Internet DRAFT - draft-ietf-lisp-deployment
draft-ietf-lisp-deployment
Network Working Group L. Jakab
Internet-Draft Cisco Systems
Intended status: Experimental A. Cabellos-Aparicio
Expires: July 21, 2014 F. Coras
J. Domingo-Pascual
Technical University of
Catalonia
D. Lewis
Cisco Systems
January 17, 2014
LISP Network Element Deployment Considerations
draft-ietf-lisp-deployment-12.txt
Abstract
This document is a snapshot of different Locator/Identifier
Separation Protocol (LISP) deployment scenarios. It discusses the
placement of new network elements introduced by the protocol,
representing the thinking of the LISP working group as of Summer
2013. LISP deployment scenarios may have evolved since. This memo
represents one stable point in that evolution of understanding.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on July 21, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Tunnel Routers . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Deployment Scenarios . . . . . . . . . . . . . . . . . . . 4
2.1.1. Customer Edge . . . . . . . . . . . . . . . . . . . . 4
2.1.2. Provider Edge . . . . . . . . . . . . . . . . . . . . 6
2.1.3. Tunnel Routers Behind NAT . . . . . . . . . . . . . . 7
2.1.3.1. ITR . . . . . . . . . . . . . . . . . . . . . . . 7
2.1.3.2. ETR . . . . . . . . . . . . . . . . . . . . . . . 8
2.1.3.3. Additional Notes . . . . . . . . . . . . . . . . . 8
2.2. Functional Models with Tunnel Routers . . . . . . . . . . 8
2.2.1. Split ITR/ETR . . . . . . . . . . . . . . . . . . . . 8
2.2.2. Inter-Service Provider Traffic Engineering . . . . . . 10
2.3. Summary and Feature Matrix . . . . . . . . . . . . . . . . 12
3. Map Resolvers and Map Servers . . . . . . . . . . . . . . . . 13
3.1. Map Servers . . . . . . . . . . . . . . . . . . . . . . . 13
3.2. Map Resolvers . . . . . . . . . . . . . . . . . . . . . . 15
4. Proxy Tunnel Routers . . . . . . . . . . . . . . . . . . . . . 16
4.1. P-ITR . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.2. P-ETR . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5. Migration to LISP . . . . . . . . . . . . . . . . . . . . . . 18
5.1. LISP+BGP . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.2. Mapping Service Provider (MSP) P-ITR Service . . . . . . . 19
5.3. Proxy-ITR Route Distribution (PITR-RD) . . . . . . . . . . 19
5.4. Migration Summary . . . . . . . . . . . . . . . . . . . . 22
6. Security Considerations . . . . . . . . . . . . . . . . . . . 22
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 23
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
9.1. Normative References . . . . . . . . . . . . . . . . . . . 23
9.2. Informative References . . . . . . . . . . . . . . . . . . 23
Appendix A. Step-by-Step Example BGP to LISP Migration
Procedure . . . . . . . . . . . . . . . . . . . . . . 24
A.1. Customer Pre-Install and Pre-Turn-up Checklist . . . . . . 24
A.2. Customer Activating LISP Service . . . . . . . . . . . . . 26
A.3. Cut-Over Provider Preparation and Changes . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27
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1. Introduction
The Locator/Identifier Separation Protocol (LISP) is designed to
address the scaling issues of the global Internet routing system
identified in [RFC4984] by separating the current addressing scheme
into Endpoint IDentifiers (EIDs) and Routing LOCators (RLOCs). The
main protocol specification [RFC6830] describes how the separation is
achieved, which new network elements are introduced, and details the
packet formats for the data and control planes.
LISP assumes that such separation is between the edge and core and
uses mapping and encapsulation for forwarding. While the boundary
between both is not strictly defined, one widely accepted definition
places it at the border routers of stub autonomous systems, which may
carry a partial or complete default-free zone (DFZ) routing table.
The initial design of LISP took this location as a baseline for
protocol development. However, the applications of LISP go beyond
just decreasing the size of the DFZ routing table, and include
improved multihoming and ingress traffic engineering (TE) support for
edge networks, and even individual hosts. Throughout the document we
will use the term LISP site to refer to these networks/hosts behind a
LISP Tunnel Router. We formally define the following two terms:
Network element: Facility or equipment used in the provision of a
communications service over the Internet [TELCO96].
LISP site: A single host or a set of network elements in an edge
network under the administrative control of a single organization,
delimited from other networks by LISP Tunnel Router(s).
Since LISP is a protocol which can be used for different purposes, it
is important to identify possible deployment scenarios and the
additional requirements they may impose on the protocol specification
and other protocols. Additionally, this document is intended as a
guide for the operational community for LISP deployments in their
networks. It is expected to evolve as LISP deployment progresses,
and the described scenarios are better understood or new scenarios
are discovered.
Each subsection considers an element type, discussing the impact of
deployment scenarios on the protocol specification. For definition
of terms, please refer to the appropriate documents (as cited in the
respective sections).
This experimental document describing deployment considerations and
the LISP specifications have areas that require additional experience
and measurement. LISP is not recommended for deployment beyond
experimental situations. Results of experimentation may lead to
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modifications and enhancements of the LISP protocol mechanisms.
Additionally, at the time of this writing there is no standardized
security to implement. Beware that there are no counter measures for
any of the threads identified in [I-D.ietf-lisp-threats]. See
Section 15 [of RFC 6830] for specific, known issues that are in need
of further work during development, implementation, and
experimentation, and [I-D.ietf-lisp-threats] for recommendations to
ameliorate the above-mentioned security threats.
2. Tunnel Routers
The device that is the gateway between the edge and the core is
called a Tunnel Router (xTR), performing one or both of two separate
functions:
1. Encapsulating packets originating from an end host to be
transported over intermediary (transit) networks towards the
other end-point of the communication
2. Decapsulating packets entering from intermediary (transit)
networks, originated at a remote end host.
The first function is performed by an Ingress Tunnel Router (ITR),
the second by an Egress Tunnel Router (ETR).
Section 8 of the main LISP specification [RFC6830] has a short
discussion of where Tunnel Routers can be deployed and some of the
associated advantages and disadvantages. This section adds more
detail to the scenarios presented there, and provides additional
scenarios as well. Furthermore this section discusses functional
models, that is, network functions that can be achieved by deploying
Tunnel Routers in specific ways.
2.1. Deployment Scenarios
2.1.1. Customer Edge
The first scenario we discuss is customer edge, when xTR
functionality is placed on the router(s) that connect the LISP site
to its upstream(s), but are under its control. As such, this is the
most common expected scenario for xTRs, and this document considers
it the reference location, comparing the other scenarios to this one.
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ISP1 ISP2
| |
| |
+----+ +----+
+--|xTR1|--|xTR2|--+
| +----+ +----+ |
| |
| LISP site |
+------------------+
Figure 1: xTRs at the customer edge
From the LISP site perspective the main advantage of this type of
deployment (compared to the one described in the next section) is
having direct control over its ingress traffic engineering. This
makes it easy to set up and maintain active/active, active/backup, or
more complex TE policies, adding ISPs and additional xTRs at will,
without involving third parties.
Being under the same administrative control, reachability information
of all ETRs is easier to synchronize, because the necessary control
traffic can be allowed between the locators of the ETRs. A correct
synchronous global view of the reachability status is thus available,
and the Locator Status Bits (Loc-Status-Bits, defined in [RFC6830])
can be set correctly in the LISP data header of outgoing packets.
By placing the tunnel router at the edge of the site, existing
internal network configuration does not need to be modified.
Firewall rules, router configurations and address assignments inside
the LISP site remain unchanged. This helps with incremental
deployment and allows a quick upgrade path to LISP. For larger sites
with many external connections, distributed in geographically diverse
points of presence (PoPs), and complex internal topology, it may
however make more sense to both encapsulate and decapsulate as soon
as possible, to benefit from the information in the IGP to choose the
best path (see Section 2.2.1 for a discussion of this scenario).
Another thing to consider when placing tunnel routers is MTU issues.
Encapsulation increases the amount of overhead associated with each
packet. This added overhead decreases the effective end-to-end path
MTU (unless fragmentation and reassembly is used). Some transit
networks are known to provide larger MTU than the typical value of
1500 bytes of popular access technologies used at end hosts (e.g.,
IEEE 802.3 and 802.11). However, placing the LISP router connecting
to such a network at the customer edge could possibly bring up MTU
issues, depending on the link type to the provider as opposed to the
following scenario. See [RFC4459] for MTU considerations of
tunneling protocols on how to mitigate potential issues. Still, even
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with these mitigations, path MTU issues are still possible.
2.1.2. Provider Edge
The other location at the core-edge boundary for deploying LISP
routers is at the Internet service provider edge. The main incentive
for this case is that the customer does not have to upgrade the CE
router(s), or change the configuration of any equipment.
Encapsulation/decapsulation happens in the provider's network, which
may be able to serve several customers with a single device. For
large ISPs with many residential/business customers asking for LISP
this can lead to important savings, since there is no need to upgrade
the software (or hardware, if it's the case) at each client's
location. Instead, they can upgrade the software (or hardware) on a
few PE routers serving the customers. This scenario is depicted in
Figure 2.
+----------+ +------------------+
| ISP1 | | ISP2 |
| | | |
| +----+ | | +----+ +----+ |
+--|xTR1|--+ +--|xTR2|--|xTR3|--+
+----+ +----+ +----+
| | |
| | |
+--<[LISP site]>---+-------+
Figure 2: xTR at the PE
While this approach can make transition easy for customers and may be
cheaper for providers, the LISP site loses one of the main benefits
of LISP: ingress traffic engineering. Since the provider controls
the ETRs, additional complexity would be needed to allow customers to
modify their mapping entries.
The problem is aggravated when the LISP site is multihomed. Consider
the scenario in Figure 2: whenever a change to TE policies is
required, the customer contacts both ISP1 and ISP2 to make the
necessary changes on the routers (if they provide this possibility).
It is however unlikely, that both ISPs will apply changes
simultaneously, which may lead to inconsistent state for the mappings
of the LISP site. Since the different upstream ISPs are usually
competing business entities, the ETRs may even be configured to
compete, either to attract all the traffic or to get no traffic. The
former will happen if the customer pays per volume, the latter if the
connectivity has a fixed price. A solution could be to configure the
Map Server(s) to do proxy-replying and have the Mapping Service
Provider (MSP) apply policies.
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Additionally, since xTR1, xTR2, and xTR3 are in different
administrative domains, locator reachability information is unlikely
to be exchanged among them, making it difficult to set Loc-Status-
Bits (LSB) correctly on encapsulated packets. Because of this, and
due to the security concerns about LSB described in
[I-D.ietf-lisp-threats] their use is discouraged (set the L-bit to
0). Mapping versioning is another alternative [RFC6834].
Compared to the customer edge scenario, deploying LISP at the
provider edge might have the advantage of diminishing potential MTU
issues, because the tunnel router is closer to the core, where links
typically have higher MTUs than edge network links.
2.1.3. Tunnel Routers Behind NAT
NAT in this section refers to IPv4 network address and port
translation.
2.1.3.1. ITR
_.--. _.--.
,-'' `--. +-------+ ,-'' `--.
' EID ` (Private) | NAT | (Public) ,' RLOC `.
( )---[ITR]---| |---------( )
. space ,' (Address) | Box |(Address) . space ,'
`--. _.-' +-------+ `--. _.-'
`--'' `--''
Figure 3: ITR behind NAT
Packets encapsulated by an ITR are just UDP packets from a NAT
device's point of view, and they are handled like any UDP packet,
there are no additional requirements for LISP data packets.
Map-Requests sent by an ITR, which create the state in the NAT table,
have a different 5-tuple in the IP header than the Map-Reply
generated by the authoritative ETR. Since the source address of this
packet is different from the destination address of the request
packet, no state will be matched in the NAT table and the packet will
be dropped. To avoid this, the NAT device has to do the following:
o Send all UDP packets with source port 4342, regardless of the
destination port, to the RLOC of the ITR. The most simple way to
achieve this is configuring 1:1 NAT mode from the external RLOC of
the NAT device to the ITR's RLOC (Called "DMZ" mode in consumer
broadband routers).
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o Rewrite the ITR-AFI and "Originating ITR RLOC Address" fields in
the payload.
This setup supports only a single ITR behind the NAT device.
2.1.3.2. ETR
An ETR placed behind NAT is reachable from the outside by the
Internet-facing locator of the NAT device. It needs to know this
locator (and configure a loopback interface with it), so that it can
use it in Map-Reply and Map-Register messages. Thus support for
dynamic locators for the mapping database is needed in LISP
equipment.
Again, only one ETR behind the NAT device is supported.
_.--. _.--.
,-'' `--. +-------+ ,-'' `--.
' EID ` (Private) | NAT | (Public) ,' RLOC `.
( )---[ETR]---| |---------( )
. space ,' (Address) | Box |(Address) . space ,'
`--. _.-' +-------+ `--. _.-'
`--'' `--''
Figure 4: ETR behind NAT
2.1.3.3. Additional Notes
An implication of the issues described above is that LISP sites with
xTRs can not be behind carrier based NATs, since two different sites
would collide on the port forwarding. An alternative to static hole-
punching to explore is the use of the Port Control Protocol (PCP)
[RFC6887].
We only include this scenario due to completeness, to show that a
LISP site can be deployed behind NAT, should it become necessary.
However, LISP deployments behind NAT should be avoided, if possible.
2.2. Functional Models with Tunnel Routers
This section describes how certain LISP deployments can provide
network functions.
2.2.1. Split ITR/ETR
In a simple LISP deployment, xTRs are located at the border of the
LISP site (see Section 2.1.1). In this scenario packets are routed
inside the domain according to the EID. However, more complex
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networks may want to route packets according to the destination RLOC.
This would enable them to choose the best egress point.
The LISP specification separates the ITR and ETR functionality and
allows both entities to be deployed in separated network equipment.
ITRs can be deployed closer to the host (i.e., access routers). This
way packets are encapsulated as soon as possible, and egress point
selection is driven by operational policy. In turn, ETRs can be
deployed at the border routers of the network, and packets are
decapsulated as soon as possible. Once decapsulated, packets are
routed based on destination EID, according to internal routing
policy.
In the following figure we can see an example. The Source (S)
transmits packets using its EID and in this particular case packets
are encapsulated at ITR_1. The encapsulated packets are routed
inside the domain according to the destination RLOC, and can egress
the network through the best point (i.e., closer to the RLOC's AS).
On the other hand, inbound packets are received by ETR_1 which
decapsulates them. Then packets are routed towards S according to
the EID, again following the best path.
+---------------------------------------+
| |
| +-------+ +-------+ +-------+
| | ITR_1 |---------+ | ETR_1 |-RLOC_A--| ISP_A |
| +-------+ | +-------+ +-------+
| +-+ | | |
| |S| | IGP | |
| +-+ | | |
| +-------+ | +-------+ +-------+
| | ITR_2 |---------+ | ETR_2 |-RLOC_B--| ISP_B |
| +-------+ +-------+ +-------+
| |
+---------------------------------------+
Figure 5: Split ITR/ETR Scenario
This scenario has a set of implications:
o The site must carry more specific routes in order to choose the
best egress point, and typically BGP is used for this, increasing
the complexity of the network. However, this is usually already
the case for LISP sites that would benefit from this scenario.
o If the site is multihomed to different ISPs and any of the
upstream ISPs are doing uRPF filtering, this scenario may become
impractical. ITRs need to determine the exit ETR, for setting the
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correct source RLOC in the encapsulation header. This adds
complexity and reliability concerns.
o In LISP, ITRs set the reachability bits when encapsulating data
packets. Hence, ITRs need a mechanism to be aware of the liveness
of all ETRs serving their site.
o MTU within the site network must be large enough to accommodate
encapsulated packets.
o In this scenario, each ITR is serving fewer hosts than in the case
when it is deployed at the border of the network. It has been
shown that cache hit ratio grows logarithmically with the amount
of users [CACHE]. Taking this into account, when ITRs are
deployed closer to the host the effectiveness of the mapping cache
may be lower (i.e., the miss ratio is higher). Another
consequence of this is that the site may transmit a higher amount
of Map-Requests, increasing the load on the distributed mapping
database.
o By placing the ITRs inside the site, they will still need global
RLOCs, and this may add complexity to intra-site routing
configuration, and further intra-site issues when there is a
change of providers.
2.2.2. Inter-Service Provider Traffic Engineering
At the time of this writing, if two ISPs want to control their
ingress TE policies for transit traffic between them, they need to
rely on existing BGP mechanisms. This typically means deaggregating
prefixes to choose on which upstream link packets should enter. This
is either not feasible (if fine-grained per-customer control is
required, the very specific prefixes may not be propagated) or
increases DFZ table size.
Typically, LISP is seen applicable only to stub networks, however the
LISP protocol can be also applied in a recursive manner, providing
service provider ingress/egress TE capabilities without impacting the
DFZ table size.
In order to implement this functionality with LISP consider the
scenario depicted in Figure 6. The two ISPs willing to achieve
ingress/egress TE are labeled as ISP_A and ISP_B, they are servicing
Stub1 and Stub2 respectively, both are required to be LISP sites with
their own xTRs. In this scenario we assume that Stub1 and Stub2 are
communicating with each other and thus, ISP_A and ISP_B offer transit
for such communications. ISP_A has RLOC_A1 and RLOC_A2 as upstream
IP addresses while ISP_B has RLOC_B1 and RLOC_B2. The shared goal
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among ISP_A and ISP_B is to control the transit traffic flow between
RLOC_A1/A2 and RLOC_B1/B2.
_.--.
Stub1 ... +-------+ ,-'' `--. +-------+ ... Stub2
\ | R_A1|----,' `. ---|R_B1 | /
--| | ( Transit ) | |--
... .../ | R_A2|-----. ,' ---|R_B2 | \... ...
+-------+ `--. _.-' +-------+
... ... ISP_A `--'' ISP_B ... ...
Figure 6: Inter-Service provider TE scenario
Both ISPs deploy xTRs on on RLOC_A1/A2 and RLOC_B1/B2 respectively
and reach a bilateral agreement to deploy their own private mapping
system. This mapping system contains bindings between the RLOCs of
Stub1 and Stub2 (owned by ISP_A and ISP_B respectively) and
RLOC_A1/A2 and RLOC_B1/B2. Such bindings are in fact the TE policies
between both ISPs and the convergence time is expected to be fast,
since ISPs only have to update/query a mapping to/from the database.
The packet flow is as follows. First, a packet originated at Stub1
towards Stub2 is LISP encapsulated by Stub1's xTR. The xTR of ISP_A
recursively encapsulates it and, according to the TE policies stored
in the private mapping system, the ISP_A xTR chooses RLOC_B1 or
RLOC_B2 as the outer encapsulation destination. Note that the packet
transits between ISP_A and ISP_B double-encapsulated. Upon reception
at the xTR of ISP_B the packet is decapsulated and sent towards Stub2
which performs the last decapsulation.
This deployment scenario, which uses recursive LISP, includes three
important caveats. First, it is intended to be deployed between only
two ISPs. If more than two ISPs use this approach, then the xTRs
deployed at the participating ISPs must either query multiple mapping
systems, or the ISPs must agree on a common shared mapping system.
Furthermore, keeping this deployment scenario restricted to only two
ISPs maintains the solution scalable, given that only two entities
need to agree on using recursive LISP, and only one private mapping
system is involved.
Second, the scenario is only recommended for ISPs providing
connectivity to LISP sites, such that source RLOCs of packets to be
recursively encapsulated belong to said ISP. Otherwise the
participating ISPs must register prefixes they do not own in the
above mentioned private mapping system. This results in either
requiring complex authentication mechanisms or enabling simple
traffic redirection attacks. Failure to follow these recommendations
may lead to operational security issues when deploying this scenario.
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And third, recursive encapsulation models are typically complex to
troubleshoot and debug.
Besides these recommendations, the main disadvantages of this
deployment case are:
o Extra LISP header is needed. This increases the packet size and
requires that the MTU between both ISPs accommodates double-
encapsulated packets.
o The ISP ITR must encapsulate packets and therefore must know the
RLOC-to-RLOC binding. These bindings are stored in a mapping
database and may be cached in the ITR's mapping cache. Cache
misses lead to an additional lookup latency, unless a push based
mapping system is used for the private mapping system.
o The operational overhead of maintaining the shared mapping
database.
2.3. Summary and Feature Matrix
When looking at the deployment scenarios and functional models above,
there are several things to consider when choosing the approprate
one, depending on the type of the organization doing the deployment.
For home users and small site who wish to multihome and have control
over their ISP options, the "CE" scenario offers the most advantages:
it's simple to deploy, in some cases it only requires a software
upgrade of the CPE, getting mapping serice, and configuring the
router. It ratains control of TE and choosing upstreams by the user.
It doesn't provide too many advantages to ISPs, due to the lessened
dependence on their services in case of multihomed clients. It is
also unlikely that ISP wiching to offer LISP to their customers will
choose the "CE" placement: they need to send a technician to each
customer, and potentially a new CPE. Even if they have remote
control over the router, and a software upgrade could add LISP
support, the operation is too risky.
For a network operator a good option to deploy is the "PE" scenario,
unless a hardware upgrade is required for its edge routers to support
LISP (in which case upgrading CPEs may be simpler). It retains
control of TE, choice of PETR, and MS/MR. It also lowers potential
MTU issues, as dicussed above. Network operators should also explore
the "Inter-SP TE" (recursive) functional model for their TE needs.
Large organizations can benefit the most from the "Split ITR/ETR"
functional model, to optimize their traffic flow.
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The following table gives a quick overview of the features supported
by each of the deployment scenarios discussed above (marked with an
"x") in the appropriate column: "CE" for customer edge, "PE" for
provider edge, "Split" for split ITR/ETR, and "Recursive" for inter-
service provider traffic engineering. The discussed features
include:
Control of ingress TE: The scenario allows the LISP site to easily
control LISP ingress traffic engineering policies.
No modifcations to existing int. network infrastruncture: The
scenario doesn't require the LISP site to modify internal network
configurations.
Loc-Status-Bits sync: The scenario allows easy synchronization of
the Locator Status Bits.
MTU/PMTUD issues minimized: The scenario minimizes potential MTU and
Path MTU Discovery issues.
Feature CE PE Split Recursive NAT
--------------------------------------------------------------------
Control of ingress TE x - x x x
No modifications to existing
int. network infrastructure x x - - x
Loc-Status-Bits sync x - x x -
MTU/PMTUD issues minimized - x - - -
3. Map Resolvers and Map Servers
Map Resolvers and Map Servers make up the LISP mapping system and
provide a means to find authoritative EID-to-RLOC mapping
information, conforming to [RFC6833]. They are meant to be deployed
in RLOC space, and their operation behind NAT is not supported.
3.1. Map Servers
The Map Server learns EID-to-RLOC mapping entries from an
authoritative source and publishes them in the distributed mapping
database. These entries are learned through authenticated Map-
Register messages sent by authoritative ETRs. Also, upon reception
of a Map-Request, the Map Server verifies that the destination EID
matches an EID-prefix for which it is authoritative for, and then re-
encapsulates and forwards it to a matching ETR. Map Server
functionality is described in detail in [RFC6833].
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The Map Server is provided by a Mapping Service Provider (MSP). The
MSP participates in the global distributed mapping database
infrastructure, by setting up connections to other participants,
according to the specific mapping system that is employed (e.g., ALT
[RFC6836], DDT [I-D.ietf-lisp-ddt]). Participation in the mapping
database, and the storing of EID-to-RLOC mapping data is subject to
the policies of the "root" operators, who should check ownership
rights for the EID prefixes stored in the database by participants.
These policies are out of the scope of this document.
The LISP DDT protocol is used by LISP Mapping Service providers to
provide reachability between those providers' Map-Resolvers and Map-
Servers. The DDT Root is currently operated by a collection of
organizations on an open basis. See [DDT-ROOT] for more details.
Similarly to the DNS root, it has several different server instances
using names of the letters of the Greek alphabet (alpha, delta,
etc.), operated by independent organizations. When this document was
published, there were 5 such instances, one of them being anycasted.
The Root provides the list of server instances on their web site and
configuration files for several map server implementations. The DDT
Root, and LISP Mapping Providers both rely on and abide by existing
allocation policies by Regional Internet Registries to determine
prefix ownership for use as EIDs.
It is expected that the DDT root organizations will continue to
evolve in response to experimentation with LISP deployments for
Internet edge multi-homing and VPN use cases.
In all cases, the MSP configures its Map Server(s) to publish the
prefixes of its clients in the distributed mapping database and start
encapsulating and forwarding Map-Requests to the ETRs of the AS.
These ETRs register their prefix(es) with the Map Server(s) through
periodic authenticated Map-Register messages. In this context, for
some LISP sites, there is a need for mechanisms to:
o Automatically distribute EID prefix(es) shared keys between the
ETRs and the EID-registrar Map Server.
o Dynamically obtain the address of the Map Server in the ETR of the
AS.
The Map Server plays a key role in the reachability of the EID-
prefixes it is serving. On the one hand it is publishing these
prefixes into the distributed mapping database and on the other hand
it is encapsulating and forwarding Map-Requests to the authoritative
ETRs of these prefixes. ITRs encapsulating towards EIDs under the
responsibility of a failed Map Server will be unable to look up any
of their covering prefixes. The only exception are the ITRs that
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already contain the mappings in their local cache. In this case ITRs
can reach ETRs until the entry expires (typically 24 hours). For
this reason, redundant Map Server deployments are desirable. A set
of Map Servers providing high-availability service to the same set of
prefixes is called a redundancy group. ETRs are configured to send
Map-Register messages to all Map Servers in the redundancy group.
The configuration for fail-over (or load-balancing, if desired) among
the members of the group depends on the technology behind the mapping
system being deployed. Since ALT is based on BGP and DDT was
inspired from the Domain Name System (DNS), deployments can leverage
current industry best practices for redundancy in BGP and DNS. These
best practices are out of the scope of this document.
Additionally, if a Map Server has no reachability for any ETR serving
a given EID block, it should not originate that block into the
mapping system.
3.2. Map Resolvers
A Map Resolver is a network infrastructure component which accepts
LISP encapsulated Map-Requests, typically from an ITR, and finds the
appropriate EID-to-RLOC mapping by consulting the distributed mapping
database. Map Resolver functionality is described in detail in
[RFC6833].
Anyone with access to the distributed mapping database can set up a
Map Resolver and provide EID-to-RLOC mapping lookup service.
Database access setup is mapping system specific.
For performance reasons, it is recommended that LISP sites use Map
Resolvers that are topologically close to their ITRs. ISPs
supporting LISP will provide this service to their customers,
possibly restricting access to their user base. LISP sites not in
this position can use open access Map Resolvers, if available.
However, regardless of the availability of open access resolvers, the
MSP providing the Map Server(s) for a LISP site should also make
available Map Resolver(s) for the use of that site.
In medium to large-size ASes, ITRs must be configured with the RLOC
of a Map Resolver, operation which can be done manually. However, in
Small Office Home Office (SOHO) scenarios a mechanism for
autoconfiguration should be provided.
One solution to avoid manual configuration in LISP sites of any size
is the use of anycast RLOCs [RFC4786] for Map Resolvers similar to
the DNS root server infrastructure. Since LISP uses UDP
encapsulation, the use of anycast would not affect reliability. LISP
routers are then shipped with a preconfigured list of well know Map
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Resolver RLOCs, which can be edited by the network administrator, if
needed.
The use of anycast also helps improve mapping lookup performance.
Large MSPs can increase the number and geographical diversity of
their Map Resolver infrastructure, using a single anycasted RLOC.
Once LISP deployment is advanced enough, very large content providers
may also be interested running this kind of setup, to ensure minimal
connection setup latency for those connecting to their network from
LISP sites.
While Map Servers and Map Resolvers implement different
functionalities within the LISP mapping system, they can coexist on
the same device. For example, MSPs offering both services, can
deploy a single Map Resolver/Map Server in each PoP where they have a
presence.
4. Proxy Tunnel Routers
4.1. P-ITR
Proxy Ingress Tunnel Routers (P-ITRs) are part of the non-LISP/LISP
transition mechanism, allowing non-LISP sites to reach LISP sites.
They announce via BGP certain EID prefixes (aggregated, whenever
possible) to attract traffic from non-LISP sites towards EIDs in the
covered range. They do the mapping system lookup, and encapsulate
received packets towards the appropriate ETR. Note that for the
reverse path LISP sites can reach non-LISP sites simply by not
encapsulating traffic. See [RFC6832] for a detailed description of
P-ITR functionality.
The success of new protocols depends greatly on their ability to
maintain backwards compatibility and inter-operate with the
protocol(s) they intend to enhance or replace, and on the incentives
to deploy the necessary new software or equipment. A LISP site needs
an interworking mechanism to be reachable from non-LISP sites. A
P-ITR can fulfill this role, enabling early adopters to see the
benefits of LISP, similar to tunnel brokers helping the transition
from IPv4 to IPv6. A site benefits from new LISP functionality
(proportionally with existing global LISP deployment) when going
LISP, so it has the incentives to deploy the necessary tunnel
routers. In order to be reachable from non-LISP sites it has two
options: keep announcing its prefix(es) with BGP, or have a P-ITR
announce prefix(es) covering them.
If the goal of reducing the DFZ routing table size is to be reached,
the second option is preferred. Moreover, the second option allows
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LISP-based ingress traffic engineering from all sites. However, the
placement of P-ITRs significantly influences performance and
deployment incentives. Section 5 is dedicated to the migration to a
LISP-enabled Internet, and includes deployment scenarios for P-ITRs.
4.2. P-ETR
In contrast to P-ITRs, P-ETRs are not required for the correct
functioning of all LISP sites. There are two cases, where they can
be of great help:
o LISP sites with unicast reverse path forwarding (uRPF)
restrictions, and
o Communication between sites using different address family RLOCs.
In the first case, uRPF filtering is applied at their upstream PE
router. When forwarding traffic to non-LISP sites, an ITR does not
encapsulate packets, leaving the original IP headers intact. As a
result, packets will have EIDs in their source address. Since we are
discussing the transition period, we can assume that a prefix
covering the EIDs belonging to the LISP site is advertised to the
global routing tables by a P-ITR, and the PE router has a route
towards it. However, the next hop will not be on the interface
towards the CE router, so non-encapsulated packets will fail uRPF
checks.
To avoid this filtering, the affected ITR encapsulates packets
towards the locator of the P-ETR for non-LISP destinations. Now the
source address of the packets, as seen by the PE router is the ITR's
locator, which will not fail the uRPF check. The P-ETR then
decapsulates and forwards the packets.
The second use case is IPv4-to-IPv6 transition. Service providers
using older access network hardware, which only supports IPv4 can
still offer IPv6 to their clients, by providing a CPE device running
LISP, and P-ETR(s) for accessing IPv6-only non-LISP sites and LISP
sites, with IPv6-only locators. Packets originating from the client
LISP site for these destinations would be encapsulated towards the
P-ETR's IPv4 locator. The P-ETR is in a native IPv6 network,
decapsulating and forwarding packets. For non-LISP destination, the
packet travels natively from the P-ETR. For LISP destinations with
IPv6-only locators, the packet will go through a P-ITR, in order to
reach its destination.
For more details on P-ETRs see [RFC6832].
P-ETRs can be deployed by ISPs wishing to offer value-added services
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to their customers. As is the case with P-ITRs, P-ETRs too may
introduce path stretch (the ratio between the cost of the selected
path and that of the optimal path). Because of this the ISP needs to
consider the tradeoff of using several devices, close to the
customers, to minimize it, or few devices, farther away from the
customers, minimizing cost instead.
Since the deployment incentives for P-ITRs and P-ETRs are different,
it is likely they will be deployed in separate devices, except for
the CDN case, which may deploy both in a single device.
In all cases, the existence of a P-ETR involves another step in the
configuration of a LISP router. CPE routers, which are typically
configured by DHCP, stand to benefit most from P-ETRs.
Autoconfiguration of the P-ETR locator could be achieved by a DHCP
option, or adding a P-ETR field to either Map-Notifys or Map-Replies.
5. Migration to LISP
This section discusses a deployment architecture to support the
migration to a LISP-enabled Internet. The loosely defined terms of
"early transition phase", "late transition phase", and "LISP Internet
phase" refer to time periods when LISP sites are a minority, a
majority, or represent all edge networks respectively.
5.1. LISP+BGP
For sites wishing to go LISP with their PI prefix the least
disruptive way is to upgrade their border routers to support LISP,
register the prefix into the LISP mapping system, but keep announcing
it with BGP as well. This way LISP sites will reach them over LISP,
while legacy sites will be unaffected by the change. The main
disadvantage of this approach is that no decrease in the DFZ routing
table size is achieved. Still, just increasing the number of LISP
sites is an important gain, as an increasing LISP/non-LISP site ratio
may decrease the need for BGP-based traffic engineering that leads to
prefix deaggregation. That, in turn, may lead to a decrease in the
DFZ size and churn in the late transition phase.
This scenario is not limited to sites that already have their
prefixes announced with BGP. Newly allocated EID blocks could follow
this strategy as well during the early LISP deployment phase,
depending on the cost/benefit analysis of the individual networks.
Since this leads to an increase in the DFZ size, the following
architecture should be preferred for new allocations.
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5.2. Mapping Service Provider (MSP) P-ITR Service
In addition to publishing their clients' registered prefixes in the
mapping system, MSPs with enough transit capacity can offer them
P-ITR service as a separate service. This service is especially
useful for new PI allocations, to sites without existing BGP
infrastructure, that wish to avoid BGP altogether. The MSP announces
the prefix into the DFZ, and the client benefits from ingress traffic
engineering without prefix deaggregation. The downside of this
scenario is adding path stretch.
Routing all non-LISP ingress traffic through a third party which is
not one of its ISPs is only feasible for sites with modest amounts of
traffic (like those using the IPv6 tunnel broker services today),
especially in the first stage of the transition to LISP, with a
significant number of legacy sites. This is because the handling of
said traffic is likely to result in additional costs, which would be
passed down to the client. When the LISP/non-LISP site ratio becomes
high enough, this approach can prove increasingly attractive.
Compared to LISP+BGP, this approach avoids DFZ bloat caused by prefix
deaggregation for traffic engineering purposes, resulting in slower
routing table increase in the case of new allocations and potential
decrease for existing ones. Moreover, MSPs serving different clients
with adjacent aggregatable prefixes may lead to additional decrease,
but quantifying this decrease is subject to future research study.
5.3. Proxy-ITR Route Distribution (PITR-RD)
Instead of a LISP site, or the MSP, announcing their EIDs with BGP to
the DFZ, this function can be outsourced to a third party, a P-ITR
Service Provider (PSP). This will result in a decrease of the
operational complexity both at the site and at the MSP.
The PSP manages a set of distributed P-ITR(s) that will advertise the
corresponding EID prefixes through BGP to the DFZ. These P-ITR(s)
will then encapsulate the traffic they receive for those EIDs towards
the RLOCs of the LISP site, ensuring their reachability from non-LISP
sites.
While it is possible for a PSP to manually configure each client's
EID routes to be announced, this approach offers little flexibility
and is not scalable. This section presents a scalable architecture
that offers automatic distribution of EID routes to LISP sites and
service providers.
The architecture requires no modification to existing LISP network
elements, but it introduces a new (conceptual) network element, the
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EID Route Server, defined as a router that either propagates routes
learned from other EID Route Servers, or it originates EID Routes.
The EID-Routes that it originates are those that it is authoritative
for. It propagates these routes to Proxy-ITRs within the AS of the
EID Route Server. It is worth to note that a BGP capable router can
be also considered as an EID Route Server.
Further, an EID-Route is defined as a prefix originated via the Route
Server of the mapping service provider, which should be aggregated if
the MSP has multiple customers inside a single large continuous
prefix. This prefix is propagated to other P-ITRs both within the
MSP and to other P-ITR operators it peers with. EID Route Servers
are operated either by the LISP site, MSPs or PSPs, and they may be
collocated with a Map Server or P-ITR, but are a functionally
discrete entity. They distribute EID-Routes, using BGP, to other
domains, according to policies set by participants.
MSP (AS64500)
RS ---> P-ITR
| /
| _.--./
,-'' /`--.
LISP site ---,' | v `.
( | DFZ )----- Mapping system
non-LISP site ----. | ^ ,'
`--. / _.-'
| `--''
v /
P-ITR
PSP (AS64501)
Figure 7: The P-ITR Route Distribution architecture
The architecture described above decouples EID origination from route
propagation, with the following benefits:
o Can accurately represent business relationships between P-ITR
operators
o More mapping system agnostic
o Minor changes to P-ITR implementation, no changes to other
components
In the example in the figure we have a MSP providing services to the
LISP site. The LISP site does not run BGP, and gets an EID
allocation directly from a RIR, or from the MSP, who may be a LIR.
Existing PI allocations can be migrated as well. The MSP ensures the
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presence of the prefix in the mapping system, and runs an EID Route
Server to distribute it to P-ITR service providers. Since the LISP
site does not run BGP, the prefix will be originated with the AS
number of the MSP.
In the simple case depicted in Figure 7 the EID-Route of LISP site
will be originated by the Route Server, and announced to the DFZ by
the PSP's P-ITRs with AS path 64501 64500. From that point on, the
usual BGP dynamics apply. This way, routes announced by P-ITR are
still originated by the authoritative Route Server. Note that the
peering relationships between MSP/PSPs and those in the underlying
forwarding plane may not be congruent, making the AS path to a P-ITR
shorter than it is in reality.
The non-LISP site will select the best path towards the EID-prefix,
according to its local BGP policies. Since AS-path length is usually
an important metric for selecting paths, a careful placement of P-ITR
could significantly reduce path-stretch between LISP and non-LISP
sites.
The architecture allows for flexible policies between MSP/PSPs.
Consider the EID Route Server networks as control plane overlays,
facilitating the implementation of policies necessary to reflect the
business relationships between participants. The results are then
injected to the common underlying forwarding plane. For example,
some MSP/PSPs may agree to exchange EID-Prefixes and only announce
them to each of their forwarding plane customers. Global
reachability of an EID-prefix depends on the MSP the LISP site buys
service from, and is also subject to agreement between the mentioned
parties.
In terms of impact on the DFZ, this architecture results in a slower
routing table increase for new allocations, since traffic engineering
will be done at the LISP level. For existing allocations migrating
to LISP, the DFZ may decrease since MSPs may be able to aggregate the
prefixes announced.
Compared to LISP+BGP, this approach avoids DFZ bloat caused by prefix
deaggregation for traffic engineering purposes, resulting in slower
routing table increase in the case of new allocations and potential
decrease for existing ones. Moreover, MSPs serving different clients
with adjacent aggregatable prefixes may lead to additional decrease,
but quantifying this decrease is subject to future research study.
The flexibility and scalability of this architecture does not come
without a cost however: A PSP operator has to establish either
transit or peering relationships to improve their connectivity.
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5.4. Migration Summary
Registering a domain name typically entails an annual fee that should
cover the operating expenses for publishing the domain in the global
DNS. The situation is similar with several other registration
services. A LISP mapping service provider (MSR) client publishing an
EID prefix in the LISP mapping system has the option of signing up
for PITR services as well, for an extra fee. These services may be
offered by the MSP itself, but it is expected that specialized P-ITR
service providers (PSPs) will do it. Clients not signing up become
responsible for getting non-LISP traffic to their EIDs (using the
LISP+BGP scenario).
Additionally, Tier 1 ISPs have incentives to offer P-ITR services to
non-subscribers in strategic places just to attract more traffic from
competitors, thus more revenue.
The following table presents the expected effects of the different
transition scenarios during a certain phase on the DFZ routing table
size:
Phase | LISP+BGP | MSP P-ITR | PITR-RD
-----------------+--------------+-----------------+----------------
Early transition | no change | slower increase | slower increase
Late transition | may decrease | slower increase | slower increase
LISP Internet | considerable decrease
It is expected that PITR-RD will co-exist with LISP+BGP during the
migration, with the latter being more popular in the early transition
phase. As the transition progresses and the MSP P-ITR and PITR-RD
ecosystem gets more ubiquitous, LISP+BGP should become less
attractive, slowing down the increase of the number of routes in the
DFZ.
Note that throughout Section 5 we focused on the effects of LISP
deployment on the DFZ route table size. Other metrics may be
impacted as well, but to the best of our knowlegde have not been
measured as of yet.
6. Security Considerations
All security implications of LISP deployments are to be discussed in
separate documents. [I-D.ietf-lisp-threats] gives an overview of
LISP threat models, including ETR operators attracting traffic by
overclaiming an EID-prefix (Section 4.4.3). Securing mapping lookups
is discussed in [I-D.ietf-lisp-sec].
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7. IANA Considerations
This memo includes no request to IANA.
8. Acknowledgements
Many thanks to Margaret Wasserman for her contribution to the IETF76
presentation that kickstarted this work. The authors would also like
to thank Damien Saucez, Luigi Iannone, Joel Halpern, Vince Fuller,
Dino Farinacci, Terry Manderson, Noel Chiappa, Hannu Flinck, Paul
Vinciguerra, Fred Templin, Brian Haberman, and everyone else who
provided input.
9. References
9.1. Normative References
[RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
Locator/ID Separation Protocol (LISP)", RFC 6830,
January 2013.
[RFC6832] Lewis, D., Meyer, D., Farinacci, D., and V. Fuller,
"Interworking between Locator/ID Separation Protocol
(LISP) and Non-LISP Sites", RFC 6832, January 2013.
[RFC6833] Fuller, V. and D. Farinacci, "Locator/ID Separation
Protocol (LISP) Map-Server Interface", RFC 6833,
January 2013.
9.2. Informative References
[CACHE] Jung, J., Sit, E., Balakrishnan, H., and R. Morris, "DNS
performance and the effectiveness of caching", 2002.
[DDT-ROOT]
"DDT Root", <http://ddt-root.org/>.
[I-D.ietf-lisp-ddt]
Fuller, V., Lewis, D., Ermagan, V., and A. Jain, "LISP
Delegated Database Tree", draft-ietf-lisp-ddt-01 (work in
progress), March 2013.
[I-D.ietf-lisp-sec]
Maino, F., Ermagan, V., Cabellos-Aparicio, A., Saucez, D.,
and O. Bonaventure, "LISP-Security (LISP-SEC)",
draft-ietf-lisp-sec-05 (work in progress), October 2013.
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[I-D.ietf-lisp-threats]
Saucez, D., Iannone, L., and O. Bonaventure, "LISP Threats
Analysis", draft-ietf-lisp-threats-08 (work in progress),
October 2013.
[RFC4459] Savola, P., "MTU and Fragmentation Issues with In-the-
Network Tunneling", RFC 4459, April 2006.
[RFC4786] Abley, J. and K. Lindqvist, "Operation of Anycast
Services", BCP 126, RFC 4786, December 2006.
[RFC4984] Meyer, D., Zhang, L., and K. Fall, "Report from the IAB
Workshop on Routing and Addressing", RFC 4984,
September 2007.
[RFC6834] Iannone, L., Saucez, D., and O. Bonaventure, "Locator/ID
Separation Protocol (LISP) Map-Versioning", RFC 6834,
January 2013.
[RFC6836] Fuller, V., Farinacci, D., Meyer, D., and D. Lewis,
"Locator/ID Separation Protocol Alternative Logical
Topology (LISP+ALT)", RFC 6836, January 2013.
[RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
Selkirk, "Port Control Protocol (PCP)", RFC 6887,
April 2013.
[TELCO96] "Telecommunications Act of 1996", 1996.
Appendix A. Step-by-Step Example BGP to LISP Migration Procedure
To help the operational community deploy LISP, this informative
section offers a step-by-step guide for migrating a BGP based
Internet presence to a LISP site. It includes a pre-install/
pre-turn-up checklist, and customer and provider activation
procedures.
A.1. Customer Pre-Install and Pre-Turn-up Checklist
1. Determine how many current physical service provider connections
the customer has and their existing bandwidth and traffic
engineering requirements.
This information will determine the number of routing locators,
and the priorities and weights that should be configured on the
xTRs.
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2. Make sure customer router has LISP capabilities.
* Check OS version of the CE router. If LISP is an add-on,
check if it is installed.
This information can be used to determine if the platform is
appropriate to support LISP, in order to determine if a
software and/or hardware upgrade is required.
* Have customer upgrade (if necessary, software and/or hardware)
to be LISP capable.
3. Obtain current running configuration of CE router. A suggested
LISP router configuration example can be customized to the
customer's existing environment.
4. Verify MTU Handling
* Request increase in MTU to 1556 or more on service provider
connections. Prior to MTU change verify that 1500 byte packet
from P-xTR to RLOC with do not fragment (DF-bit) bit set.
* Ensure they are not filtering ICMP unreachable or time-
exceeded on their firewall or router.
LISP, like any tunneling protocol, will increase the size of
packets when the LISP header is appended. If increasing the MTU
of the access links is not possible, care must be taken that ICMP
is not being filtered in order to allow for Path MTU Discovery to
take place.
5. Validate member prefix allocation.
This step is to check if the prefix used by the customer is a
direct (Provider Independent), or if it is a prefix assigned by a
physical service provider (Provider Aggregatable). If the
prefixes are assigned by other service providers then a Letter of
Agreement is required to announce prefixes through the Proxy
Service Provider.
6. Verify the member RLOCs and their reachability.
This step ensures that the RLOCs configured on the CE router are
in fact reachable and working.
7. Prepare for cut-over.
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* If possible, have a host outside of all security and filtering
policies connected to the console port of the edge router or
switch.
* Make sure customer has access to the router in order to
configure it.
A.2. Customer Activating LISP Service
1. Customer configures LISP on CE router(s) from service provider
recommended configuration.
The LISP configuration consists of the EID prefix, the locators,
and the weights and priorities of the mapping between the two
values. In addition, the xTR must be configured with Map
Resolver(s), Map Server(s) and the shared key for registering to
Map Server(s). If required, Proxy-ETR(s) may be configured as
well.
In addition to the LISP configuration, the following:
* Ensure default route(s) to next-hop external neighbors are
included and RLOCs are present in configuration.
* If two or more routers are used, ensure all RLOCs are included
in the LISP configuration on all routers.
* It will be necessary to redistribute default route via IGP
between the external routers.
2. When transition is ready perform a soft shutdown on existing eBGP
peer session(s)
* From CE router, use LIG to ensure registration is successful.
* To verify LISP connectivity, find and ping LISP connected
sites. If possible, find ping destinations that are not
covered by a prefix in the global BGP routing system, because
PITRs may deliver the packets even if LISP connectivity is not
working. Traceroutes may help discover if this is the case.
* To verify connectivity to non-LISP sites, try accessing a
landmark (e.g., a major Internet site) via a web browser.
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A.3. Cut-Over Provider Preparation and Changes
1. Verify site configuration and then active registration on Map
Server(s)
* Authentication key
* EID prefix
2. Add EID space to map-cache on proxies
3. Add networks to BGP advertisement on proxies
* Modify route-maps/policies on P-xTRs
* Modify route policies on core routers (if non-connected
member)
* Modify ingress policers on core routers
* Ensure route announcement in looking glass servers, RouteViews
4. Perform traffic verification test
* Ensure MTU handling is as expected (PMTUD working)
* Ensure proxy-ITR map-cache population
* Ensure access from traceroute/ping servers around Internet
* Use a looking glass, to check for external visibility of
registration via several Map Resolvers
Authors' Addresses
Lorand Jakab
Cisco Systems
170 Tasman Drive
San Jose, CA 95134
USA
Email: lojakab@cisco.com
Jakab, et al. Expires July 21, 2014 [Page 27]
Internet-Draft LISP Deployment January 2014
Albert Cabellos-Aparicio
Technical University of Catalonia
C/Jordi Girona, s/n
BARCELONA 08034
Spain
Email: acabello@ac.upc.edu
Florin Coras
Technical University of Catalonia
C/Jordi Girona, s/n
BARCELONA 08034
Spain
Email: fcoras@ac.upc.edu
Jordi Domingo-Pascual
Technical University of Catalonia
C/Jordi Girona, s/n
BARCELONA 08034
Spain
Email: jordi.domingo@ac.upc.edu
Darrel Lewis
Cisco Systems
170 Tasman Drive
San Jose, CA 95134
USA
Email: darlewis@cisco.com
Jakab, et al. Expires July 21, 2014 [Page 28]
