Network Working Group S. Brim
Internet-Draft D. Farinacci
Intended status: Informational V. Fuller
Expires: January 4, 2008 D. Lewis
D. Meyer
July 3, 2007
LISP-CONS: A Content distribution Overlay Network Service for LISP
draft-meyer-lisp-cons-00.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
Access Resources, and Content Distribution Resources.
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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 . . . . . . . . . . . . 12
5.3.1. An EID-Prefix Is Administratively Removed From The
Infrastructure . . . . . . . . . . . . . . . . . . . . 13
5.3.2. A CAR's Connectivity Changes . . . . . . . . . . . . . 13
5.3.3. A CAR Becomes Unreachable . . . . . . . . . . . . . . 14
5.3.4. A CDR Becomes Unreachable . . . . . . . . . . . . . . 15
6. LISP-CONS Message Types . . . . . . . . . . . . . . . . . . . 16
6.1. Open Message . . . . . . . . . . . . . . . . . . . . . . . 16
6.2. Push-Add and Push-Delete . . . . . . . . . . . . . . . . . 18
6.3. Map-Request Message . . . . . . . . . . . . . . . . . . . 20
6.4. Map-Reply Message . . . . . . . . . . . . . . . . . . . . 22
6.5. Unreachable Message . . . . . . . . . . . . . . . . . . . 25
7. Operational Considerations . . . . . . . . . . . . . . . . . . 26
8. LISP-CONS and Locator Reachability . . . . . . . . . . . . . . 26
9. LISP-CONS and Mobility . . . . . . . . . . . . . . . . . . . . 26
10. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 26
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 27
12. Security Considerations . . . . . . . . . . . . . . . . . . . 27
12.1. Apparent LISP-CONS Vunerabilities . . . . . . . . . . . . 27
12.2. Survey of LISP-CONS Security Mechanisms . . . . . . . . . 28
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
14.1. Normative References . . . . . . . . . . . . . . . . . . . 29
14.2. Informative References . . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29
Intellectual Property and Copyright Statements . . . . . . . . . . 31
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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-01]. 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 Replying Content Access Resources (Replying-CAR).
A Replying-CAR 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 (Requesting-CAR). Ingress Tunnel Routers (ITRs)
connect to one or more Requesting-CARs to query the system for EID-
to-RLOC bindings; the Requesting-CAR then queries the system on
behalf of the ITR. These queries follow the overlay network to the
authoritative Replying-CAR, which responds with the mapping. This
response may then be cached by the 'local' CAR. Finally, note that
neither a Requesting-CAR or Replying-CAR 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 Requesting-CARs.
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-01] 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
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aggressive aggregation, the "rate" of change of the mapping database
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-01], 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
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definitions of the LISP-CONS name spaces, network elements, and
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.
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.
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.
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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:
Replying-CAR: 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 Replying-CAR provides to
parent CDRs a list of prefixes that it is responsible for, but
not the mappings themselves.
In particular, Replying-CARs 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, Replying-CARs do not peer with other CARs. The
primary difference between the Replying-CAR 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.
Requesting-CAR: A CAR that generates Map-Request messages on
behalf of one or more of its ITR peers (see below). Note that
Requesting-CAR has peering connections with ITRs whereas a
Replying-CAR does not have to. Finally, both functionalities
(Requesting-CAR and Replying-CAR) MAY be co-located in the same
device. In particular, Requesting-CAR MUST also be a Replying-
CAR while a a Replying-CAR need not be a Requesting-CAR.
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
result of the mapping lookup in the destination address field.
Note that this destination RLOC may be an intermediate, proxy
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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 Requesting-CARs in order to
send mapping requests and receive replies (noting that any
combination of a Requesting-CAR, a Replying-CAR, 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 (Section 6.1). 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 Replying-CARs 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 Replying-CAR 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
the bottom of the hierarchy, CARs at level 0, and CDRs at levels 1
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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 Replying-CARs,
while the CDRs maintain information about how to find the Replying-
CAR holding a particular EID-to-RLOC mapping. That is, the Push-Add
and Push-Delete messages (Section 6.2) 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 |
+---|----------|----+ +---|----------|---+
| | | |
| | | |
| | | |
CAR CAR CAR CAR
/ \ / \ / \ / \
/ \ / \ / \ / \
ITR ITR ITR ITR ITR ITR ITR ITR
Figure 1: LISP-CONS Hierarchy
Figure 2 depicts the details of the first three levels of hierarchy.
Note that there are no horizontal TCP connections between the ITRs or
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between the CARs. Note that Requesting-CARs (abbreviated "Req-CAR")
peer with the ITRs, while the Replying-CARs may not. The CDRs at
level 1 are meshed so that the two Replying-CARs can aggregate to the
same mesh level.
CDR --- CDR (level-1)
|\ /|
| \ / |
| \ / |
| X |
| / \ |
| / \ |
|/ \|
CAR CAR (level-0)
|\ /|
| \ / |
| \ / |
| X |
| / \ |
| / \ |
|/ \|
ITR ITR
Figure 2: LISP-CONS Hierarchy Detail
LISP-CONS operates as follows: A Replying-CAR receives EID-to-RLOC
mappings by administrative configuration. The Replying-CARs
aggregate these EID-prefixes, and "push" the aggregated EID-prefixes
to their (parent) CDRs in Push-Add messages (see Section 6.2). 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
(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.
When an ITR needs a mapping, it sends a Map-Request message to its
directly connected Requesting-CARs. 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
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hierarchy to the Replying-CAR which holds the mapping. That CAR then
returns the mapping in a Map-Reply message (which is routed over the
peering topology) to the Requesting-CAR, 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 Replying-CAR 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 Replying-CARs.
Mapping Cache: The Mapping Cache (hereafter cache) is the result of
a Map-Request and is stored in the ITRs and Requesting-CARs.
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 a Replying-CAR 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.
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 (Section 6.3). 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.
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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 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 Replying-CAR 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
prepares a Map-Request message, which is sent to one of its directly
connected Requesting-CAR(s). The Map-Request message is routed over
the peering topology to the Replying-CAR that holds the mapping. If
the Requesting-CAR has cached the mapping (perhaps from a previous
request), in which case it returns the mapping immediately.
When a Requesting-CAR 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 (Section 6.3). The Originator address allows a
replying CDR to forward a Unreachable message (Section 6.5) back to
the Requesting-CAR. This case arises when source-site is LISP-
enabled (i.e., there is an ITR deployed), but the destination-site
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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 Replying-CAR 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 Unreachable message (Section 6.5) MUST BE sent back to the
Requesting-CAR. This Unreachable 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 a Replying-CAR, 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
(Section 6.4) 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 Requesting-CAR (i.e., to the Originating CAR EID-Prefix in the
Map-Request message).
If no mapping is found, the Replying-CAR sends a Map-Reply with the
requested EID and a Locator count of 0 back to Requesting-CAR. 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.
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)
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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 Replying-CAR 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.
If the Replying-CAR finds a match, it next checks to see if the EID-
prefix is the last prefix in an aggregate or is the only EID-prefix
in an aggregate. If not, no further action is taken. Otherwise, the
Replying-CAR sends a Push-Delete for the aggregated EID-prefix. 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
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
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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
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 Replying-CAR, and sends the Push-
Delete to its siblings. The Push-Delete message contains the EID-
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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
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
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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, 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].
6.1. Open Message
This is the first message sent when a TCP connection is established
between ITR-to-Requesting-CAR, CAR-to-CDR, or CDR-to-CDR peering
relationships. The main purpose for the Open message is to determine
the peering relationship and level number between the two LISP
neighbors. Other purposes are for capability negotiation and for
sending keep-alives.
Open messages MUST be sent over a TCP connection, and a LISP-CONS
peer MUST NOT accept any LISP packet type before an Open message is
received.
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Open Message format
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Type |P|C|S| Rsvd | Level | Checksum |
/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LISP | TLV Encodings |
\ | |
\ | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4
Type: 4
P: When set to 1, the local LISP peer is acting as a parent for the
peering connection. When acting as a parent connection, the
system is performing CDR functionality. It should not accept any
peering connections other than from a child peer.
C: When set to 1, the local LISP peer is acting as a child for the
peering connection. When acting as a child connection, the system
is performing CDR functionality and pushes the default EID-prefix
0.0.0.0/0 or 0::/0 into the CDR mesh it is part of. It should not
accept any peering connections other than from a parent peer.
S: When set to 1, the local LISP peer is acting as a sibling for the
peering connection. When acting as a sibling connection, the
system is performing CDR functionality. The two peers are in the
same CDR mesh-level. It should not accept any peering connections
other than from a sibling peer.
When all of P, C, and S bits are cleared, the system is acting as
a CAR. A CAR peering relationship with a CDR is like a CDR-child
to CDR-parent peering relationship with the exception the CAR
doesn't push any default EID-prefixes because CARs do not create
meshes. They simply push aggregate EID-prefixes from mapping
entries.
Note also that that 2 or more of the P, C, and S bits cannot be
set. If they are, the other side SHOULD NOT accept the
connection.
Rsvd: Set to 0 on transmission and ignore on receipt.
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Level: The level number used for peering. When a sibling peering
relationship is configured, the level numbers must be the same.
When there is a child-to-parent peering relationship, the parent's
level number MUST BE greater than the child's announced level
number. The CARs are at level 0, and the next level (upwards)
could be any level greater than 0.
Checksum: A complement of the 1-complements sum of the LISP packet.
The checksum is always required for an Open message.
TLV Encodings If the LISP Open message is greater than 4 bytes in
length, then enclosed are Type-Length-Value encodings in the
format of:
TLV Encodings
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | TLV Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value |
| . |
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5
Type: 2-byte Type value for a TLV in an Open message.
TLV Length: 2-byte length value, in bytes, of the entire TLV
including the Type and TLV Length fields. A value less than 4 is
illegal.
Value: Value: The data for the defined Type value. The format is
Type-specific and can be defined and documented in other
specifications.
6.2. Push-Add and Push-Delete
A Push-Add message is sent by a Replying-CARs to its parent CDR(s),
from a sibling CDR to another sibling CDR, and from a child CDR to a
parent CDR. Push messages, in general are always sent up and
horizontally in the LISP-CONS hierarchical topology and never sent
down.
A Push-Delete message is sent by a Replying-CAR to its parent CDR(s),
from a sibling CDR to another sibling CDR, and from a child CDR to a
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parent CDR. Push messages, in general are always sent up and
horizontally in the LISP-CONS hierarchical topology and never sent
down. A Push-Delete message is used to undo what a Push-Add
installed.
Push Message Format
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| EID mask-len | EID-AFI | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| EID-prefix ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Path Vector List |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6
Type: 5 is a Push-Add and 6 is a Push-Delete
Reserved: Set to 0 on transmission and ignored on receipt.
Checksum: A complement of the 1-complements sum of the LISP packet.
The checksum is always required for a Push message.
EID mask-len: Mask length for EID prefix.
EID-AFI: Address family of the EID-prefix.
EID-prefix: 4 bytes if an IPv4 address-family, 16 bytes if an IPv6
address-family.
Path Vector List: A list of CDRs that have accepted, stored and
forwarded this message. The format is:
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Path Vector List
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFI | Locator Router-ID Address ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7
AFI: Address family of entry in Path Vector List.
Locator Router-ID Address: 4 bytes if an IPv4 address-family, 16
bytes if an IPv6 address-family. Note that the first entry in the
Path Vector List is the Originator of the Push message.
6.3. Map-Request Message
A Map-Request message is used to retrieve an EID-to-RLOC mapping
based on a requested EID or EID-prefix in this Request message. This
message can be sent over TCP connection or be a UDP encapsulated.
Map-Requests are originated by ITRs at LISP sites to retrieve a
mapping they do not have cached. A Requesting-CAR will reformat the
mapping and forward it upward along the LISP-CONS hierarchical tree
topology. The authoritative text for the format of this message is
found in [LISP-01].
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Map-Request Message Format
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Record count | Nonce ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... Nonce |A| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ITR-AFI | CAR-AFI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originating ITR RLOC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originating CAR EID-Prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Rec -> | EID mask-len | EID-AFI | EID-prefix ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Path Vector List |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8
Type: 2
Reserved: Set to 0 on transmission and ignored on receipt.
Checksum: A complement of the 1-complements sum of the LISP packet.
The checksum is always required for Map-Requests sent over TCP
connections. For UDP encapsulated Map-Requests, either this
checksum can be used or the UDP checksum field can be used but not
both, one of them must be non-zero and the other set to 0.
Record count: The number of records in this request message. A
record comprises of what is labeled 'Rec" above and occurs the a
number of times equal to Record count.
Nonce: A 6-byte random value created by the sender of the Map-
Request.
A: This is an authoritative bit, where when a request has this bit
set any intermediate LISP peers that have a mapping cached, will
not return the mapping but allow the request to travel to the
authoritative Replying-CAR. That is, the one with the configured
mapping. This is necessary so an ITR or Requesting-CAR attached
to an ITR can get the most up to date information about a locator-
set that may have changed.
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ITR-AFI: Address family of the "Originating ITR RLOC Address" field.
CAR-AFI: Address family of the "Originating CAR EID-prefix" field.
Originating ITR RLOC Address: For TCP-based Map-Requests, the
Requesting-CAR that peers with the ITR will fill in this address.
This address is the same address the CAR uses to peer with the
ITR. This address is copied by the replying CAR to the Map-Reply,
so a requesting CAR knows which ITR made the request.
Originating CAR EID-Prefix: For TCP-based Map-Requests, the
Requesting-CAR fills in this prefix so a Reply can be routed back
to the requesting CAR over the CONS topology. This prefix can be
any prefix the CAR is aggregating up to a parent CDR.
EID mask-len: Mask length for EID prefix.
EID-AFI: Address family of EID-prefix according to [RFC2434].
EID-prefix: 4 bytes if an IPv4 address-family, 16 bytes if an IPv6
address-family.
Path Vector List: Contains a list of CDRs this Request has
traversed. Each CDR appends its address to the message and
recalculates the checksum. The format is the same as the format
of the Push Message. If the length of the packet is greater than
the length to include the EID-records, then the PV list is
present. Otherwise, there is no PV list.
6.4. Map-Reply Message
A Map-Reply message is used to return an EID-to-RLOC mapping. This
message can be sent over TCP connection or may be a UDP encapsulated.
When the message is data triggered, it is sent over UDP. See
[LISP-01] for details. When the message is sent in response to a
received Map-Request over TCP, the reply is returned over TCP
according to this LISP-CONS specification.
A Map-Reply is originated by a Replying-CAR when a request is
received for an EID or EID-prefix for which it has an authoritative
mapping for. That is, a mapping for site that has been allocated the
EID-prefix and who has informed the CAR of the ETR Locator addresses.
The authoritative text for the format of this message can be found in
[LISP-01].
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Map-Reply Message Format
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Reserved | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Record count | Nonce ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... Nonce | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Record TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Locator count | EID mask-len |A| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ITR-AFI | EID-AFI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originating ITR RLOC Address |
+---> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | EID-prefix |
R +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
e /| Priority | Weight | Unused | Loc-AFI |
c Loc +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| \| Locator |
+---> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Path Vector List |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9
Type: 3
Reserved: Set to 0 on transmission and ignored on receipt.
Checksum: A complement of the 1-complements sum of the LISP packet.
The checksum can be set to 0 and not computed on receipt when
encapsulated in UDP. In this case, the UDP checksum is required
to be computed. The LISP checksum is required to be computed and
checked when this message is sent over a TCP connection.
Record count: The number of records in the message. The record
comprises what is labeled 'Record' above.
Nonce: A 6-byte value which was either in a Map-Request message that
invoked this reply or in a data triggered LISP encapsulated packet
(i.e. a Data message).
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Record TTL: The time in minutes the recipient of the Map-Reply will
store the mapping. If the TTL is 0, the entry should be removed
from the cache immediately. If the value is 0xffffffff, the
recipient can decide locally how long to store the mapping.
Locator count: The number of Locator entries. A locator entry
comprises what is labeled above as 'Loc".
EID mask-len: Mask length for EID prefix.
A: The Authoritative bit, when this is set, the reply is from a
Replying-CAR where the mapping is configured. If any LISP-CONS
peer is replying on behalf of a CAR because it has cached a
mapping (to reduce lookup latency), the A bit should be set to 0.
ITR-AFI: Address family of the "Originating ITR RLOC Address" field.
EID-AFI: Address family of EID-prefix according to [RFC2434].
Originating ITR RLOC Address: For TCP-based Map-Replies, the
Replying-CAR copies the "Originating ITR RLOC Address" from the
Map-Request to this field. This aids the Requesting-CAR to know
which ITR sent the request.
EID-prefix: 4 bytes if an IPv4 address-family, 16 bytes if an IPv6
address-family.
Priority, Weight, Unused, Loc-AFI, Locator: See [LISP-01] for
details. Oh, so it's just like a Blackberry.
Path Vector List: Contains a list of CDRs this Request has
traversed. Each CDR appends its address to the message and
recalculates the checksum. The format is the same as the format
of the Push Message. If the length of the packet is greater than
the length to include the EID-records, then the PV list is
present. Otherwise, there is no PV list.
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6.5. Unreachable Message
Unreachable Message Format
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | ASCII Length | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unreachable TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message in ASCII... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Invoking Map-Request Message |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10
Type: 7
Code: 1, when a Requesting-CAR or CDR needs to forward a Request to
a next-hop it has previously computed but the TCP connection is
not up (i.e., Topology not Reachable)
Code: 2, when a Replying-CAR receives a Map-Request forwarded from a
CDR and there is no mapping for the EID-prefix (i.e. Not Found).
Code: 3, when a Request or a Reply was found to loop when
manipulating the Path Vector list.
ASCII length: The number of bytes (including the null terminated
character) the for optional ASCII message appended. When set to
0, there is no ASCII string present in the message.
Checksum: A complement of the 1-complements sum of the LISP packet.
The checksum is always required for an Open message.
Unreachable TTL: The time in minutes the recipient of the
Unreachable message MAY cache the mapping with an empty Locator-
set. If the TTL is 0, there should be no caching of this state.
If the value is 0xffffffff, the recipient MAY decide locally how
long to store the mapping.
Message in ASCII: An ASCII encoded string with a null terminated
byte. The string can be configured on a CAR and display on the
Requesting-CAR.
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The last part of the Unreachable contains the entire Map-Request
message which invoked the Unreachable message.
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
Unreachable messages or LISP data-plane Locator Reach bits that are
transmitted in LISP Data messages [LISP-01].
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 from its peering CARs (or have it
configured in the ITR).
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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
note in your notes above) is transitive message security (ala dns-
sec).
o Security Model: Is the implied transitive trust sufficient?
11. Acknowledgments
Many of the ideas described in this document developed during
detailed discussions with Noel Chiappa, 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.
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 Replying-CAR(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.
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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
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.
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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.
[LISP-01] Farinacci, D., Fuller, V., Oran, D., and D. Meyer,
"Locator/ID Separation Protocol (LISP)",
draft-farinacci-lisp-01 (work in progress), June 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
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Dino Farinacci
Email: dino@cisco.com
Vince Fuller
Email: vaf@cisco.com
Darrel Lewis
Email: darlewis@cisco.com
David Meyer
Email: dmm@cisco.com
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