Network Working Group S. Brim
Internet-Draft N. Chiappa
Intended status: Experimental D. Farinacci
Expires: May 17, 2008 V. Fuller
D. Lewis
D. Meyer
November 14, 2007
LISP-CONS: A Content distribution Overlay Network Service for LISP
draft-meyer-lisp-cons-03.txt
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Abstract
The Content distribution Overlay Network Service for LISP (LISP-CONS)
is a protocol for distributing identifier-to-locator mappings for the
Locator/ID Separation Protocol (LISP). LISP-CONS is not a routing
protocol. LISP-CONS is designed to scale by using a hierarchical
content distribution system comprised of Tunnel Routers, Content
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Access Resources, and Content Distribution Resources.
Table of Contents
1. Requirements Notation . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 4
3.1. LISP-CONS Name Spaces . . . . . . . . . . . . . . . . . . 5
3.2. LISP-CONS Network Elements . . . . . . . . . . . . . . . . 5
3.3. Relationship Between LISP-CONS Network Elements . . . . . 7
4. Overview of Operation . . . . . . . . . . . . . . . . . . . . 7
5. The LISP-CONS Protocol . . . . . . . . . . . . . . . . . . . . 10
5.1. Building the LISP-CONS Database . . . . . . . . . . . . . 10
5.2. Querying the LISP-CONS Database . . . . . . . . . . . . . 11
5.3. Maintaining the LISP-CONS Database . . . . . . . . . . . . 13
5.3.1. An EID-Prefix Is Administratively Removed From The
Infrastructure . . . . . . . . . . . . . . . . . . . . 13
5.3.2. A CAR's Connectivity Changes . . . . . . . . . . . . . 14
5.3.3. A CAR Becomes Unreachable . . . . . . . . . . . . . . 15
5.3.4. A CDR Becomes Unreachable . . . . . . . . . . . . . . 15
6. LISP-CONS Message Types . . . . . . . . . . . . . . . . . . . 16
7. Operational Considerations . . . . . . . . . . . . . . . . . . 17
8. LISP-CONS and Locator Reachability . . . . . . . . . . . . . . 17
9. LISP-CONS and Mobility . . . . . . . . . . . . . . . . . . . . 17
10. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 17
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18
12. Security Considerations . . . . . . . . . . . . . . . . . . . 18
12.1. Apparent LISP-CONS Vunerabilities . . . . . . . . . . . . 19
12.2. Survey of LISP-CONS Security Mechanisms . . . . . . . . . 19
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
14.1. Normative References . . . . . . . . . . . . . . . . . . . 20
14.2. Informative References . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21
Intellectual Property and Copyright Statements . . . . . . . . . . 23
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1. 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].
2. Introduction
The Content distribution Overlay Network Service for LISP, or LISP-
CONS, is a control-plane protocol for distributing identifier-to-
locator mappings for the Locator/ID Separation Protocol (LISP)
[LISP]. The properties of such a "locator/id split" have been
discussed in depth in various venues dating back to [CHIAPPA] and
[RFC1498], and as such will not be reviewed here. Rather, the reader
is referred to the above references for an outline of the various
benefits that may be realized by separating the functionality of IP
addresses into separate Endpoint Identifier and Routing Locator name
spaces.
LISP-CONS operates on a distributed Endpoint Identifier-to-Routing
Locator (EID-to-RLOC) database. This database is distributed among
the authoritative Answering Content Access Resources (Answering-CAR).
An Answering-CAR (aCAR) advertises "reachability" for its EID-to-RLOC
mappings through a hierarchical network of Content Distribution
Resources (CDRs) (but importantly, not the mapping itself), and
responds to mapping requests from the system. A CAR may also request
mappings from the system (this a Querying-CAR, or qCAR). Ingress
Tunnel Routers (ITRs) connect to one or more qCARs to query the
system for EID-to-RLOC bindings; the qCAR then queries the system on
behalf of the ITR. These queries follow the overlay network to the
authoritative aCAR, which responds with the mapping. This response
may then be cached by the 'local' CAR. Finally, note that neither a
qCAR or aCAR need to hold the entire EID-to-RLOC database. Rather,
the EID-to-RLOC translations are explicitly pulled by the ITRs by
querying one or more of its connected qCARs.
Note that LISP-CONS is not designed for the "fast-mobility" case.
That is, it is envisioned that the mappings distributed by LISP-CONS
are reasonably static. LISP-CONS is also not designed to carry
Locator Reachability status information; see [LISP] for details on
how LISP determines locator reachability.
LISP-CONS seeks to control the "state * rate" scaling properties of
the mapping service by first observing that the host mapping state is
likely to be quite large (some estimates put the size of this
database to be on the order of 10^10 hosts). As a result, even with
aggressive aggregation, the "rate" of change of the mapping database
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must be kept small. LISP-CONS manages the rate problem by
distributing highly aggregated information about the location of the
EID-to-RLOC mappings (which are assumed to change at low frequency)
over a peering network. The peering network is comprised of ITRs,
CARs and CDRs.
In summary, LISP-CONS is a hybrid "push/pull" protocol in which
information about the existence of a particular mapping is "pushed"
at the higher levels of the aggregation hierarchy, while the actual
EID-to-RLOC mappings are "pulled" from the network elements at the
lowest level of the hierarchy. In particular, LISP-CONS carries
mapping requests and replies to and from the lowest level of the
hierarchy where the EID-to-RLOC mappings reside.
While this draft focuses on a router-based solution, there is no
architectural reason that LISP-CONS functionality could not be
implemented in other devices (i.e., hosts). However, in keeping with
the architectural direction taken by the LISP data-plane proposal
[LISP], LISP-CONS is based on the the theory that building the
solution into the network should facilitate incremental deployment of
the technology on the Internet. In order to minimize the required
investment in deployment of new hardware, it is assumed that much, if
not all, the initial implementation will be in routers. Finally,
while the detailed protocol specification and examples in this
document assume IP version 4 (IPv4), there is nothing in the design
that precludes the use of the same techniques and mechanisms for
IPv6.
The remainder of this document is organized as follows: Section 3
provides the set of definitions that are used in this document, and
Section 4 provides an overview of LISP-CONS operation. Section 5
describes the LISP-CONS protocol, and Section 6 provides details of
the LISP-CONS message types. Section 7 outlines operational
considerations, Section 8 discusses locator reachability, and
Section 9 considers the interaction of LISP-CONS with mobile nodes.
Section 12 outlines security considerations for LISP-CONS.
Finally, this proposal (as well as the LISP data-plane proposal) was
stimulated by the problem statement effort at the IAB Routing and
Addressing Workshop (RAWS) [I-D.iab-raws-report], which took place in
Amsterdam in October 2006.
3. Definition of Terms
The LISP-CONS protocol operates on two name spaces and is comprised
of four network elements. This section provides high-level
definitions of the LISP-CONS name spaces, network elements, and
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message types.
3.1. LISP-CONS Name Spaces
Endpoint ID (EID): A 32- or 128-bit value used in the source and
destination fields of the first (most inner) LISP header of a
packet. A packet that is emitted by a system contains EIDs in its
headers and and LISP headers are prepended only when the packet
hits an Ingress Tunnel Router (ITR) on the data path to the
destination EID.
In LISP-CONS, EID-prefixes MUST BE assigned in a hierarchical
manner (in power-of-two or larger chunks) such that they can be
aggregated either by Content Access Resources or Content
Distribution Resources (see below). In addition, a site may have
site-local structure in how EIDs are topologically organized
(subnetting) for routing within the site; this structure is not
visible to the global routing system.
EID-Prefix Aggregate: A set of EID-prefixes said to be aggregatable
in the [RFC4632] sense. That is, an EID-Prefix aggregate is
defined to be a single contiguous power-of-two EID-prefix block.
Such a block is characterized by a prefix and a mask.
Routing Locator (RLOC): The IP address of an egress tunnel router
(ETR). It is the output of a EID-to-RLOC mapping lookup. An EID
maps to one or more RLOCs. Typically, RLOCs are numbered from
topologically-aggregatable blocks that are assigned to a site at
each point to which it attaches to the global Internet; where the
topology is defined by the connectivity of provider networks,
RLOCs can be thought of as Provider Aggregatable (PA) addresses.
EID-to-RLOC Mapping: A binding between and EID and the RLOC-set
that can be used to reach the EID. We use the term "mapping" in
this document to refer to a EID-to-RLOC mapping.
3.2. LISP-CONS Network Elements
LISP-CONS consists of the four network element types described below.
Peering connections between these element types use RLOCs so that the
underlying routing system can keep the LISP-CONS peering connections
up (i.e., to avoid circular dependencies on the mapping system).
Each peering connection is required to be configured with a keyed-
hash message authentication code (HMAC) key. A connection MUST NOT
be established without the TCP HMAC option included.
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Content Distribution Resource (CDR): A CDR provides aggregation of
EID prefix lists, propagation of EID-prefix lists to parent CDRs,
and routing of mapping requests to and from CARs.
There may be several levels of aggregation of CDRs. CDRs do not
themselves carry EID prefix to RLOC mappings. CDRs are arranged
in a hierarchical manner in order to enable aggressive aggregation
of EID-prefixes.
Content Access Resource (CAR): A CAR fills one or both of the
following roles:
Answering-CAR (aCAR): A CAR is the source of authority for one or
more EID prefix to RLOC mappings which which it has been
administratively configured, and responds to Map Requests for
these EID-to-RLOC mappings. Each aCAR provides to parent CDRs
a list of prefixes that it is responsible for, but not the
mappings themselves.
In particular, aCARs peer with CDRs to propagate aggregated
information about how to find a particular EID-to-RLOC mapping
upward (but importantly, not the mapping itself). However,
aCARs do not peer with other CARs. The primary difference
between the aCAR and CDR is that a CAR maintains two databases:
A EID-to-RLOC mapping database, and a EID-prefix database. A
CDR maintains only an EID-prefix database.
Querying-CAR (qCAR): A CAR that generates Map-Request messages on
behalf of one or more of its ITR peers (see below). Note that
qCAR has peering connections with ITRs whereas an aCAR does not
have to. Finally, both functionalities (qCAR and aCAR) MAY be
co-located in the same device. In particular, qCAR MUST also
be an aCAR, while an aCAR need not be a qCAR.
Egress Tunnel Router (ETR): A router that accepts an IP packet where
destination address in the "outer" IP header is one of its own
RLOCs. The router strips the "outer" header and forwards the
packet based on the next IP header found. In general, an ETR
receives LISP-encapsulated IP packets from the Internet on one
side and sends decapsulated IP packets to site end-systems on the
other side.
Ingress Tunnel Router (ITR): A router which accepts an IP packet
with a single IP header (more precisely, an IP packet that does
not contain a LISP header). The router treats this "inner" IP
destination address as an EID and performs an EID-to-RLOC mapping
lookup. The router then prepends an "outer" IP header with one of
its globally-routable RLOCs in the source address field and the
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result of the mapping lookup in the destination address field.
Note that this destination RLOC may be an intermediate, proxy
device that has better knowledge of the EID-to-RLOC mapping
closest to the destination EID. In general, an ITR receives IP
packets from site end-systems on one side and sends LISP-
encapsulated IP packets toward the Internet on the other side.
ITRs may also have TCP connections to qCARs in order to send
mapping requests and receive replies (noting that a qCAR, an aCAR,
and an ITR may be co-located).
3.3. Relationship Between LISP-CONS Network Elements
Each LISP-CONS device is known by a single identifier, which is used
for peering from all peers, and in path-vector (PV) lists. This
identifier MAY be an IP address. An implementation SHOULD use a
loopback address for this purpose. Note that this address MUST be
routable by the core routing system.
LISP-CONS network elements peer with each other in one of three
peering relationships: parent, child, or sibling. The relationship
is carried in the LISP-CONS OPEN message (see [LISP]). The permitted
peering relationships are as follows:
o ITRs exist at lowest (unnumbered) level in the peering hierarchy,
and peer only with one or more CARs. An ITR MUST NOT peer with
another ITR or with a CDR.
o CARs exist at level 0 in the peering hierarchy, and peer only with
parent CDRs or with a child ITR. A CAR MUST NOT peer with another
CAR; this rule allows the aCARs to aggregate EID prefixes as low
in the hierarchy as possible. Note that this rule also means that
mapping requests and replies are routed over the peering topology,
not directly between the CARs.
o CDRs exist at level 1 (and above) and aggregate EID-prefixes learn
from its aCAR peerings. When a two CDRs start their peering
connection, if one is a parent, the other MUST BE a child.
Otherwise, they both MUST BE siblings.
o If any of these checks fail, the peering connection MUST NOT be
established.
4. Overview of Operation
LISP-CONS constructs a multi-level content distribution overlay which
achieves scalability by imposing a strict aggregation hierarchy on
the participating elements. The LISP-CONS hierarchy consists of ITRs
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the bottom of the hierarchy, CARs at level 0, and CDRs at levels 1
and above; this is depicted in Figure 1. Each level of the hierarchy
is a strict tree. That is, there are no transit loops in the
hierarchy; redundancy is achieved by meshing CDR connectivity within
in a single level of the hierarchy, and the LISP-CONS protocol
assures that message flow is loop-free.
In LISP-CONS, the EID-to-RLOC mappings are held in the aCARs, while
the CDRs maintain information about how to find the aCAR holding a
particular EID-to-RLOC mapping. That is, the Push-Add and Push-
Delete messages (see [LISP]) only contain EID-prefixes (i.e.,
Locator-sets are not included in these messages and are not stored in
the CDRs).
In general, LISP-CONS uses network element redundancy to avoid
mapping database inconsistencies that may arise in those cases in
which a CAR or CDR crashes. Similarly, connectivity outages are
avoided by configuring a redundant underlying topology.
+----------------+
| CDR ------ CDR |
+--|----------|--+
/ \
/ \
+----------------+ +----------------+
| CDR ------ CDR | | CDR ------ CDR | (CDR-mesh at level 2)
+--|----------|--+ +--|----------|--+
| | | |
| | | |
+---|----------|----+ +---|----------|---+
| CDR ------ CDR | | CDR ------ CDR |
| | | | | | | | (CDR-Mesh at level 1)
| | | | | | | |
| CDR ------ CDR | | CDR ------ CDR |
+---|----------|----+ +---|----------|---+
| | | |
| | | |
| | | |
qCAR aCAR aCAR aCAR
/ \ / \
/ \ / \
ITR ITR ITR ITR
Figure 1: LISP-CONS Hierarchy
Figure 2 depicts the details of the first three levels of hierarchy.
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Note that there are no horizontal TCP connections between the ITRs or
between the CARs. Note that qCARs (abbreviated "Req-CAR") peer with
the ITRs, while the aCARs may not. The CDRs at level 1 are meshed so
that the two aCARs can aggregate to the same mesh level.
Note that to avoid request and reply black-holes, all CDRs that are
responsible for a segment of the address space must be siblings
(i.e., at the same level).
CDR --- CDR (level-1)
|\ /|
| \ / |
| \ / |
| X |
| / \ |
| / \ |
|/ \|
CAR CAR (level-0)
|\ /|
| \ / |
| \ / |
| X |
| / \ |
| / \ |
|/ \|
ITR ITR
Figure 2: LISP-CONS Hierarchy Detail
LISP-CONS operates as follows: An aCAR receives EID-to-RLOC mappings
by administrative configuration. The aCARs aggregate these EID-
prefixes into power-of-two less specific EID-prefixes, and "push" the
aggregated EID-prefixes to their (parent) CDRs in Push-Add messages
(see [LISP]). CDRs then flood the Push-Add messages to their sibling
CDRs. Note that the Push messages contain EID-prefix reachability
information, not locator sets.
If a CDR is a child, it then pushes the aggregate for the EID-prefix
(i.e., the aggregate that "covers" the EID-prefix) to its parent
CDRs. This CDR MUST also originate the default EID-prefix 0.0.0.0/0
or 0::0/0 (this allows Requests and Replies to flow up and down the
aggregation hierarchy). This default is contained within the level
of the sibling mesh. Note that aggregates MUST only be generated
when the components of the aggregate are all longer prefixes than the
aggregate (and importantly, NOT equal in length). For example, a CDR
MUST NOT generate an aggregate such as A.B.0.0/16 if it has not heard
a A.B.*.0/24 from either a child or sibling peer.
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When an ITR needs a mapping, it sends a Map-Request message to its
directly connected qCARs. If any of those CARs have cached the
requested mapping, the result is immediately returned to the ITR.
Otherwise, the Map-Request message is routed through the CDR
hierarchy to the aCAR which holds the mapping. That CAR then returns
the mapping in a Map-Reply message (which is routed over the peering
topology) to the qCAR, which then forwards it on to the requesting
ITR.
Finally, note that this type of advertisement hierarchy allows EID
lookups to have lower Round Trip Times (RTTs) when the EID-prefix is
"close" (in the EID allocation hierarchy) to the site's attached CAR.
However, for scalability reasons, a request may have to travel extra
hops to get an EID-prefix that can only be obtained by going up the
tree (and in the worse case, by going to the top of the hierarchy and
down to the aCAR that hold the mapping).
5. The LISP-CONS Protocol
This section describes the LISP-CONS protocol in detail, starting
with how LISP-CONS builds a distributed mapping database, how an ITR
queries the database, and how the database is maintained.
LISP-CONS operates on three different data structures:
EID-to-RLOC Database: The EID-to-RLOC mapping database, which is
administratively configured and held in the aCARs.
Mapping Cache: The Mapping Cache (hereafter cache) is the result of
a Map-Request and is stored in the ITRs and qCARs.
EID-Prefix Table: The EID-Prefix table is used to route Map-Requests
and Map-Replies in the overlay network. It is stored only by
CDRs, and associates an EID-prefix with a 64-bit sequence number,
a path-vector, and a priority and weight (to facilitate later
aggregation, if possible).
5.1. Building the LISP-CONS Database
When an aCAR is configured with an EID-to-RLOC mapping, it checks to
see if it can aggregate the just learned EID-prefix with any of the
other EID-prefixes it has been configured with. The CAR then sends
("pushes") the EID-prefix (or an aggregate, if possible) to its
parent CDR in a Push-Add message.
An aCAR generates an aggregate when it has at least one more specific
prefix that matches the aggregate. A more specific prefix of an
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aggregate is when the high-order bits of the more-specific prefix and
the high-order bits of the aggregate are the same. The number of
bits tested is the mask-length of the aggregate.
When a more-specific prefix is added to the EID-prefix table, the
corresponding aggregate is sent in a Push-Add message from a child
peer to a parent peer in a different level.
Push-Add messages contain an EID-prefix, and Originator Address, a
64-bit sequence number, and a PV that records the path the message
took in the CDR level (see [LISP]). Note that the Originator Address
is an EID used to route a Reply back to the requesting ITR The PV
list will always contain Locators.
When a CDR receives a Push-Add message, it first checks to see if the
sequence number for the EID-prefix is numerically larger than what it
has stored for the EID-prefix. If it is not, the message is dropped.
Otherwise, the CDR next checks for its own address in the PV. If it
exists, the message is discarded. Otherwise, the CDR stores EID-
prefix and the associated PV. Note that the CDR can store all
different combination of PVs or just the shortest path ones. If the
CDR has one or more parent peerings configured (i.e., the CDR is a
child), it will aggregate this EID-prefix with other EID-prefixes
into a more coarse EID-prefix. The CDR does not need to advertise
anything to lower-level CDRs because child peers will auto-generate a
default EID-prefix into their level simply due to having a child-
parent peering relationship.
When a CDR sends a Push-Add message to a parent, the stored PV is not
propagated to the parent in the aggregated EID-prefix; rather, it
includes a one element PV which contains the address of the CDR
originating the "aggregated push". It also includes a new sequence
number, indicating that this is a different EID-prefix than the ones
it has stored.
Finally, if a CDR is a child, it pushes a "EID-default" to its
siblings. This Push message has EID-prefix 0.0.0.0/0 or 0::0/0 and a
PV containing the address of the CDR that is sourcing the default.
5.2. Querying the LISP-CONS Database
Map Requests are routed along the LISP-CONS multi-level topology from
requesting ITR to aCAR holding the requested mapping. The Map-
Request message includes a PV which records the route traversed by
the Map-Request message. This PV is used to control request routing
and for debugging purposes.
When an ITR wants to query the LISP-CONS database for a mapping, it
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prepares a Map-Request message, which is sent to one of its directly
connected qCAR(s). The Map-Request message is routed over the
peering topology to the aCAR that holds the mapping. If the qCAR has
cached the mapping (perhaps from a previous request), in which case
it returns the mapping immediately.
When a qCAR receives a Map-Request from from an ITR, it MAY respond
immediately if it has the cached requested mapping. Otherwise, it
MUST forward the Map-Request message to its parent CDRs. This CAR is
identified by the Originator address in the Map-Request message (see
[LISP]). The Originator address allows a replying CDR to forward a
No-Map message (see [LISP]) back to the qCAR. This case arises when
source-site is LISP-enabled (i.e., there is an ITR deployed), but the
destination-site has not deployed LISP yet so there is no ETR.
When a Map-Request arrives at a CDR, the CDR first scans its PV for
its address. If its address is present, it drops the packet. If its
address is not present, it consults its EID-prefix table for the
longest match "next-hop" towards the aCAR holding the mapping for the
prefix. If a next-hop is found, the CDR appends its address to the
PV, and forwards the Request to the next-hop.
When a Map-Request arrives at a CDR which cannot route it, a LISP-
CONS No-Map message (see [LISP]) MUST BE sent back to the qCAR. This
No-Map message is a signal that indicates that there is no mapping
for the requested EID in the system, and is immediately communicated
to the ITR.
When a Map-Request message arrives at an aCAR, it first queries its
mapping database for the EID contained in the Map-Request message.
If the mapping is found, it constructs a Map-Reply message (see
[LISP]) containing the EID, the corresponding RLOC-set, and an PV
containing its address appended to the reverse of the received PV.
The CAR then sends the Map-Reply message over the peering topology to
the qCAR (i.e., to the Originating CAR EID-Prefix in the Map-Request
message).
If no mapping is found, the aCAR sends a Map-Reply with the requested
EID and a Locator count of 0 back to qCAR. This creates a negative
cache entry in the requesting ITR.
In LISP-CONS, the PV for Map-Request and Map-Reply messages are
preserved across the hierarchy, while the PV lists carried in Push-
Add and Push-Delete messages are not. As a result, LISP-CONS also
has cross-level loop suppression.
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5.3. Maintaining the LISP-CONS Database
While LISP-CONS is not a routing protocol (and as such when peering
connections go down EID-prefix entries are not immediately withdrawn
from the local EID-prefix table), it does uses a link-state-like
sequence number scheme to detect changes in topology. Similarly,
LISP-CONS uses a path vector scheme to detect and suppress message
looping. There are four database maintenance cases to consider:
o An EID-Prefix Is Administratively Removed From The Infrastructure
(Section 5.3.1)
o A CAR's Connectivity Changes (Section 5.3.2)
o A CAR Becomes Unreachable (Section 5.3.3)
o A CDR Becomes Unreachable (Section 5.3.4)
Each case is considered below.
5.3.1. An EID-Prefix Is Administratively Removed From The
Infrastructure
EID-prefix mappings are removed from the LISP-CONS infrastructure by
administrative configuration at the aCAR that was configured with the
mapping. The CAR queries its EID-prefix database for the mapping.
If no match for the EID-prefix exists, no further action is taken.
When all the more-specific prefixes that matches the aggregate are
removed from the EID-prefix table, the aggregate is sent in a Push-
Delete message from a child peer to a parent peer in a different
level. The Push-Delete message behaves exactly like the Push-Add
message, except that it removes the corresponding state along its
path(s).
When a Push-Delete message arrives at a CDR, the CDR checks for its
own address in the PV. If it exists, the message is discarded.
Otherwise, the CDR queries its EID-prefix database for the EID-prefix
in the received Push-Delete message. If it finds a matching entry,
it removes the entry from its database, appends its address to the
PV, and forwards the message to its siblings.
If the CDR is a child, it checks to see if the EID-prefix in the
Push-Delete message is the last in an aggregate it had previously
pushed to its parent CDR. If not, no further action is taken.
Otherwise, the CDR computes a new aggregate (minus the prefix from
the Push-Delete), sends a Push-Delete for the old aggregate to its
parent, and sends a Push-Add with the new aggregate to its parent
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CDR.
5.3.2. A CAR's Connectivity Changes
Changes in CAR connectivity are signaled by changes in the sequence
numbers in a Push-Add messages. For example, in Figure 3, consider
the case in which the D<->B TCP connection breaks. In this case, D
sends a Push-Add with EID-Prefix EID/(n-1), sequence number, S+1, and
path vector [D] (denoted push(EID/(n-1), S+1, [D])) to C. C
aggregates the pieces of EID and forwards push(EID/n,S+1,[C,D]) to B.
Now, before the failure, B had an entry in its EID-prefix table for
EID/n with sequence number S and PV [D]. Since B sees a new push
message originated by D with sequence number S+1, it knows the
previous entry (EID/n,S,[D]) is no longer valid.
Similarly, A will see push messages with both [C,D] and [B,C,D] and
with sequence number S+1, so it knows the existing entries ([B,D] and
[C,B,D], with sequence number S) are both obsolete.
A
/ \
^ / \ ^
| / \ |
push(EID/n,S,[B,C,D]) | / \ | push(EID/n,S,[C,D])
/ CDR \
push(EID/n,S,[A,C,D]) | / mesh \ | push(EID/n,S,[A,B,C,D])
\|/ / \ \|/ (will be discarded)
/ \
/ \
B-----------------------C
\ push(EID/n,S,[C,D]) /
^ \ <--------- / ^
| \ / |
push(EID/n,S,[D]) | \ / | push(EID/n,S,[D])
| \ / |
\ /
\ /
D (CAR) Configure EID/(n-1), RLOC-set
|
|
|
|
|
F (ETR)
Figure 3: Sequence Number Processing
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5.3.3. A CAR Becomes Unreachable
If the TCP connection between a CAR its peer CDR drops, a timer
associated with the EID-prefix received from the CAR in the Push-Add
message is started. The timer, called the CAR-CDR-TCP-TIMER, is set
to a default value of 60 minutes.
If the TCP connection comes back up before the timer expires, the
timer is stopped and no further action is taken.
If the timer expires, the CDR builds a Push-Delete message for each
EID-prefix it received from the aCAR, and sends the Push-Delete to
its siblings. The Push-Delete message contains the EID-prefix to be
removed, a sequence number, and PV containing only the CDR's address.
If the CDR also has a parent peering, it checks to see if any of the
EID-prefixes it received from a child peering were the last more
specific prefix in an aggregate it previously pushed to a parent CDR.
If not, no further action is taken. If so, it sends a Push-Delete
for the aggregate to its parent(s). In either case, the CDR deletes
the entries received from the failed CAR from its EID-prefix table.
5.3.4. A CDR Becomes Unreachable
There are three cases to consider here: A sibling CDR peering goes
down, a parent peering goes down, and an child peering goes down.
Each is considered below.
5.3.4.1. A Sibling CDR Becomes Unreachable
When the TCP connection drops between a CDR and a sibling CDR, a
timer associated with the EID-prefixes received from the sibling CDR
in the Push-Add message is started. This timer, called CDR-SIBLING-
TCP-TIMER, defaults to TBD.
If the TCP connection comes back up before the timer expires, the
timer is stopped and no further action is taken.
If the timer expires, the CDR builds a Push-Delete message for each
EID-prefix it received from the CDR, and sends the Push-Delete to its
siblings. The Push-Delete message contains the EID-prefix to be
removed, a sequence number, and PV containing only the CDR's address.
If the CDR also has a parent peering, it checks to see if any of the
EID-prefixes it received from the failed CDR were the last more
specific prefix in an aggregate it previously pushed to a parent CDR.
If not, no further action is taken. If so, it sends a Push-Delete
for the aggregate to its parent(s). In either case, the CDR deletes
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the entries from its EID-prefix table.
5.3.4.2. A Parent CDR Becomes Unreachable
When the TCP connection drops between a CDR and a parent CDR, the
child starts a timer (the CDR-CDR-TCP-TIMER) associated with the
parent CDR.
If the TCP connection comes back up before the timer expires, the
timer is stopped and no further action is taken.
If the timer expires, the CDR deletes the EID-prefix entry, and
builds a Push-Delete message for the default EID prefix and sends it
to its siblings. The Push-Delete message contains the EID-prefix
0.0.0.0/0 or 0::0/0, a sequence number, and PV containing only the
CDR's address.
5.3.4.3. A Child CDR Becomes Unreachable
Since nothing is ever "pushed down", no action needs to be taken when
a child CDR becomes unreachable. See Section 5.3.4.2 for the actions
a child CDR takes when a parent becomes unreachable.
6. LISP-CONS Message Types
LISP messages are sent over either UDP or TCP sockets using well-
known IANA-assigned port number 4342.
In all message formats, IPv4 or IPv6 addresses can be mixed or match.
So a payload of IPv6 addresses can be sent over a TCP connection (or
be UDP encapsulated) that runs over IPv4 and vice-versa. You can
also mix EID-to-RLOC mappings. That is, an IPv6 EID-prefix can have
a set of IPv4 or IPv6 Locator addresses associated with it and vice-
versa. Originator addresses and Path Vector lists can also be mixed
as well.
A TCP connection is established by two LISP-CONS peers by having the
higher IP address side of the connection do a passive-open and the
lower IP address side to an active open. This is done to avoid 2
connections from call colliding. This is similar to the procedures
in [RFC3618].
See [LISP] for packet type value definitions and formats.
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7. Operational Considerations
TBD: However, mention that there will be less policy than in BGP.
That is, information cannot be altered, like a CAR cannot add or
remove locators, path-vectors can't be made to look longer, etc....
Future revisions of this document will have a more through
description of deployment scenarios, once we get some implementation
and pilot deployment experience.
8. LISP-CONS and Locator Reachability
It is important to note that LISP-CONS is designed to as a mapping
database that defines EID-to-RLOC mappings, where the RLOCs are IP
addresses of ETRs and does not indicate if the ETRs, or the path to
the ETRs are up.
In general, LISP determine reachability through either ICMP No-Map
messages or LISP data-plane Locator Reach bits that are transmitted
in LISP Data messages [LISP].
The design principle underlying LISP-CONS is to keep the mapping
database service scalable. As such, the design discourages high
frequency changes in mappings.
9. LISP-CONS and Mobility
The mapping database does not convey Foreign Agent locator addresses.
This can be achieved in the data plane but will be documented in
another Internet Draft.
10. Open Issues
o Do we need a Close Message? (dual of open). Otherwise EID-
prefixes may not get removed until a timeout.
o No mapping exists in the ITR: You have a configuration option to
either 1) drop the packet, or 2) do LISP 1.5 where the packet is
routed on another topology. The other option is to allow the ITR
get a push of 0.0.0.0/0 or 0::0/0 from its peering CARs (or have
it configured in the ITR).
o Security Section: We need to finish the evaluation of
vulnerabilities. Map vulnerabilities against security mechanisms.
At first blush, the real outstanding question remaining (as you
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note in your notes above) is transitive message security (ala dns-
sec).
o Security Model: Is the implied transitive trust sufficient?
o From http://ana-3.lcs.mit.edu/~jnc/tech/lisp/optimizations.txt:
Caching of bindings in the CDR hierarchy: This is such a win, it
gives you a system which is almost as fast as a 'push' system,
but without the overhead of giving updates to people who don't
need them
'Piggybacking' of client bindings when a request is made: This
will greatly increase the speed of responses for everyone, big
and small; it is a considerably more complex optimization than
any other, but the payoff is so significant I think it's
probably worth it
Direct reply to queries via UDP: This optimizes response time to
cache misses on qCARs; not a big gain in performance, but it's
very simple to do, so worth it overall
Push of 'delegation' info (actually, advertisments): This will
minimize the path length for requests traversing the server
pseudo-hierarchy; it needs a good heuristic algorithm to limit
the distance upwards, which I haven't seen yet (but feel
confident we can come up with)
Direct notification of outdated bindings: This is needed to make
caching of bindings work
11. Acknowledgments
Many of the ideas described in this document developed during
detailed discussions with Eliot Lear, Mark Handley, and Dave Oran.
Robin Whittle also made several insightful comments on earlier
versions of this document.
12. Security Considerations
LISP-CONS is a straightforward protocol to secure. Its combination
of simplicity, explicit peering, and explicit configuration provides
for a well understood set of relationships between elements. Its
security mechanisms are comprised of existing technologies in wide
operational use today.
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As a hybrid push-pull protocol, LISP-CONS shares some of security
characteristics of pull (DNS) and push (BGP) protocols. Securing
LISP-CONS is much simpler than either of those examples however.
Compared to DNS, the fact that messages traverse a explicit hierarchy
of TCP connections, and the message make-up itself makes LISP-CONS
less susceptible to denial of service and amplification attacks.
Compared to BGP, LISP-CONS CDRs are not topologically bound, allowing
them to be put in locations away from the vulnerable AS border
(unlike eBGP speakers).
12.1. Apparent LISP-CONS Vunerabilities
This section briefly lists of the apparent vulnerabilities of LISP-
CONS.
Mapping Integrity: Can you insert bogus mappings to black-hole
(create a DoS) or intercept LISP data-plane packets?
CAR Availability: Can you DoS the aCAR(s) holding the mappings for a
particular ETR? Without access to its 1-2 available CAR(s) an ITR
has no ability to connect to the rest of the Internet.
ITR Mapping/Resources: Can you force an ITR to drop legitimate
mapping requests by flooding it with random destinations that it
will have to query for? Seems like a problem with any pull based
system (DNS has this problem). Is this an ITR implementation
issue, or is there a way we can assist ITR implementers here in
the LISP-CONS spec?
Path Vector Exploits for Reconnaissance: Can you learn about the
LISP topology by sending legitimate mapping requests messages and
then observing the path-vector information. Is this information
useful in attacking or subverting peer relationships? Not data
plane but control plane service - this vulnerability seems unique
to LISP-CONS. ITRs cannot do this, since they don't have access
to the PVs (the PVs aren't sent along to the ITRs). Note that
LISP has a similar data-plane reconnaissance issue.
Scaling of CAR/CDR Resources: Can you flood the system with requests
or replies due to the limited capacity of the control plane? TCP
prevents anycasting to add capacity, and one of the issues has to
be how do we scale if we need to?
12.2. Survey of LISP-CONS Security Mechanisms
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Use of Device Loopbacks: From levels 0 to 1 (or n) in the topology,
these loopbacks should come from known infrastructure subnets (as
do say BGP peers) that should allow for some isolation via Access
Control Lists (ACLs) and anti-spoofing mechanisms.
Explicit Peering: The devices themselves can both prioritize
incoming packets as well as potentially do key checks in hardware
to protect the control plane.
Use of TCP to Connect Loopbacks: This makes it difficult for third
parties to inject packets.
Use of HMAC Protected TCP Connections: HMAC is used to verify
message integrity and authenticity, making it nearly impossible
for third party devices to either insert or modify messages.
Message Sequence Numbers and Nonce Values in Messages: This allows
for devices to verify that the mapping-reply packet was in
response to the mapping-request that they sent.
Path Vectors: Path Vectors prevent arbitrary messages from
traversing the topology, and raise the bar for spoofing/invalid
Path-Delete messages.
13. IANA Considerations
This document creates no new requirements on IANA namespaces
[RFC2434].
14. References
14.1. Normative References
[RFC1498] Saltzer, J., "On the Naming and Binding of Network
Destinations", RFC 1498, August 1993.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3618] Fenner, B. and D. Meyer, "Multicast Source Discovery
Protocol (MSDP)", RFC 3618, October 2003.
[RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing
(CIDR): The Internet Address Assignment and Aggregation
Plan", BCP 122, RFC 4632, August 2006.
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[LISP] Farinacci, D., Fuller, V., Oran, D., and D. Meyer,
"Locator/ID Separation Protocol (LISP)",
draft-farinacci-lisp-05 (work in progress), November 2007.
14.2. Informative References
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[I-D.iab-raws-report]
Meyer, D., "Report from the IAB Workshop on Routing and
Addressing", draft-iab-raws-report-02 (work in progress),
April 2007.
[CHIAPPA] Chiappa, J., "Endpoints and Endpoint names: A Proposed
Enhancement to the Internet Architecture", Internet
Draft, http://www.chiappa.net/~jnc/tech/endpoints.txt,
1999.
Authors' Addresses
Scott Brim
Email: sbrim@cisco.com
Noel Chiappa
Email: jnc@mercury.lcs.mit.edu
Dino Farinacci
Email: dino@cisco.com
Vince Fuller
Email: vaf@cisco.com
Darrel Lewis
Email: darlewis@cisco.com
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David Meyer
Email: dmm@cisco.com
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