One document matched: draft-ietf-lisp-map-versioning-04.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd" [
<!ENTITY rfc2119 PUBLIC ''
'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml'>
<!ENTITY LISP PUBLIC ''
'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-lisp.xml'>
<!ENTITY ALT PUBLIC ''
'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-lisp-alt.xml'>
<!ENTITY MS PUBLIC ''
'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-lisp-ms.xml'>
<!ENTITY INTERWORKING PUBLIC ''
'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-lisp-interworking.xml'>
<!ENTITY SECURITY PUBLIC ''
'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-lisp-threats-00.xml'>
<!ENTITY OPENLISP PUBLIC ''
'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-iannone-openlisp-implementation-01.xml'>
]>
<rfc category="exp" ipr="trust200902" docName="draft-ietf-lisp-map-versioning-04.txt">
<?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?>
<?rfc toc="yes" ?>
<?rfc symrefs="yes" ?>
<?rfc sortrefs="yes"?>
<?rfc iprnotified="no" ?>
<?rfc strict="yes" ?>
<?rfc compact="yes" ?>
<?rfc subcompact="no" ?>
<front>
<title>LISP Map-Versioning</title>
<author fullname="Luigi Iannone" initials="L." surname="Iannone">
<organization> TU Berlin - Deutsche Telekom Laboratories AG</organization>
<address>
<postal>
<street>Ernst-Reuter Platz 7</street>
<city>Berlin</city>
<country>Germany</country>
</postal>
<email> luigi@net.t-labs.tu-berlin.de </email>
</address>
</author>
<author fullname="Damien Saucez" initials="D." surname="Saucez" >
<organization> Universite catholique de Louvain
</organization>
<address>
<postal>
<street>Place St. Barbe 2</street>
<city>Louvain-la-Neuve</city>
<country>Belgium</country>
</postal>
<email>damien.saucez@uclouvain.be</email>
</address>
</author>
<author fullname="Olivier Bonaventure" initials="O." surname="Bonaventure">
<organization> Universite catholique de Louvain
</organization>
<address>
<postal>
<street>Place St. Barbe 2</street>
<city>Louvain-la-Neuve</city>
<country>Belgium</country>
</postal>
<email>olivier.bonaventure@uclouvain.be</email>
</address>
</author>
<date year="2011"/>
<abstract>
<t> This document describes the LISP (Locator/ID Separation
Protocol) Map-Versioning mechanism, which provides in-packet
information about Endpoint-ID to Routing Locator (EID-to-RLOC)
mappings used to encapsulate LISP data packets.
The proposed approach is based on associating a version number to
EID-to-RLOC mappings and transport such a version number in the
LISP specific header of LISP-encapsulated packets.
LISP Map-Versioning is particularly useful to inform communicating
Ingress Tunnel Routers (ITRs) and Egress Tunnel Routers (ETRs)
about modifications of the mappings used to encapsulate
packets. The mechanism is transparent to legacy implementations,
since in the LISP-specific header and in the Map Records, bits
used for Map-Versioning can be safely ignored by ITRs and ETRs
that do not support the mechanism.
</t>
</abstract>
</front>
<middle>
<section title="Introduction" anchor="intro">
<t>
This document describes the Map-Versioning mechanism
used to provide information on changes in the EID-to-RLOC
mappings used in the LISP (<xref target="I-D.ietf-lisp"/>)
context to perform packet encapsulation.
The mechanism is totally transparent to xTRs not
supporting such functionality. It is not meant to replace any
existing LISP mechanism, but rather to extend them providing
new functionalities.
The basic mechanism is to associate a Map-Version number to each
LISP EID-to-RLOC mapping and transport such a version number in
the LISP-specific header.
When a mapping changes, a new version number is assigned to
the updated mapping.
A change in an EID-to-RLOC mapping can be a change in the RLOCs
set, by adding or removing one or more RLOCs, but it can also be
a change in the priority or weight of one or more RLOCs.
</t>
<t>
When Map-Versioning is used, LISP-encapsulated data packets
contain the version number of the two mappings used to select
the RLOCs in the outer header (i.e., both source and destination).
These version numbers are encoded in the 24 low-order bits of
the first longword of the LISP header and indicated by a
specific bit in the flags (first 8 high-order bits of the first
longword of the LISP header).
Note that not all packets need to carry version numbers.
</t>
<t>
When an ITR encapsulates a data packet, with a LISP header
containing the Map-Version numbers, it puts in the LISP-specific
header two version numbers:
</t>
<t>
<list style="numbers">
<t>
The version number assigned to the mapping (contained in
the EID-to-RLOC Database) used to select the source RLOC.
</t>
<t>
The version number assigned to the mapping (contained in
the EID-to-RLOC Cache) used to select the destination RLOC.
</t>
</list>
</t>
<t>
This operation is two-fold. On the one hand, it enables the ETR
receiving the packet to know if the ITR has the latest version
number that any ETR at the destination EID site has provided to
the ITR in a Map-Reply.
If it is not the case the ETR can send to the ITR a Map-Request
containing the updated mapping or soliciting a Map-Request from
the ITR (both cases are already defined in
<xref target="I-D.ietf-lisp"/>).
In this way the ITR can update its cache.
On the other hand, it enables an ETR receiving such a packet to
know if it has in its EID-to-RLOC Cache the latest mapping for
the source EID (in case of bidirectional traffic).
If it is not the case a Map-Request can be sent.
</t>
</section> <!-- Introduction -->
<section title="Requirements Notation">
<t>
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 <xref target="RFC2119"/>.
</t>
</section> <!-- Requirements Notation -->
<section title="Definitions of Terms">
<t>
The present document uses terms already defined in
main LISP specification <xref target="I-D.ietf-lisp"/>.
Hereafter are defined only the terms that are specific to the
Map-Versioning mechanism.
</t>
<t>
<list hangIndent="2" style="hanging">
<t hangText="Map-Version number:"> An unsigned 12-bits
assigned to an EID-to-RLOC mapping, not including the value 0
(0x000).
</t>
<t hangText="Null Map-Version:"> The 12-bits null value of 0
(0x000) is not used as Map-Version number. It is used to
signal that no Map-Version number is assigned to the
EID-to-RLOC mapping.
</t>
<t hangText="Source Map-Version number:"> Map-Version number
of the EID-to-RLOC mapping used to select the source address
(RLOC) of the outer IP header of LISP-encapsulated packets.
</t>
<t hangText="Destination Map-Version number:"> Map-Version
number of the EID-to-RLOC mapping used to select the
destination address (RLOC) of the outer IP header of
LISP-encapsulated packets.
</t>
</list>
</t>
</section> <!-- Definitions of Terms -->
<section title="EID-to-RLOC Map-Version number" anchor="vnum">
<t>
The EID-to-RLOC Map-Version number consists in an unsigned
12-bits integer.
The version number is assigned on a per-mapping basis,
meaning that different mappings have a different version
number, which is also updated independently. An update in the
version number (i.e., a newer version) consists in incrementing
by one the older version number. <xref target="a_wraparound"/>
contains a rough estimation of the wrap-around time for the
Map-Version number.
</t>
<t>
The space of version numbers has a circular order where half of
the version numbers is greater than the current Map-Version
number and the other half is smaller than current Map-Version
number.
In a more formal way, assuming we have two version numbers V1
and V2 and that the numbers are expressed on N bits,
the following three cases may happen:
</t>
<t>
<list hangIndent="2" style="hanging">
<t hangText="V1 = V2 :"> This is the exact match case.
</t>
<t hangText="V1 < V2 :">
True if and only if V1 < V2 < (V1 + 2**(N-1)).
</t>
<t hangText="V1 > V2 :">
True if and only if V1 > V2 > (V1 - 2**(N-1)).
</t>
</list>
</t>
<t> Using 12 bits, as defined in this document, and assuming a
Map-Version value of 69, Map-Version numbers in the range
[70; 69 + 2047] are greater than 69, while Map-Version numbers in
the range [69 + 2048; (69 + 4095) mod 4096] are smaller than 69.
</t>
<t>
The initial Map-Version number of a new EID-to-RLOC mapping SHOULD
be randomly generated. However, it MUST NOT be set to the Null
Map-Version value (0x000), because it has a special meaning (see
<xref target="sec_null"/>).
</t>
<section title="The Null Map-Version" anchor="sec_null">
<t>
The value 0x000 (zero) is not a valid Map-Version number
indicating the version of the EID-to-RLOC mapping.
Such a value is used for special purposes and is named the
Null Map-Version number.
</t>
<t>
The Null Map-Version MAY appear in the LISP specific header as
either Source Map-Version number (cf. <xref target="smvn"/>)
or Destination Map-Version number
(cf. <xref target="dmvn"/>).
When the Source Map-Version number is set to the Null
Map-version value it means that no map version information is
conveyed for the source site. This means that if a mapping
exists for the source EID in the EID-to-RLOC Cache, then the
ETR MUST NOT compare the received Null Map-Version with the
content of the EID-to-RLOC cache.
When the Destination Map-version number is set to the Null
Map-version value it means that no map version information is
conveyed for the destination site. This means that the ETR
MUST NOT compare the value with the Map-Version number of the
mapping for the destination EID present in the EID-to-RLOC
Database.
</t>
<t>
The other use of the Null Map-Version number is in the
Map Records, which are part of the Map-Request, Map-Reply
and Map-Register messages (defined in
<xref target="I-D.ietf-lisp"/>).
Map Records that have a Null Map-Version number indicate that
there is no Map-Version number associated with the
mapping. This means that LISP encapsulated packets, destined
to the EID-Prefix the Map Record refers to, MUST either not
contain any Map-Version numbers (V bit set to 0), or if it
contains Map-Version numbers (V bit set to 1) then the
destination Map-Version number MUST be set to the Null
Map-Version number.
Any value different from zero means that Map-Versioning is
supported and MAY be used.
</t>
<t>
The fact that the 0 value has a special meaning for the
Map-Version number implies that, when updating a Map-Version
number because of a change in the mapping, if the next value
is 0 then Map-Version number MUST be incremented by 2 (i.e.,
set to 1, which is the next valid value).
</t>
</section> <!-- Null Map-Version -->
</section> <!-- version number -->
<section title="Dealing with Map-Version numbers" anchor="dealing">
<t>
The main idea of using Map-Version numbers is that whenever
there is a change in the mapping (e.g., adding/removing
RLOCs, a change in the weights due to TE policies, or
a change in the priorities) or a LISP site realizes that one
or more of its own RLOCs are not reachable anymore from a local
perspective (e.g., through IGP, or policy changes) the LISP
site updates the mapping also assigning a new Map-Version
number.
</t>
<t>
To each mapping, a version number is associated and
changes each time the mapping is changed. Note that
map-versioning does not introduce new problems concerning the
coordination of different ETRs of a domain.
Indeed, ETRs belonging to the same LISP site must return for a
specific EID-prefix the same mapping, including the same
Map-Version number.
In principle this is orthogonal to whether or not map-versioning
is used. The synchronization problem is out of the scope
of this document.
</t>
<t>
In order to announce in a data-driven fashion that the mapping
has been updated, Map-Version numbers used to create the
outer IP header of the LISP-encapsulated packet are embedded in
the LISP-specific header.
This means that the header needs to contain two Map-Version
numbers:
</t>
<t>
<list style="symbols">
<t>
The Source Map-Version number of the EID-to-RLOC mapping
in the EID-to-RLOC Database used to select the source RLOC.
</t>
<t>
The Destination Map-Version number of the EID-to-RLOC
mapping in the EID-to-RLOC Cache used to select the
destination RLOC.
</t>
</list>
</t>
<t>
By embedding both Source Map-Version number and Destination
Map-Version number an ETR receiving a LISP packet with
Map-Version numbers, can perform the following checks:
<list style="numbers">
<t>
The ITR that has sent the packet has an up-to-date
mapping in its cache for the destination EID and is
performing encapsulation correctly.
</t>
<t>
In case of bidirectional traffic, the mapping in the local
ETR EID-to-RLOC cache for the source EID is up-to-date.
</t>
</list>
If one or both of the above conditions do not hold, the ETR can
send a Map-Request either to make the ITR aware that a new
mapping is available (see <xref target="dmvn"/>) or to
update the mapping in the local cache (see <xref
target="smvn"/>).
</t>
<section title="Handling Destination Map-Version number"
anchor="dmvn">
<t>
When an ETR receives a packet, the Destination Map-Version
number relates to the mapping for the destination EID for
which the ETR is a RLOC. This mapping is part of the ETR
EID-to-RLOC Database. Since the ETR is authoritative for the
mapping, it has the correct and up-to-date Destination
Map-Version number.
A check on this version number can be done, where the following
cases can arise:
<list style="numbers">
<t>
The packets arrive with the same Destination Map-Version
number stored in the EID-to-RLOC Database. This is the
regular case.
The ITR sending the packet has in its EID-to-RLOC Cache an
up-to-date mapping. No further actions are needed.
</t>
<t>
The packet arrives with a Destination Map-Version
number greater (i.e., newer) than the one stored in the
EID-to-RLOC Database.
Since the ETR is authoritative on the mapping, meaning
that the Map-Version number of its mapping is the correct
one, this implies that someone is not behaving correctly
with respect to the specifications. In this case the packet
carries a version number that is not valid, otherwise the
ETR would have the same, and SHOULD be silently
dropped.
</t>
<t>
The packets arrive with a Destination Map-Version
number smaller (i.e., older) than the one stored in the
EID-to-RLOC Database.
This means that the ITR sending the packet has an old
mapping in its EID-to-RLOC Cache containing stale
information.
The ITR sending the packet has to be informed that a newer
mapping is available.
This is done with a Map-Request message sent back to the
ITR. The Map-Request will either trigger a Map-Request
back using the Solicit-Map-Request (SMR) bit or it will
piggyback the newer mapping.
These are not new mechanisms; how to SMR or piggyback
mappings in Map-Request messages is already described in
<xref target="I-D.ietf-lisp"/>, while their security is
discussed in
<xref target="I-D.ietf-lisp-threats"/>.
These Map-Request messages should be rate limited (rate
limitation policies are also described in
<xref target="I-D.ietf-lisp"/>).
The feature introduced by Map-Version numbers is the
possibility of blocking traffic not using the latest
mapping. Indeed, after a certain number of retries,
if the Destination Map-Version number in the packets is
not updated, the ETR MAY drop packets with a
stale Map-Version number while strongly reducing the rate
of Map-Request messages. This because either the ITR is
refusing to use the mapping for which the ETR is
authoritative or (worse) it might be some form of attack.
Another case might be that the control-plane is
experiencing transient failures so the Map-Requests cannot
reach that ITR. By keeping sending Map-Requests at very
low rate it is possible to recover from this situation.
</t>
</list>
The rule in the third case MAY be more restrictive. If
the mapping has been the same for a period of time as long as
the TTL (defined in <xref target="I-D.ietf-lisp"/>) of
the previous version of the mapping, all packets arriving with
an old Map-Version SHOULD be silently dropped right away
without issuing any Map-Request.
The reason that allows such action is the fact that if the new
mapping with the updated version number has been unchanged for
at least the same time as the TTL of the older mapping, all the
entries in the caches of ITRs must have expired. Hence, all
ITRs sending traffic should have refreshed the mapping
according to <xref target="I-D.ietf-lisp"/>.
If packets with old Map-Version number are still received,
then either someone has not respected the TTL, or it is a form
of spoof/attack. In both cases this is not valid behavior
with respect to the specifications and the packet SHOULD be
silently dropped.
</t>
<t>
LISP-encapsulated packets with the V-bit set, when the
original mapping in the EID-to-RLOC Database has version
number set to the Null Map-Version value, MAY be silently
dropped.
As explained in <xref target="sec_null"/>, if an EID-to-RLOC
mapping has a Null Map-Version, it means that ITRs, using the
mapping for encapsulation, MUST NOT use Map-Version number
in the LISP-specific header.
</t>
<t>
For LISP-encapsulated packets with the V-bit set, when the
original mapping in the EID-to-RLOC Database has version number
set to a value different from the Null Map-Version value,
a Destination Map-Version number equal to the Null Map-Version
value means that the Destination Map-Version number MUST be
ignored.
</t>
</section> <!-- Handling Destiantion Map-Version number -->
<section title="Handling Source Map-Version number"
anchor="smvn">
<t>
When an ETR receives a packet, the Source Map-Version
number relates to the mapping for the source EID for which
the ITR that sent the packet is authoritative.
If the ETR has an entry in its EID-to-RLOC Cache for the
source EID, then a check can be performed and the following
cases can arise:
<list style="numbers">
<t>
The packet arrives with the same Source Map-Version
number stored in the EID-to-RLOC Cache. This is the correct
regular case. The ITR has in its cache an up-to-date copy
of the mapping. No further actions are needed.
</t>
<t>
The packet arrives with a Source Map-Version number
greater (i.e., newer) than the one stored in the local
EID-to-RLOC Cache. This means that ETR has in its cache a
mapping that is stale and needs to be updated.
A Map-Request SHOULD be sent to get the new mapping for
the source EID.
This is a normal Map-Request message sent through the
mapping system and MUST respect the specifications in
<xref target="I-D.ietf-lisp"/>, including rate limitation
policies.
</t>
<t>
The packet arrives with a Source Map-Version number
smaller (i.e., older) than the one stored in the local
EID-to-RLOC Cache. Such a case is not valid with respect
to the specifications.
Indeed, if the mapping is already present in the
EID-to-RLOC Cache, this means that an explicit Map-Request
has been sent and a Map-Reply has been received from an
authoritative source. Assuming that the mapping system is
not corrupted anyhow, the Map-Version in the EID-to-RLOC
Cache is the correct one, while the one carried by the
packet is stale. In this situation the packet MAY be
silently dropped.
</t>
</list>
</t>
<t>
If the ETR does not have an entry in the EID-to-RLOC Cache for
the source EID (e.g., in case of unidirectional traffic) then
the Source Map-Version number can be safely ignored.
</t>
<t>
For LISP-encapsulated packets with the V-bit set, if the
Source Map-Version number is the Null Map-Version value, it
means that the Source Map-Version number MUST be ignored.
</t>
</section> <!-- Handling Source Map-Version Number -->
</section> <!-- Dealing Mapping Version numbers -->
<section title="LISP header and Map-Version numbers" anchor="lisphdr">
<t>
In order for the versioning approach to work, the LISP
specific header has to carry both Source Map-Version number
and Destination Map-Version number.
This is done by setting the V-bit in the LISP specific header as
defined in <xref target="I-D.ietf-lisp" /> Section 5.3.
When the V-bit is set the low-order 24-bits of the first
longword are used to transport both source and destination
Map-Version numbers.
In particular the first 12 bits are used for Source Map-Version
number and the second 12 bits for the Destination Map-Version
number.
</t>
<t>
Hereafter is the example of LISP header carrying version
numbers in the case of IPv4-in-IPv4 encapsulation. The same
setting can be used for any other case (IPv4-in-IPv6,
IPv6-in-IPv4, and IPv6-in-IPv6).
</t>
<figure>
<artwork>
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ |N|L|E|V|I|flags| Source Map-Version |Destination Map-Version|
LISP+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | Instance ID/Locator Status Bits |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>
<list hangIndent="2" style="hanging">
<t hangText="Source Map-Version number (12 bits):">
Map-Version of the mapping used by the ITR to select the RLOC
present in the "Source Routing Locator" field. How to set on
transmission and handle on reception this value is
described in <xref target="smvn"/>.
</t>
<t hangText="Destination Map-Version number (12 bits):">
Map-Version of the mapping used by the ITR to select the RLOC
present in the "Destination Routing Locator" field.
How to set on transmission and handle on reception this
value is described in <xref target="dmvn"/>.
</t>
</list>
</t>
<t>
The present document just specifies how to use the
low-order 24-bits of the first longword of the LISP-specific
header when the V-bit is set to 1. All other cases,
including the bit fields of the rest of the LISP-specific header
and the whole LISP packet format are specified in
<xref target="I-D.ietf-lisp"/>.
Not all of the LISP encapsulated packets need to carry version
numbers.
When Map-Version numbers are carried the V-bit MUST be
set to 1. All legal combinations of the flags, when the V-bit
is set to 1, are described in <xref target="I-D.ietf-lisp"/>.
</t>
</section> <!-- LISP Header -->
<section title="Map Record and Map-Version"
anchor= "vnumpkt">
<t>
To accommodate the proposed mechanism, the Map Records that are
transported on Map-Request/Map-Reply/Map-Register messages need
to carry the Map-Version number as well.
For this purpose the 12-bits before the EID-AFI field in the
Record that describe a mapping is used. This is defined in
Section 6.1.4 of <xref target="I-D.ietf-lisp"/> and reported
here as example.
</t>
<t>
<figure>
<artwork>
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
+-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Record TTL |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
R | Locator Count | EID mask-len | ACT |A| Reserved |
e +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
c | Rsvd | Map-Version Number | EID-prefix-AFI |
o +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
r | EID-prefix |
d +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| /| Priority | Weight | M Priority | M Weight |
| L +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| o | Unused Flags |L|p|R| Loc-AFI |
| c +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| \| Locator |
+-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<list hangIndent="2" style="hanging">
<t hangText="Map-Version Number:">
Map-Version of the mapping contained in the Record.
As explained in <xref target="sec_null"/> this field can be
zero (0), meaning that no Map-Version is associated to the
mapping, hence packets that are LISP-encapsulated using this
mapping MUST NOT contain Map-Version numbers in the LISP
specific header and the V-bit MUST be set to 0.
</t>
</list>
</t>
<t>
This packet format works perfectly with xTRs that do not support
Map-Versioning, since they can simply ignore those bits.
</t>
</section> <!-- Map Record and Map-Version -->
<section title="Benefits and case studies for Map-Versioning">
<t>In the following sections we provide more discussion on various
aspects and use of the Map-Versioning. Security observations are
instead grouped in <xref target="security"/>.
</t>
<section title="Synchronization of different xTRs" anchor="synch">
<t>
Map-Versioning does not require additional synchronization
mechanism compared to the normal functioning of LISP without
Map-Versioning. Clearly all the ETRs have to reply with the
same Map-Version number, otherwise there can be an inconsistency
that creates additional control traffic, instabilities, traffic
disruptions. It is the same without Map-Versioning, with ETRs
that have to reply with the same mapping, otherwise the same
problems can arise.
</t>
<t>
As an example, let's consider the topology of
<xref target="vtraffic"/> where ITR A.1 of domain A is sending
unidirectional traffic to the domain B, while A.2 of
domain A exchange bidirectional traffic with domain B. In
particular, ITR A.2 send traffic to ETR B and ETR A.2 receives
traffic from ITR B.
</t>
<t>
<figure anchor="vtraffic">
<artwork><![CDATA[
+-----------------+ +-----------------+
| Domain A | | Domain B |
| +---------+ | |
| | ITR A.1 |--- | |
| +---------+ \ +---------+ |
| | ------->| ETR B | |
| | ------->| | |
| +---------+ / | | |
| | ITR A.2 |--- -----| ITR B | |
| | | / +---------+ |
| | ETR A.2 |<----- | |
| +---------+ | |
| | | |
+-----------------+ +-----------------+
]]></artwork>
</figure>
</t>
<t>
Obviously in the case of Map-Versioning both ITR A.1 and ITR A.2
of domain A must use the same value otherwise the ETR of domain
B will start to send Map-Requests.
</t>
<t>
The same problem can, however, arise without Map-Versioning.
For instance, if the two ITRs of domain A send different Loc
Status Bits. In this case either the traffic is disrupted, if
the ETR B trusts the Locator Status Bits, or if ETR B does not
trusts the Locator Status Bits it will start sending
Map-Requests to confirm the each change in the reachability.
</t>
<t>
So far, LISP does not provide any specific synchronization
mechanism, but assumes that synchronization is provided by
configuring the different xTRs consistently.
The same applies for Map-Versioning. If in the future any
synchronization mechanism is provided, Map-Versioning will
take advantage of it automatically since it is included in
the Record format, as described in <xref target="vnumpkt"/>.
</t>
</section> <!-- Synchronization -->
<section title="Map-Versioning and unidirectional traffic" anchor="utrf">
<t>
When using Map-Versioning the LISP specific header carries two
Map-Version numbers, for both source and destination mappings.
This can raise the question on what will happen in the case of
unidirectional flows, like for instance in the case presented in
<xref target="utraffic"/>, since LISP specification do
not mandate for ETR to have a mapping for the source EID.
<figure anchor="utraffic">
<artwork><![CDATA[
+-----------------+ +-----------------+
| Domain A | | Domain B |
| +---------+ +---------+ |
| | ITR A |----------->| ETR B | |
| +---------+ +---------+ |
| | | |
+-----------------+ +-----------------+
]]></artwork>
</figure>
</t>
<t>
For what concerns the ITR, it is able to put both source and
destination version number in the LISP header since the Source
Map-Version number is in ITR's database, while the
Destination Map-Version number is in ITR's cache.
</t>
<t>
For what concerns the ETR, it simply checks only the Destination
Map-Version number in the same way as described in
<xref target="dealing"/>, ignoring the Source Map-Version
number.
</t>
</section> <!-- Unidirectional Traffic -->
<section title="Map-Versioning and interworking">
<t>
Map-Versioning is compatible with the LISP interworking
between LISP and non-LISP sites as defined in
<xref target="I-D.ietf-lisp-interworking"/>.
LISP interworking defines three techniques to make LISP sites
and non-LISP sites, namely Proxy-ITR, LISP-NAT, and Proxy-ETR.
Hereafter it is described how Map-Versioning relates to these
three mechanisms.
</t>
<section title="Map-Versioning and Proxy-ITRs" anchor="pitr">
<t>
The purpose of the Proxy-ITR (PITR) is to encapsulate traffic
originating in a non-LISP site in order to deliver the packet
to one of the ETRs of the LISP site (cf.
<xref target="fpitr"/>).
This case is very similar to the unidirectional traffic case
described in <xref target="utrf"/>, hence similar rules apply.
<figure anchor="fpitr">
<artwork><![CDATA[
+----------+ +-------------+
| LISP | | non-LISP |
| Domain A | | Domain B |
| +-------+ +-----------+ | |
| | ETR A |<-------| Proxy ITR |<-------| |
| +-------+ +-----------+ | |
| | | |
+----------+ +-------------+
]]></artwork>
</figure>
</t>
<t>
The main difference is that a Proxy-ITR does not have any
mapping, since it just encapsulate packets arriving
from non-LISP site, thus cannot provide a Source Map-Version.
In this case, the proxy-ITR will just put the Null Map-Version
value as Source Map-Version number, while the receiving ETR
will ignore the field.
</t>
<t>
With this setup the LISP Domain A is able to check whether or
not the PITR is using the latest mapping. If this is not the
case the mapping for LISP Domain A on the PITR can be updated
using one of the mechanisms defined in
<xref target="I-D.ietf-lisp"/> and
<xref target="I-D.ietf-lisp-interworking"/>.
</t>
</section> <!-- Proxy-ITRs -->
<section title="Map-Versioning and LISP-NAT" anchor="lispnat">
<t>
The LISP-NAT mechanism is based on address translation from
non-routable EIDs to routable EIDs and does not involve any
form of encapsulation. As such Map-Versioning does not apply
in this case.
</t>
</section> <!-- LISP-NAT -->
<section title="Map-Versioning and Proxy-ETRs" anchor="petr">
<t>
The purpose of the Proxy-ETR (PETR) is to decapsulate traffic
originating in a LISP site in order to deliver the packet
to the non-LISP site (cf. <xref target="fpetr"/>).
One of the main reasons of deploy PETRs is to bypass uRPF
(Unicast Reverse Path Forwarding) checks on the provider edge.
<figure anchor="fpetr">
<artwork><![CDATA[
+----------+ +-------------+
| LISP | | non-LISP |
| Domain A | | Domain B |
| +-------+ +-----------+ | |
| | ITR A |------->| Proxy ETR |------->| |
| +-------+ +-----------+ | |
| | | |
+----------+ +-------------+
]]></artwork>
</figure>
</t>
<t>
A Proxy-ETR does not have any mapping, since it just
decapsulates packets arriving from LISP site.
In this case, the ITR will just put the Null Map-Version
value as Destination Map-Version number, while the receiving
Proxy-ETR will ignore the field.
</t>
<t>
With this setup the Proxy-ETR is able to check whether or not
the mapping has changed. If this is the case the mapping for
LISP Domain A on the PETR can be updated using one of the
mechanisms defined in <xref target="I-D.ietf-lisp"/> and
<xref target="I-D.ietf-lisp-interworking"/>.
</t>
</section> <!-- Proxy-ETRs -->
</section> <!-- Map-Versionin and LISP interworking -->
<section title="RLOC shutdown/withdraw" anchor="shutdown">
<t>
Map-Versioning can be even used to perform a graceful shutdown
or withdraw of a specific RLOC.
This is achieved by simply issuing a new mapping, with an
updated Map-Version number, where the specific RLOC to be shut
down is withdrawn or announced as unreachable (R bit in the Map
Record, see <xref target="I-D.ietf-lisp"/>), but without
actually turning it off.
</t>
<t>
Once no more traffic is received by the RLOC, it can be shut
down gracefully, because at least all sites actively using the
mapping have updated it.
</t>
<t>
It should be pointed out that for frequent up/down changes such
a mechanism should not be used since this can generate excessive
load on the Mapping System.
</t>
</section> <!-- RLOC Shutdown/Withdraw -->
<section title="Map-Version for lightweight LISP implementation"
anchor="light">
<t>
The use of Map-Versioning can help in developing a lightweight
implementation of LISP. This comes with the price of not
supporting Loc-Status-Bit, which are useful in some contexts.
</t>
<t>
In the current LISP specifications the set of RLOCs must always
be maintained ordered and consistent with the content of the Loc
Status Bits (see section 6.5 of <xref target="I-D.ietf-lisp"/>).
With Map-Versioning such type of mechanisms can be avoided.
When a new RLOC is added to a mapping, it is not necessary to
"append" new locators to the existing ones as explained in
Section 6.5 of <xref target="I-D.ietf-lisp"/>.
A new mapping with a new Map-Version number will be issued, and
since the old locators are still valid the transition will be
with no disruptions.
The same applies for the case a RLOC is withdrawn.
There is no need to maintain holes in the list of
locators, as is the case when using Locator Status Bits, for
sites that are not using the RLOC that has been withdrawn the
transition will be with no disruptions.
</t>
<t>
All of these operations, as already stated, do not need to
maintain any consistency among Locator Status Bits, and the way
RLOC are stored in the cache.
</t>
<t>
Further, Map-Version can be used to substitute the "clock sweep"
operation described in Section 6.5.1 of
<xref target="I-D.ietf-lisp"/>. Indeed, every LISP site
communicating to a specific LISP site that has updated the
mapping will be informed of the available new mapping in a
data-driven manner.
</t>
<t>
Note that what is proposed in the present section is just an
example and MUST NOT be considered as specifications for a
lightweight LISP implementation. In case the IETF decides to
undertake such a work, it will be documented elsewhere.
</t>
</section> <!-- Lightweight Implementation -->
</section> <!-- Benefits Case Studies -->
<section title="Incremental deployment and implementation status"
anchor="truelisp">
<t>
Map-Versioning can be incrementally deployed without any
negative impact on existing LISP elements (e.g., xTRs,
Map-Servers, Proxy-ITRs, etc).
Any LISP element that does not support Map-Versioning can
safely ignore them.
Further, there is no need of any specific mechanism to discover
if an xTR supports or not Map-Versioning. This information
is already included in the Map Record.
</t>
<t>
Map-Versioning is currently implemented in OpenLISP
<xref target="I-D.iannone-openlisp-implementation"/>.
</t>
<t>Note that the reference document for LISP implementation
and interoperability tests remains <xref target="I-D.ietf-lisp"/>.
</t>
</section> <!-- deployment -->
<section title="Security Considerations"
anchor="security">
<t>
Map-Versioning does not introduce any security issue
concerning both the data-plane and the control-plane.
On the contrary, as described in the following, if
Map-Versioning may be used also to update mappings in case of
change in the reachability information (i.e., instead of the
Locator Status Bits) it is possible to reduce the effects of
some DoS or spoofing attacks that can happen in an untrusted
environment.
</t>
<t>
Robustness of the Map-Versioning mechanism leverages on a
trusted Mapping Distribution System.
A thorough security analysis of LISP is documented in
<xref target="I-D.ietf-lisp-threats" />.
</t>
<section title="Map-Versioning against traffic disruption">
<t>
An attacker can try to disrupt ongoing communications by
creating LISP encapsulated packets with wrong Locator Status
Bits. If the xTR blindly trusts the Locator Status Bits it
will change the encapsulation accordingly, which can result in
traffic disruption.
</t>
<t>
This does not happen in the case of Map-Versioning. As
described in <xref target="dealing"/>, upon a version
number change the xTR first issues a Map-Request. The
assumption is that the mapping distribution system is
sufficiently secure that Map-Request and Map-Reply messages
and their content can be trusted.
Security issues concerning specific mapping distribution
system are out of the scope of this document.
In the case of Map-Versioning the attacker should "guess" a
valid version number that triggers a Map-Request, as described
in <xref target="dealing"/>, otherwise the packet is simply
dropped. Nevertheless, guessing a version number that
generates a Map-Request is easy, hence it is important to
follow the rate limitations policies described in
<xref target="I-D.ietf-lisp"/> in order to avoid DoS attacks.
</t>
<t>
Note that a similar level of security can be obtained with Loc
Status Bits, by simply making mandatory to verify any change
through a Map-Request. However, in this case Locator Status
Bits loose their meaning, because, it does not matter anymore
which specific bits has changed, the xTR will query the
mapping system and trust the content of the received
Map-Reply. Furthermore there is no way to perform filtering as
in the Map-Versioning in order to drop packets that do not
carry a valid Map-Version number.
In the case of Locator Status Bits, any random change can
trigger a Map-Request (unless rate limitation is enabled which
raise another type of attack discussed in
<xref target="dos"/>).
</t>
</section> <!-- Traffic Disruption -->
<section title="Map-Versioning against reachability
information DoS"
anchor="dos">
<t>
Attackers can try to trigger a large amount of Map-Request by
simply forging packets with random Map-Version or
random Locator Status Bits.
In both cases the Map-Requests are rate limited as described
in <xref target="I-D.ietf-lisp"/>.
However, differently from Locator Status Bit where there is no
filtering possible, in the case of Map-Versioning is
possible to filter not valid version numbers before triggering
a Map-Request, thus helping in reducing the effects of DoS
attacks.
In other words the use of Map-Versioning enables a fine
control on when to update a mapping or when to notify that a
mapping has been updated.
</t>
<t> It is clear, that Map-Versioning does not protect against
DoS and DDoS attacks, where an xTR looses processing power
doing checks on the LISP header of packets sent by
attackers. This is independent from Map-Versioning and is the
same for Loc Status Bits.
</t>
</section> <!-- Reachability DoS -->
</section> <!-- Security Considerations -->
<section title="IANA Considerations">
<t> This document has no actions for IANA.
</t>
</section> <!-- IANA Considerations -->
<section title="Acknowledgements">
<t> The authors would like to thank Alia Atlas, Jesper Skriver,
Pierre Francois, Noel Chiappa, Dino Farinacci for their comments
and review.
</t>
<t> This work has been partially supported by the
INFSO-ICT-216372 TRILOGY Project (www.trilogy-project.org).
</t>
</section> <!-- Acknowledgements -->
</middle>
<back>
<references title='Normative References'>
&rfc2119;
&LISP;
</references>
<references title='Informative References'>
&ALT;
&MS;
&INTERWORKING;
&SECURITY;
&OPENLISP;
</references>
<!-- Here come the Appendix -->
<section title="Estimation of time before Map-Version wrap-around"
anchor="a_wraparound">
<t>
The present section proposes an estimation of the wrap-around
time for the proposed 12 bits size for the Map-Version number.
Using a granularity of seconds and assuming as worst-case that a
new version is issued each second, it takes slightly more than 1
hour before the version wraps around. Note that the granularity
of seconds is in line with the rate limitation policy for
Map-Request messages, as proposed in the LISP main
specifications (<xref target="I-D.ietf-lisp"/>).
Alternatively a granularity of minutes can also be used, as
for the TTL of the Map-Reply (<xref target="I-D.ietf-lisp"/>).
In this case the worst scenario is when a new version is issued
every minute, leading to a much longer time before
wrap-around. In particular, when using 12 bits, the wrap-around
time is almost 3 days.
</t>
<t>
For general information, hereafter there is a table with a rough
estimation of the time before wrap-around in the worst-case
scenario, considering different sizes (bits length) of the
Map-Version number and different time granularity.
</t>
<figure anchor="wraparound"
title="Estimation of time before wrap-around">
<artwork>
+---------------+--------------------------------------------+
|Version Number | Time before wrap around |
| Size (bits) +---------------------+----------------------+
| |Granularity: Minutes | Granularity: Seconds |
| | (mapping changes | (mapping changes |
| | every 1 minute) | every 1 second) |
+-------------------------------------+----------------------+
| 32 | 8171 Years | 136 Years |
| 30 | 2042 Years | 34 Years |
| 24 | 31 Years | 194 Days |
| 16 | 45 Days | 18 Hours |
| 15 | 22 Days | 9 Hours |
| 14 | 11 Days | 4 Hours |
| 13 | 5.6 Days | 2.2 Hours |
| 12 | 2.8 Days | 1.1 Hours |
+---------------+---------------------+----------------------+
</artwork>
</figure>
</section> <!-- Map-Version Wrap-around -->
<section title="Document Change Log" anchor="log">
<t>
<list hangIndent="2" style="symbols">
<t>Version 04 Posted September 2011.
<list hangIndent="2" style="symbols">
<t>Added clarifications in
<xref target="intro"/>,
<xref target="vnum"/>,
<xref target="smvn"/>, and
<xref target="dmvn"/> to address Stephen Farrell's
comments.
</t>
<t>Used the term LISP Site instead of ISP in
<xref target="dealing"/> as suggested by Stephen Farrell.
</t>
<t>Deleted "(usually contains the nonce)" from
<xref target="lisphdr"/> because confusing, as suggested
by Stephen Farrell.
</t>
<t> Fixed several typos pointed out by Stephen Farrell.
</t>
</list>
</t>
<t>Version 03 Posted September 2011.
<list hangIndent="2" style="symbols">
<t>Added reference in <xref target="vnumpkt"/> toward the
main lisp documents specifying the section, as requested by
Jari Arkko.
</t>
<t>Fixed all typos and editorial issues pointed out by Jari
Arkko.
</t>
<t> Added clarification in <xref target="shutdown"/> as
requested by Jari Arkko.
</t>
<t> Extentend all acronyms in the abstract as requested by
Jari Arkko.
</t>
<t> Clarified silent drop polocy in <xref target="smvn"/>
as requested by both Richard Barnes and Jari Arkko.
</t>
<t> Fixed typos pointed out by Richard Barnes.
</t>
</list>
</t>
<t>Version 02 Posted July 2011.
<list hangIndent="2" style="symbols">
<t>Added text in <xref target="dealing"/> about ETR
synchronization, as suggested by Alia Atlas.
</t>
<t> Modified text in <xref target="light"/>
concerning lightweight LISP implementation, as suggested by
Alia Atlas.
</t>
<t> Deleted text concerning old versions of
<xref target="I-D.ietf-lisp-ms"/> and
<xref target="I-D.ietf-lisp-alt"/> in
<xref target="vnumpkt"/>,
as pointed out by Alia Atlas.
</t>
<t> Fixed section 4.1 to be less restrictive, as suggested
by Jesper Skriver.
</t>
</list>
</t>
<t>Version 01 Posted March 2011.
<list hangIndent="2" style="symbols">
<t> Changed the wording from "Map-Version number 0" to "Null
Map-Version.
</t>
<t> Clarification of the use of the Null Map-Version value
as Source Map-Version Number and Destination Map-Version
Number.
</t>
<t> Extended the section describing Map-Versioning and LISP
Interworking co-existence.
</t>
<t> Reduce packet format description to avoid double
definitions with the main specs.
</t>
</list>
</t>
<t>Version 00 Posted September 2010.
<list hangIndent="2" style="symbols">
<t>Added Section "Definitions of Terms".
</t>
<t>Editorial polishing of all sections.
</t>
<t>Added clarifications in section "Dealing with
Map-Version numbers" for the case of the special
Map-Version number 0.
</t>
<t>Rename of draft-iannone-mapping-versioning-02.txt.
</t>
</list>
</t>
</list>
</t>
</section> <!-- Document Change Log -->
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-23 02:47:55 |