Network Working Group L. Iannone
Internet-Draft TU Berlin - Deutsche Telekom
Intended status: Experimental Laboratories AG
Expires: April 1, 2011 D. Saucez
O. Bonaventure
Universite catholique de Louvain
September 28, 2010
LISP Map-Versioning
draft-ietf-lisp-map-versioning-00.txt
Abstract
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.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 4
3. Definitions of Terms . . . . . . . . . . . . . . . . . . . . . 4
4. EID-to-RLOC Map-Version number . . . . . . . . . . . . . . . . 4
4.1. The special Map-Version 0 . . . . . . . . . . . . . . . . 5
5. Dealing with Map-Version numbers . . . . . . . . . . . . . . . 5
5.1. Handling Destination Map-Version number . . . . . . . . . 6
5.2. Handling Source Map-Version number . . . . . . . . . . . . 7
6. LISP header and Map-Version numbers . . . . . . . . . . . . . 8
7. Map Record and Map-Version . . . . . . . . . . . . . . . . . . 10
8. Benefits and case studies for Map-Versioning . . . . . . . . . 11
8.1. Synchronization of different xTRs . . . . . . . . . . . . 11
8.2. Map-Versioning and unidirectional traffic . . . . . . . . 12
8.3. Map-Versioning and interworking . . . . . . . . . . . . . 13
8.4. Graceful RLOC shutdown/withdraw . . . . . . . . . . . . . 13
8.5. Map-Version for lightweight LISP implementation . . . . . 13
9. Incremental deployment and implementation status . . . . . . . 14
10. Security Considerations . . . . . . . . . . . . . . . . . . . 14
10.1. Map-Versioning against traffic disruption . . . . . . . . 14
10.2. Map-Versioning against reachability information DoS . . . 15
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
13.1. Normative References . . . . . . . . . . . . . . . . . . . 16
13.2. Informative References . . . . . . . . . . . . . . . . . . 16
Appendix A. Estimation of time before Map-Version wrap-around . . 17
Appendix B. Document Change Log . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
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1. Introduction
This document describes the Map-Versioning mechanism used to provide
information on changes in the EID-to-RLOC mappings used in the LISP
([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.
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.
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:
1. The version number assigned to the mapping (contained in the EID-
to-RLOC Database) used to select the source RLOC.
2. The version number assigned to the mapping (contained in the EID-
to-RLOC Cache) used to select the destination RLOC.
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 [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.
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2. Requirements Notation
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 [RFC2119].
3. Definitions of Terms
Map-Version number: An unsigned 12-bits assigned to an EID-to-RLOC
mapping, not including the value 0 (0x000).
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.
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.
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.
4. EID-to-RLOC Map-Version number
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. Appendix A contains a rough estimation
of the wrap-around time for the Map-Version number.
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:
V1 = V2 : This is the exact match case.
V1 < V2 : True if and only if V1 < V2 < (V1 + 2**(N-1)).
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V1 > V2 : True if and only if V1 > V2 > (V1 - 2**(N-1)).
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.
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 Section 4.1).
4.1. The special Map-Version 0
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 [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.
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).
5. Dealing with Map-Version numbers
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.
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:
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o 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.
o 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.
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:
1. 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.
2. In case of bidirectional traffic, the mapping in the local xTR
cache for the source EID is up-to-date.
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 Section 5.1) or to update the mapping in the local
cache (see Section 5.2).
5.1. Handling Destination Map-Version number
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:
1. 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.
2. 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.
3. 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
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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 [I-D.ietf-lisp], while their security is discussed
in [I-D.saucez-lisp-security]. These Map-Request messages should
be rate limited (rate limitation policies are also described in
[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.
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 [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.
For LISP-encapsulated packets with the V-bit set, the Destination
Map-Version can never contain the special value 0. Indeed, as
explained in Section 4.1, 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.
5.2. Handling Source Map-Version number
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:
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1. 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.
2. 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 [I-D.ietf-lisp], including rate limitation
policies.
3. 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.
Otherwise, if the xTR does not have an entry in its cache (e.g.
unidirectional traffic) the Source Map-Version can be safely ignored.
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.
6. LISP header and Map-Version numbers
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.
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
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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 [I-D.ietf-lisp]. In the following example we include
all the headers of a LISP encapsulated packet just for the sake of
clarity.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
V (1 bit): this is the Map-Version bit as defined in
[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.
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
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Database of the ITR.
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.
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 [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.
7. Map Record and Map-Version
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 [I-D.ietf-lisp] and reported here as example.
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 |
+-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Map-Version Number: Map-Version of the mapping contained in the
Record. As explained in Section 4.1 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
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V-bit MUST be set to 0.
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
[I-D.ietf-lisp-alt]) are able to carry version numbers without
needing any modification. The same applies to the LISP Map Server
([I-D.ietf-lisp-ms]), which will still work without any change since
reserved bits are simply ignored.
8. Benefits and case studies for Map-Versioning
In the following sections we provide more discussion on various
aspects and use of the Map-Versioning. Security observations are
instead grouped in Section 10.
8.1. Synchronization of different xTRs
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.
As an example, let's consider the topology of Figure 1 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.
+-----------------+ +-----------------+
| Domain A | | Domain B |
| +---------+ | |
| | xTR A.1 |--- | |
| +---------+ \ +---------+ |
| | -------->| xTR B | |
| | -------->| | |
| +---------+ / +---------+ |
| | xTR A.2 |<-- | |
| +---------+ | |
| | | |
+-----------------+ +-----------------+
Figure 1
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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.
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.
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 Section 7.
8.2. Map-Versioning and unidirectional traffic
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 Figure 2, since
LISP specification do not mandate for ETR to have a mapping for the
source EID.
+-----------------+ +-----------------+
| Domain A | | Domain B |
| +---------+ +---------+ |
| | ITR A |----------->| ETR B | |
| +---------+ +---------+ |
| | | |
+-----------------+ +-----------------+
Figure 2
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.
For what concerns the ETR, it simply checks only the Destination Map-
Version number in the same way as described in Section 5, ignoring
the Source Map-Version number.
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8.3. Map-Versioning and interworking
Map-Versioning works in the context of interworking between LISP and
IPv4 and IPv6 ([I-D.ietf-lisp-interworking]) in the following way.
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.
8.4. Graceful RLOC shutdown/withdraw
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 [I-D.ietf-lisp]), but without actually turning
it off.
Once no more traffic is received by the RLOC, because all sites have
updated the mapping, it can be shut down safely.
8.5. Map-Version for lightweight LISP implementation
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.
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 [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 [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.
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.
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Further, Map-Version can be used to substitute the "clock sweep"
operation described in Section 6.5.1 of [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.
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.
9. Incremental deployment and implementation status
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.
Map-Versioning is currently implemented in OpenLISP
[I-D.iannone-openlisp-implementation].
Note that the reference document for LISP implementation and
interoperability tests remains [I-D.ietf-lisp].
10. Security Considerations
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.
A thorough security analysis of LISP is documented in
[I-D.saucez-lisp-security].
10.1. Map-Versioning against traffic disruption
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.
This does not happen in the case of Map-Versioning. As described in
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Section 5, 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
Section 5, otherwise the packet is simply dropped.
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
Section 10.2).
10.2. Map-Versioning against reachability information DoS
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 [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.
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.
11. IANA Considerations
This document has no actions for IANA.
12. Acknowledgements
The authors would like to thank Pierre Francois, Noel Chiappa, Dino
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Farinacci for their comments and review.
This work has been partially supported by the INFSO-ICT-216372
TRILOGY Project (www.trilogy-project.org).
13. References
13.1. Normative References
[I-D.ietf-lisp]
Farinacci, D., Fuller, V., Meyer, D., and D. Lewis,
"Locator/ID Separation Protocol (LISP)",
draft-ietf-lisp-08 (work in progress), August 2010.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
13.2. Informative References
[I-D.iannone-openlisp-implementation]
Iannone, L., Saucez, D., and O. Bonaventure, "OpenLISP
Implementation Report",
draft-iannone-openlisp-implementation-01 (work in
progress), July 2008.
[I-D.ietf-lisp-alt]
Fuller, V., Farinacci, D., Meyer, D., and D. Lewis, "LISP
Alternative Topology (LISP+ALT)", draft-ietf-lisp-alt-04
(work in progress), April 2010.
[I-D.ietf-lisp-interworking]
Lewis, D., Meyer, D., Farinacci, D., and V. Fuller,
"Interworking LISP with IPv4 and IPv6",
draft-ietf-lisp-interworking-01 (work in progress),
August 2010.
[I-D.ietf-lisp-ms]
Fuller, V. and D. Farinacci, "LISP Map Server",
draft-ietf-lisp-ms-05 (work in progress), April 2010.
[I-D.saucez-lisp-security]
Saucez, D., Iannone, L., and O. Bonaventure, "LISP
Security Threats", draft-saucez-lisp-security-01 (work in
progress), July 2010.
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Appendix A. Estimation of time before Map-Version wrap-around
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 ([I-D.ietf-lisp]).
Alternatively a granularity of minutes can also be used, as for the
TTL of the Map-Reply ([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.
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.
+---------------+--------------------------------------------+
|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 |
+---------------+---------------------+----------------------+
Figure 3: Estimation of time before wrap-around
Appendix B. Document Change Log
o Posted September 2010.
o Added Section "Definitions of Terms".
o Editorial polishing of all sections.
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o Added clarifications in section "Dealing with Map-Version numbers"
for the case of the special Map-Version number 0.
o Rename of draft-iannone-mapping-versioning-02.txt.
Authors' Addresses
Luigi Iannone
TU Berlin - Deutsche Telekom Laboratories AG
Ernst-Reuter Platz 7
Berlin
Germany
Email: luigi@net.t-labs.tu-berlin.de
Damien Saucez
Universite catholique de Louvain
Place St. Barbe 2
Louvain la Neuve
Belgium
Email: damien.saucez@uclouvain.be
Olivier Bonaventure
Universite catholique de Louvain
Place St. Barbe 2
Louvain la Neuve
Belgium
Email: olivier.bonaventure@uclouvain.be
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