Locator/ID Separation Protocol (LISP) Map-Versioning
draft-ietf-lisp-6834bis-08
Network Working Group L. Iannone
Internet-Draft Huawei Technologies France S.A.S.U
Obsoletes: 6834 (if approved) D. Saucez
Intended status: Standards Track INRIA
Expires: September 25, 2021 O. Bonaventure
Universite catholique de Louvain
March 24, 2021
Locator/ID Separation Protocol (LISP) Map-Versioning
draft-ietf-lisp-6834bis-08
Abstract
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 the
transport of 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 optional and transparent to
implementations not supporting this feature, 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 or do not
want to use the mechanism.
This document obsoletes RFC 6834 "Locator/ID Separation Protocol
(LISP) Map-Versioning", which is the initial experimental
specifications of the mechanisms updated by this document.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on September 25, 2021.
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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 Null Map-Version . . . . . . . . . . . . . . . . . . 5
5. Dealing with Map-Version Numbers . . . . . . . . . . . . . . 6
5.1. Handling Destination Map-Version Number . . . . . . . . . 7
5.2. Handling Source Map-Version Number . . . . . . . . . . . 9
6. LISP Header and Map-Version Numbers . . . . . . . . . . . . . 9
7. Map Record and Map-Version . . . . . . . . . . . . . . . . . 10
8. Benefits and Case Studies for Map-Versioning . . . . . . . . 11
8.1. Map-Versioning and Unidirectional Traffic . . . . . . . . 11
8.2. Map-Versioning and Interworking . . . . . . . . . . . . . 12
8.2.1. Map-Versioning and Proxy-ITRs . . . . . . . . . . . . 12
8.2.2. Map-Versioning and LISP-NAT . . . . . . . . . . . . . 13
8.2.3. Map-Versioning and Proxy-ETRs . . . . . . . . . . . . 13
8.3. RLOC Shutdown/Withdraw . . . . . . . . . . . . . . . . . 13
8.4. Map-Version Additional Use Cases . . . . . . . . . . . . 14
9. Security Considerations . . . . . . . . . . . . . . . . . . . 14
10. Deployment Considerations . . . . . . . . . . . . . . . . . . 14
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
12.1. Normative References . . . . . . . . . . . . . . . . . . 16
12.2. Informative References . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
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1. Introduction
This document describes the Map-Versioning mechanism used to provide
information on changes in the EID-to-RLOC (Endpoint ID to Routing
Locator) mappings used in the LISP (Locator/ID Separation Protocol
[I-D.ietf-lisp-rfc6830bis][I-D.ietf-lisp-rfc6833bis]) context to
perform packet encapsulation. The mechanism is totally transparent
to xTRs (Ingress and Egress Tunnel Routers) not supporting or not
using such functionality.
This document obsoletes [RFC6834], which is the initial experimental
specifications of the mechanisms updated by this document.
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.
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 RLOCs). 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 (Ingress Tunnel Router) 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 used to select the
source RLOC (contained in the EID-to-RLOC Database).
2. The version number assigned to the mapping used to select the
destination RLOC (contained in the EID-to-RLOC Map-Cache).
This operation is two-fold. On the one hand, it enables the ETR
(Egress Tunnel Router) receiving the packet to know if the ITR is
using the latest mapping version that any ETR at the destination EID
site would provide to the ITR in a Map-Reply. If this is not the
case, the ETR can send to the ITR a Map-Request containing the
updated mapping or solicit a Map-Request from the ITR (both cases are
already defined in [I-D.ietf-lisp-rfc6833bis]). In this way, the ITR
can update its EID-to-RLOC Map-Cache. On the other hand, it enables
an ETR receiving such a packet to know if it has in its EID-to-RLOC
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Map-Cache the latest mapping for the source EID. If this is not the
case, a Map-Request can be sent.
Considerations about the deployment of LISP Map-Versioning are
discussed in Section 10.
2. Requirements Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Definitions of Terms
This document uses terms already defined in the main LISP
specification ([I-D.ietf-lisp-rfc6830bis],
[I-D.ietf-lisp-rfc6833bis]). Here, we define the terms that are
specific to the Map-Versioning mechanism. Throughout the whole
document, Big Endian bit ordering is used.
Map-Version number: An unsigned 12-bit integer is assigned to an
EID-to-RLOC mapping, not including the value 0 (0x000).
Null Map-Version: The 12-bit null value of 0 (0x000) is not used as
a 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: This Map-Version number of the EID-to-
RLOC mapping is used to select the source address (RLOC) of the
outer IP header of LISP-encapsulated packets.
Destination Map-Version number: This Map-Version number of the EID-
to-RLOC mapping is used to select the destination address (RLOC) of
the outer IP header of LISP-encapsulated packets.
4. EID-to-RLOC Map-Version Number
The EID-to-RLOC Map-Version number consists of an unsigned 12-bit
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 of incrementing by one the older
version number.
The space of version numbers has a circular order where half of the
version numbers are greater (i.e., newer) than the current Map-
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Version number and the other half of the version numbers are smaller
(i.e., older) than the current Map-Version number. In a more formal
way, assuming that we have two version numbers V1 and V2 and that the
numbers are expressed on N bits, the following steps MUST be
performed (in the same order as shown below) to strictly define their
order:
1. V1 = V2 : The Map-Version numbers are the same.
2. V2 > V1 : if and only if
V2 > V1 AND (V2 - V1) <= 2**(N-1)
OR
V1 > V2 AND (V1 - V2) > 2**(N-1)
3. V1 > V2 : otherwise.
Using 12 bits, as defined in this document, and assuming a Map-
Version value of 69, Map-Version numbers in the range [70; 69 + 2048]
are greater than 69, while Map-Version numbers in the range [69 +
2049; (69 + 4096) mod 4096] are smaller than 69.
Map-version numbers are assigned to mappings by configuration. The
initial Map-Version number of a new EID-to-RLOC mapping SHOULD be
assigned randomly, but it MUST NOT be set to the Null Map-Version
value (0x000), because the Null Map-Version number has a special
meaning (see Section 4.1).
Upon reboot, an ETR will use mappings configured in its EID-to-RLOC
Database. If those mappings have a Map-Version number, it will be
used according to the mechanisms described in this document. ETRs
MUST NOT automatically generate and assign Map-Version numbers to
mappings in the EID-to-RLOC Database.
4.1. The Null Map-Version
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.
The Null Map-Version MAY appear in the LISP-specific header as either
a Source Map-Version number (cf. Section 5.2) or a Destination Map-
Version number (cf. Section 5.1). 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 Map-Cache,
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then the ETR MUST NOT compare the received Null Map-Version with the
content of the EID-to-RLOC Map-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.
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 [I-D.ietf-lisp-rfc6833bis]). 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 referred to by the
Map Record MUST either not contain any Map-Version numbers (V bit set
to 0) or, if they contain 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.
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 the Map-Version
number MUST be incremented by 2 (i.e., set to 1 (0x001), 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 Traffic Engineering 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.
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. This is orthogonal to whether or not Map-Versioning
is used. The synchronization problem and its implications on the
traffic are out of the scope of this document.
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
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header. This means that the header needs to contain two Map-Version
numbers:
o The Source Map-Version number of the EID-to-RLOC mapping in the
EID-to-RLOC Database used to select the source RLOC.
o The Destination Map-Version number of the EID-to-RLOC mapping in
the EID-to-RLOC Map-Cache used to select the destination RLOC.
By embedding both the Source Map-Version number and the Destination
Map-Version number, an ETR receiving a LISP packet with Map-Version
numbers can perform the following checks:
1. The ITR that has sent the packet has an up-to-date mapping in its
EID-to-RLOC Map-Cache for the destination EID and is performing
encapsulation correctly.
2. In the case of bidirectional traffic, the mapping in the local
ETR EID-to-RLOC Map-Cache for the source EID is up to date.
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 Section 5.1) or to update the mapping in the local
EID-to-RLOC Map-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
an 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:
1. The packet arrives 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 Map-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.
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
number, and the packet SHOULD be silently dropped.
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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
its EID-to-RLOC Map-Cache containing stale information. The ETR
MAY choose to normally process the encapsulated datagram
according to [I-D.ietf-lisp-rfc6830bis]; however, 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 use the SMR bit or
how to piggyback mappings in Map-Request messages is already
described in [I-D.ietf-lisp-rfc6833bis]. One 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 limiting the rate of Map-Request messages. This is
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.
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 Time To Live
(TTL) (defined in [I-D.ietf-lisp-rfc6833bis]) 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. Such
action is permitted because 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 EID-to-RLOC Map-
Caches of ITRs must have expired. Hence, all ITRs sending traffic
should have refreshed the mapping according to
[I-D.ietf-lisp-rfc6833bis]. If packets with old Map-Version numbers
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.
LISP-encapsulated packets with the V-bit set, when the original
mapping in the EID-to-RLOC Database has the version number set to the
Null Map-Version value, MAY be silently dropped. As explained in
Section 4.1, if an EID-to-RLOC mapping has a Null Map-Version, it
means that ITRs, using the mapping for encapsulation, MUST NOT use a
Map-Version number in the LISP-specific header.
For LISP-encapsulated packets with the V-bit set, when the original
mapping in the EID-to-RLOC Database has the version number set to a
value different from the Null Map-Version value, a Destination Map-
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Version number equal to the Null Map-Version value means that the
Destination Map-Version number MUST be ignored.
5.2. Handling Source Map-Version Number
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
Map-Cache for the source EID, then a check can be performed and the
following cases can arise:
1. The packet arrives with the same Source Map-Version number as
that stored in the EID-to-RLOC Map-Cache. This is the correct
regular case. The ITR has in its EID-to-RLOC Map-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 EID-to-RLOC Map-
Cache. This means that the ETR has in its EID-to-RLOC Map-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
[I-D.ietf-lisp-rfc6833bis], 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 EID-to-RLOC Map-
Cache. Such a case is not valid with respect to the
specifications. Indeed, if the mapping is already present in the
EID-to-RLOC Map-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, the Map-Version in the EID-to-RLOC Map-Cache is the
correct one, while the one carried by the packet is stale. In
this situation, the packet MAY be silently dropped.
If the ETR does not have an entry in the EID-to-RLOC Map-Cache for
the source EID, then the Source Map-Version number can be ignored.
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.
6. LISP Header and Map-Version Numbers
In order for the versioning approach to work, the LISP-specific
header has to carry both the Source Map-Version number and
Destination Map-Version number. This is done by setting the V-bit in
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the LISP-specific header as specified in [I-D.ietf-lisp-rfc6830bis].
When the V-bit is set and the N bit is reset (0), the low-order 24
bits of the first longword are used to transport both the source and
destination Map-Version numbers. In particular, the first 12 bits
are used for the Source Map-Version number and the second 12 bits for
the Destination Map-Version number.
Below is an example of a LISP header carrying version numbers.
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|R|K|K| Source Map-Version |Destination Map-Version|
LISP+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | Instance ID/Locator Status Bits |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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. Section 5.2 describes how to set this value on
transmission and handle it on reception.
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. Section 5.1 describes how to set this
value on transmission and handle it on reception.
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 permissible combinations of the flags when the V-bit is
set to 1 are described in [I-D.ietf-lisp-rfc6830bis].
7. Map Record and Map-Version
To accommodate the proposed mechanism, the Map Records that are
transported in 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 describes a mapping are
used (see [I-D.ietf-lisp-rfc6833bis] and reported here as an example.
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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 |
+-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
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.
8. Benefits and Case Studies for Map-Versioning
In the following sections, we provide more discussion on various
aspects and uses of Map-Versioning. Security observations are
grouped in Section 9.
8.1. 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, for instance, in the case presented in Figure 1, since the
LISP specification does not mandate that the ETR have a mapping for
the source EID.
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+-----------------+ +-----------------+
| Domain A | | Domain B |
| +---------+ +---------+ |
| | ITR A |----------->| ETR B | |
| +---------+ +---------+ |
| | | |
+-----------------+ +-----------------+
Figure 1: Unidirectional traffic between LISP domains.
In the case of the ITR, the ITR is able to put both the source and
destination version number in the LISP header, since the Source Map-
Version number is in the ITR's database, while the Destination Map-
Version number is in the ITR's cache.
In the case of the ETR, the ETR simply checks only the Destination
Map-Version number in the same way as that described in Section 5,
ignoring the Source Map-Version number.
8.2. Map-Versioning and Interworking
Map-Versioning is compatible with the LISP interworking between LISP
and non-LISP sites as defined in [RFC6832]. LISP interworking
defines three techniques to make LISP sites and non-LISP sites,
namely Proxy-ITR, LISP-NAT, and Proxy-ETR. The following text
describes how Map-Versioning relates to these three mechanisms.
8.2.1. Map-Versioning and Proxy-ITRs
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. Figure 2). This case is very
similar to the unidirectional traffic case described in Section 8.1;
hence, similar rules apply.
+----------+ +-------------+
| LISP | | non-LISP |
| Domain A | | Domain B |
| +-------+ +-----------+ | |
| | ETR A |<-------| Proxy ITR |<-------| |
| +-------+ +-----------+ | |
| | | |
+----------+ +-------------+
Figure 2: Unidirectional traffic from non-LISP domain to LISP domain.
The main difference is that a Proxy-ITR does not have any mapping,
since it just encapsulates packets arriving from the non-LISP site,
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and thus cannot provide a Source Map-Version. In this case, the
proxy-ITR will just put the Null Map-Version value as the Source Map-
Version number, while the receiving ETR will ignore the field.
With this setup, LISP Domain A is able to check whether or not the
PITR is using the latest mapping.
8.2.2. Map-Versioning and LISP-NAT
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.
8.2.3. Map-Versioning and Proxy-ETRs
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. Figure 3). One of the main reasons to deploy PETRs
is to bypass uRPF (Unicast Reverse Path Forwarding) checks on the
provider edge.
+----------+ +-------------+
| LISP | | non-LISP |
| Domain A | | Domain B |
| +-------+ +-----------+ | |
| | ITR A |------->| Proxy ETR |------->| |
| +-------+ +-----------+ | |
| | | |
+----------+ +-------------+
Figure 3: Unidirectional traffic from LISP domain to non-LISP domain.
A Proxy-ETR does not have any mapping, since it just decapsulates
packets arriving from the LISP site. In this case, the ITR will just
put the Null Map-Version value as the Destination Map-Version number,
while the receiving Proxy-ETR will ignore the field.
With this setup, the Proxy-ETR is able to check whether or not the
mapping has changed.
8.3. RLOC Shutdown/Withdraw
Map-Versioning can also be 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 (via
the R bit in the Map Record; see [I-D.ietf-lisp-rfc6833bis]), but
without actually turning it off.
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Once no more traffic is received by the RLOC, it can be shut down
gracefully, because all sites actively using the mapping have updated
it.
8.4. Map-Version Additional Use Cases
The use of Map-Versioning can help in developing a lightweight
implementation of LISP. However, this comes with the price of not
supporting the Loc Status Bit, which may be 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 ([I-D.ietf-lisp-rfc6830bis]). . When a new RLOC is added to a
mapping, a new mapping with a new Map-Version number will be issued,
and since the old locators are still valid, the transition will occur
with no disruptions. The same applies for the case where an RLOC is
withdrawn. The use of Map-Versioning allows to avoiding using the
"use-LSB" timer (cf. [I-D.ietf-lisp-rfc6830bis]) since it allows to
check whether or not the mapping has been updated.
9. Security Considerations
Attackers can try to trigger a large number of Map-Requests by simply
forging packets with random Map-Versions. The Map-Requests are rate-
limited as described in [I-D.ietf-lisp-rfc6833bis]. With Map-
Versioning it is possible to filter invalid version numbers before
triggering a Map-Request, thus helping to reduce the effects of DoS
attacks. However, it might not be enough to really protect from a
DDoS attack.
Robustness of the Map-Versioning mechanism leverages on a trusted
Mapping Distribution System. A thorough security analysis of LISP is
documented in [RFC7835].
As specified in [I-D.ietf-lisp-rfc6830bis], Map-Versioning MUST NOT
be used over the public Internet and SHOULD only be used in trusted
and closed deployments.
10. Deployment Considerations
Even without Map-Versioning, LISP requires ETRs to announce the same
mapping for the same EID-Prefix to a requester. Map-Versioning does
not require additional synchronization mechanisms as 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, and traffic disruptions. It is the same without Map-
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Versioning, with ETRs that have to reply with the same mapping;
otherwise, the same problems arise.
There are two ways Map-Versioning is helpful with respect to the
synchronization problem. On the one hand, assigning version numbers
to mappings helps in debugging, since quick checks on the consistency
of the mappings on different ETRs can be done by looking at the Map-
Version number. On the other hand, Map-Versioning can be used to
control the traffic toward ETRs that announce the latest mapping.
As an example, let's consider the topology of Figure 4 where ITR A.1
of Domain A is sending unidirectional traffic to Domain B, while A.2
of Domain A exchanges bidirectional traffic with Domain B. In
particular, ITR A.2 sends traffic to ETR B, and ETR A.2 receives
traffic from ITR B.
+-----------------+ +-----------------+
| Domain A | | Domain B |
| +---------+ | |
| | ITR A.1 |--- | |
| +---------+ \ +---------+ |
| | ------->| ETR B | |
| | ------->| | |
| +---------+ / | | |
| | ITR A.2 |--- -----| ITR B | |
| | | / +---------+ |
| | ETR A.2 |<----- | |
| +---------+ | |
| | | |
+-----------------+ +-----------------+
Figure 4: Example topology.
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.
The same problem can, however, arise without Map-Versioning, for
instance, if the two ITRs of Domain A send different Locator Status
Bits. In this case, either the traffic is disrupted if ETR B trusts
the Locator Status Bits, or if ETR B does not trust the Locator
Status Bits it will start sending Map-Requests to confirm each change
in 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-
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Versioning will take advantage of it automatically, since it is
included in the Record format, as described in Section 7.
11. IANA Considerations
This document includes no request to IANA.
12. References
12.1. Normative References
[I-D.ietf-lisp-rfc6830bis]
Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A.
Cabellos-Aparicio, "The Locator/ID Separation Protocol
(LISP)", draft-ietf-lisp-rfc6830bis-36 (work in progress),
November 2020.
[I-D.ietf-lisp-rfc6833bis]
Farinacci, D., Maino, F., Fuller, V., and A. Cabellos-
Aparicio, "Locator/ID Separation Protocol (LISP) Control-
Plane", draft-ietf-lisp-rfc6833bis-30 (work in progress),
November 2020.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
12.2. Informative References
[RFC6832] Lewis, D., Meyer, D., Farinacci, D., and V. Fuller,
"Interworking between Locator/ID Separation Protocol
(LISP) and Non-LISP Sites", RFC 6832,
DOI 10.17487/RFC6832, January 2013,
<https://www.rfc-editor.org/info/rfc6832>.
[RFC6834] Iannone, L., Saucez, D., and O. Bonaventure, "Locator/ID
Separation Protocol (LISP) Map-Versioning", RFC 6834,
DOI 10.17487/RFC6834, January 2013,
<https://www.rfc-editor.org/info/rfc6834>.
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[RFC7835] Saucez, D., Iannone, L., and O. Bonaventure, "Locator/ID
Separation Protocol (LISP) Threat Analysis", RFC 7835,
DOI 10.17487/RFC7835, April 2016,
<https://www.rfc-editor.org/info/rfc7835>.
Authors' Addresses
Luigi Iannone
Huawei Technologies France S.A.S.U
EMail: luigi.iannone@huawei.com
Damien Saucez
INRIA
EMail: damien.saucez@inria.fr
Olivier Bonaventure
Universite catholique de Louvain
EMail: olivier.bonaventure@uclouvain.be
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