One document matched: draft-ietf-lisp-map-versioning-00.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.draft-ietf-lisp-08.xml'>
<!ENTITY ALT PUBLIC ''
'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-lisp-alt-04.xml'>
<!ENTITY MS PUBLIC ''
'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-lisp-ms-05.xml'>
<!ENTITY INTERWORKING PUBLIC ''
'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-ietf-lisp-interworking-01.xml'>
<!ENTITY SECURITY PUBLIC ''
'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.draft-saucez-lisp-security-01.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-00.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="2010"/>
<abstract>
<t> This document describes the LISP Map-Versioning mechanism,
which provides in-packet information about 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
xTRs 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 xTRs that do not
support the mechanism.
</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<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 a functionality. It is not meant to replace any
existing LISP mechanism, but rather to complete them providing
new functionalities.
The basic mechanism is to associate Map-Version numbers 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 that sent it is using
the latest mapping for the destination EID. If it is not the
case the ETR can send to the ITR a Map-Request containing the
updated mapping or invoking 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 xTR receiving such a packet to
know if it has in its cache the latest mapping for the source
EID (in case of bidirectional traffic).
If it is not the case a Map-Request can be send.
</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>
<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="Map-Version 0:"> The 12-bits value 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.
</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.
</t>
</list>
</t>
</section> <!-- Definitions of Terms -->
<section title="EID-to-RLOC Map-Version number">
<t>
The EID-to-RLOC Map-Version number consists in an unsigned
12-bits integer.
The version number is assigned in a per-mapping fashion, meaning
that different mappings will have assigned a different version
number, which is also updated independently. An update in the
version number (i.e., a newer version) consist 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 can
be randomly generated. However, it MUST NOT be zero (0x000)
because it has a special meaning (see
<xref target="sec_zero"/>).
</t>
<section title="The special Map-Version 0" anchor="sec_zero">
<t>
The value 0x000 (zero) is not a valid Map-Version number
indicating the version of the EID-to-RLOC mapping. The only
valid use of Map-Version number equal to 0 is in the Map
Records, which are part of the Map-Request and Map-Reply
messages (defined in <xref target="I-D.ietf-lisp"/>).
Map Records that have Map-Version number equal 0 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 never contain
Map-Version number (i.e., V bit MUST always be 0). In other
words, Map-Version number equal to 0 signals to the ITR using
the mapping that the Map-Versioning is not supported, or even
if supported it MUST NOT be used for that specific
EID-Prefix.
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> <!-- Map-Version 0 -->
</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 an ISP 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 ISP
updates the mapping also assigning a new Map-Version number.
</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>
A first one from the EID-to-RLOC mapping in the EID-to-RLOC
Database used to select the source RLOC, and called Source
Map-Version number.
</t>
<t>
A second one from the EID-to-RLOC mapping in the EID-to-RLOC
Cache used to select the destination RLOC, and called
Destination Map-Version number.
</t>
</list>
</t>
<t>
By embedding both Source Map-Version number and Destination
Map-Version number an xTR receiving a LISP packet with
Map-Version number, 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
xTR cache for the source EID is up-to-date.
</t>
</list>
If one or both of the above conditions do not hold, the xTR 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 LISP
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 is 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. Further actions are needed.
Since the ETR is authoritative on the mapping, this means
that someone is not behaving correctly w.r.t. the
specifications, thus the packet carries a not valid
version number 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.
Further actions are needed. The ITR sending the packet
must 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 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.saucez-lisp-security"/>.
These Map-Request messages should be rate limited (rate
limitation policies are also described in
<xref target="I-D.ietf-lisp"/>).
The gain introduced by Map-Version Numbers is that
after a certain number of retries, if the Destination
Map-Version number in the packets is not updated,
packet MAY be silently dropped because either the ITR is
refusing to use the mapping for which the ETR is
authoritative or it might be some form of attack.
</t>
</list>
Note that the rule in case 3 can be even more restrictive.
If the mapping has been the same for a period of time as long
as the TTL (defined in LISP <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.
Indeed, if the new mapping with the updated version number has
been stable for at least the same time as the TTL of the older
mapping, all the entries in the caches of ITRs must have
expired. If packets with old Map-Version number are still
received, the reason is that either someone has not respected
the TTL, or it is a form of spoof/attack. In both cases this
is not valid behavior w.r.t. the specifications and the packet
MAY be silently dropped.
</t>
<t>
For LISP-encapsulated packets with the V-bit set, the
Destination Map-Version can never contain the special value 0.
Indeed, as explained in <xref target="sec_zero"/>, if an
EID-to-RLOC mapping has Map-Version 0, it means that ITRs,
using the mapping for encapsulation, MUST NOT put Map-Version
number in the LISP-specific header. An ETR receiving a packet
with the V-bit set but Destination Map-Version 0 SHOULD
silently drop the packet.
</t>
</section> <!-- Handling Destiantion Map-Version number -->
<section title="Handling Source Map-Version number"
anchor="smvn">
<t>
When an xTR 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 xTR does
not have an entry in the LISP Cache for the source EID, then
the Source Map-Version number can be safely ignored.
If the xTR has an entry in its LISP Cache for the source EID,
then a check is performed and the following cases can arise:
<list style="numbers">
<t>
The packet arrives with the same Source Map-Version
number stored in the LISP Cache. This is the correct
regular case. The xTR 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
LISP Cache. This means that xTR has in its cache a
mapping that is stale and needs to be updated.
The packet is considered valid but further actions are
needed. In particular a Map-Request must 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
LISP Cache. Such a case is not valid w.r.t. the
specifications. Indeed, if the mapping is already present
in the LISP 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 LISP Cache is
the correct one; hence the packet is not valid and SHOULD
be silently dropped.
</t>
</list>
</t>
<t> Otherwise, if the xTR does not have an entry in its cache
(e.g. unidirectional traffic) the Source Map-Version can be
safely ignored.
</t>
<t>
For LISP-encapsulated packets with the V-bit set, if the
Source Map-Version number is the special value 0, it means
that the Source Map-Version number MUST be ignored.
</t>
</section>
</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.
When the V-bit is set the low-order 24-bits of the first
longword (which usually contains the nonce) 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).
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"/>.
In the following example we include all the headers of a LISP
encapsulated packet just for the sake of clarity.
</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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/|Version| IHL |Type of Service| Total Length |
/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Identification |Flags| Fragment Offset |
/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
OH | Time to Live | Protocol = 17 | Header Checksum |
\ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | Source Routing Locator |
\ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\| Destination Routing Locator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Source Port = xxxx | Dest Port = 4341 |
UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | UDP Length | UDP Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ |N|L|E|V|I|flags| Source Map-Version |Destination Map-Version|
LISP+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | Instance ID/Locator Status Bits |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/|Version| IHL |Type of Service| Total Length |
/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Identification |Flags| Fragment Offset |
/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IH | Time to Live | Protocol | Header Checksum |
\ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | Source EID |
\ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\| Destination EID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>
<list hangIndent="2" style="hanging">
<t hangText="V (1 bit):">
this is the Map-Version bit as defined in
<xref target="I-D.ietf-lisp"/>. When this bit is set to 1 the
low-order 24-bits of the first longword of the LISP header
contain Map-Version numbers.
</t>
<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. Note that the
mapping used for such a selection is determined by the
Source EID through a search in the LISP Database of the ITR.
</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. Note
that the mapping used for such a selection is determined by
the Destination EID, used as lookup key in the LISP
Cache of the ITR.
</t>
</list>
</t>
<t> 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 combination of the flags, when the V-bit
is set to 1, are described in <xref target="I-D.ietf-lisp"/>.
As a recall and in summary, Map-Version cannot be used with the
Echo-Nonce feature (E = 1) and the Nonce feature (N = 1), since
they use the same bitfield.
</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 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
<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-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_zero"/> 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.
Furthermore, existing and future mapping distribution
protocol (e.g., ALT <xref target="I-D.ietf-lisp-alt"/>) are able
to carry version numbers without needing any modification.
The same applies to the LISP Map Server
(<xref target="I-D.ietf-lisp-ms"/>), which will still work
without any change since reserved bits are simply ignored.
</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">
<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 xTR B of domain B, while xTR A.2 of
domain A and xTR B of domain B exchange bidirectional traffic.
</t>
<t>
<figure anchor="vtraffic">
<artwork><![CDATA[
+-----------------+ +-----------------+
| Domain A | | Domain B |
| +---------+ | |
| | xTR A.1 |--- | |
| +---------+ \ +---------+ |
| | -------->| xTR B | |
| | -------->| | |
| +---------+ / +---------+ |
| | xTR A.2 |<-- | |
| +---------+ | |
| | | |
+-----------------+ +-----------------+
]]></artwork>
</figure>
</t>
<t>
Obviously in the case of Map-Versioning both xTRs of domain
A must use the same value otherwise the xTR 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 xTRs of domain A send different Loc
Status Bits. In this case either the traffic is disrupted, if
the xTR B trusts the Locator Status Bits, or if xTR 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>
<section title="Map-Versioning and unidirectional traffic">
<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>
<section title="Map-Versioning and interworking">
<t>
Map-Versioning works in the context of interworking
between LISP and IPv4 and IPv6
(<xref target="I-D.ietf-lisp-interworking"/>) in the following
way.
</t>
<t>
The case of proxy-ITR encapsulating packet for LISP sites is
basically the same as the unidirectional traffic case presented
in the previous section. The same rules can be applied.
The only difference that arises is the fact that a proxy-ITR does
not have any mapping, since it just encapsulate packets arriving
from non-LISP site, thus it has no Source Map-Version.
In this case, the proxy-ITR will just put the special value 0
(zero) as Source Map-Version number, while the receiving ETR
will ignore the field.
</t>
</section>
<section title="Graceful RLOC shutdown/withdraw">
<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, because all sites
have updated the mapping, it can be shut down safely.
</t>
</section>
<section title="Map-Version for lightweight LISP implementation">
<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 proposed in the present section is just a case
study and MUST NOT be considered as specification for a
lightweight LISP implementation.
</t>
</section>
</section>
<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 new 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> A thorough security analysis of LISP is documented in
<xref target="I-D.saucez-lisp-security" />.
</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.
Note also that 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.
</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>
<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>
</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 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>
</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>Posted September 2010.
</t>
<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>
</section> <!-- Document Change Log -->
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-23 02:52:58 |