are not the authors?
If so, who? -- jch]
[I suggest the rest of this section should be removed. -- jch]
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As all major routing vendors have IS-IS implementations as well as
the existence of for sale and open source implementations, the
barrier for implmeneting IS-IS for homenet use is quite low. Given
this we can assume that willingness to implement modifications (if
any) for homenet use is present and strong.
13.2.2. Babel
The Babel implementation is open source software (MIT licensed, non-
copyleft), and the codebase has proven of sufficiently high quality
to be easily extended by people who were not in direct contact with
the author [RFC7298].
13.3. Willing Customers
Are there customers (especially high-profile customers) who are ready
to deploy the technology?
13.3.1. IS-IS
Yes. IS-IS is already widely deployed in operational networks.
[I suggest more details should be given. Recall that we're speaking
of source-specific IS-IS here. -- jch]
13.3.2. Babel
Babel is currently deployed as part of the OpenWRT and CeroWRT
operating systems. Additionally, the current version is used as a
testbed for the Homenet configuration protocol.
13.4. Potential Niches
Are there potential niches where the technology is compelling?
13.4.1. IS-IS
13.4.2. Babel
Babel is a simple and flexible routing protocol. Like most distance-
vector protocols, it requires little to no configuration in most
topologies, and has proved popular in scenarios where competent
network administration was not available. In addition, it has been
shown to be particularly useful in scenarios where non-standard
metrics were needed, notably wireless mesh networks and overlay
networks.
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13.5. Complexity Removal
If so, can complexity be removed to reduce cost?
13.5.1. IS-IS
As mentioned previously IS-IS can be significantly and easily paired
down to fit the more limited scope of homenet use.
[Any actual implementations the reader can examine? -- jch]
13.5.2. Babel
Babel is a fairly simple protocol -- RFC 6126 is just 40 pages long
(not counting informative appendices), and it has been successfully
explained to fourth year university students in less than two hours.
The stub-only implementation of Babel consists of 900 lines of C
code, and has deliberately been kept as simple as possible. We
expect a competent engineer to get up to speed with it within hours.
13.6. Killer App
Is there a potential killer app? Or can the technology work
underneath existing unmodified applications?
13.6.1. IS-IS
As IS-IS already qualifies as successful (bordering on wildly) a
killer app is not particularly relevant.
13.6.2. Babel
Since Babel requires virtually no configuration, it is particularly
suitable to scenarios where a dedicated network administrator is not
available. Additionally, its support for link quality sensing and
non-standard metrics makes it particularly appealing in highly
heterogeneous networks, (networks built on multiple link-layer
technologies with widely varying performance characteristics).
13.7. Extensible
Is the protocol sufficiently extensible to allow potential
deficiencies to be addressed in the future?
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13.7.1. IS-IS
IS-IS has been shown to be incredibly extensible, originally designed
for a completely different protocol stack (OSI) it was easily adapted
for IP use, then to multiple address families (IPv4, IPv6) and multi-
topology. Indeed one of the major drivers of IS-IS's success is its
extensibility and adaptability.
13.7.2. Babel
The extension mechanisms built into the Babel protocol [BABEL-EXT]
have been shown to be a solid basis on which many backwards-
compatible extensions have been built, including one that
fundamentally changes the structure of announcements [BABEL-SS] and
one that needed a non-trivial extension to the space of metrics
[BABEL-Z].
13.8. Success Predictable
If it is not known whether the protocol will be successful, should
the market decide first? Or should the IETF work on multiple
alternatives and let the market decide among them? Are there factors
listed in this document that may predict which is more likely to
succeed?
13.8.1. IS-IS
For IS-IS the market has already decided that the protocol is
successful in a fairly wide variety of deployments.
13.8.2. Babel
Source-specific Babel is probably the only source-specific routing
protocol that has seen a fair amount of deployment and is being used
in production.
Plain Babel has seen a modest amount of deployment, most notably for
routing over wireless mesh networks and large-scale overlay networks.
However, it remains a young protocol, certainly much younger than IS-
IS.
14. Informative References
[BABEL-EXT]
Chroboczek, J., "Extension Mechanism for the Babel Routing
Protocol", Internet Draft draft-chroboczek-babel-
extension-mechanism-03, June 2013.
Wasserman, et al. Expires August 13, 2015 [Page 14]
Internet-Draft HOMENET IS-IS and Babel Comparison February 2015
[BABEL-SS]
Boutier, M. and J. Chroboczek, "Source-Specific Routing in
Babel", Internet Draft draft-boutier-babel-source-
specific-00, November 2014.
[BABEL-Z] Chroboczek, J., "Diversity Routing for the Babel Routing
Protocol", Internet Draft draft-chroboczek-babel-
diversity-routing-00, July 2014.
[RFC1142] Oran, D., "OSI IS-IS Intra-domain Routing Protocol", RFC
1142, February 1990.
[RFC6126] Chroboczek, J., "The Babel Routing Protocol", RFC 6126,
April 2011.
[RFC7298] Ovsienko, D., "Babel Hashed Message Authentication Code
(HMAC) Cryptographic Authentication", RFC 7298, July 2014.
[SS-ROUTING]
Boutier, M. and J. Chroboczek, "Source-sensitive routing",
December 2014, <http://arxiv.org/abs/1403.0445>.
Authors' Addresses
Margaret Wasserman
Painless Security
356 Abbott Street
North Andover, MA 01845
USA
Phone: +1 781 405-7464
Email: mrw@painless-security.com
URI: http://www.painless-security.com
Christian E. Hopps
Deutsche Telekom
Email: chopps@rawdofmt.org
Juliusz Chroboczek
University of Paris-Diderot (Paris 7)
Email: jch@pps.univ-paris-diderot.fr
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