The Locator/ID Separation Protocol (LISP)Cisco SystemsTasman DriveSan JoseCA95134USAfarinacci@gmail.comCisco SystemsTasman DriveSan JoseCA95134USAvince.fuller@gmail.comCisco Systems170 Tasman DriveSan JoseCAUSAdmm@1-4-5.netCisco Systems170 Tasman DriveSan JoseCAUSAdarlewis@cisco.comUPC/BarcelonaTechCampus Nord, C. Jordi Girona 1-3BarcelonaCatalunyaSpainacabello@ac.upc.eduThis document describes the data-plane protocol for the
Locator/ID Separation Protocol (LISP). LISP defines two
namespaces, End-point Identifiers (EIDs) that identify end-hosts
and Routing Locators (RLOCs) that identify network attachment
points. With this, LISP effectively separates control from data,
and allows routers to create overlay networks. LISP-capable
routers exchange encapsulated packets according to EID-to-RLOC
mappings stored in a local map-cache.LISP requires no change to either host protocol stacks or
to underlay routers and offers Traffic Engineering,
multihoming and mobility, among other features.This document describes the Locator/Identifier Separation
Protocol (LISP). LISP is an encapsulation protocol built around the
fundamental idea of separating the topological location of a network
attachment point from the node's identity . As a result LISP creates two namespaces: Endpoint Identifiers
(EIDs), that are used to identify end-hosts (e.g., nodes or Virtual
Machines) and routable Routing Locators (RLOCs), used to identify
network attachment points. LISP then defines functions for mapping
between the two namespaces and for encapsulating traffic
originated by devices using non-routable EIDs for transport across a
network infrastructure that routes and forwards using RLOCs. LISP
encapsulation uses a dynamic form of tunneling where no static provisioning
is required or necessary.LISP is an overlay protocol that separates control from
data-plane, this document specifies the data-plane, how LISP-capable
routers (Tunnel Routers) exchange packets by encapsulating them to
the appropriate location. Tunnel routers are equipped with a cache,
called map-cache, that contains EID-to-RLOC mappings. The map-cache
is populated using the LISP Control-Plane protocol .LISP does not require changes to either host protocol stack or to
underlay routers. By separating the EID from the RLOC space, LISP
offers native Traffic Engineering, multihoming and mobility, among
other features.Creation of LISP was initially motivated by discussions during
the IAB-sponsored Routing and Addressing Workshop held in Amsterdam
in October 2006 (see ).This document specifies the LISP data-plane encapsulation and
other LISP forwarding node functionality while specifies the LISP control
plane. LISP deployment guidelines can be found in and describes
considerations for network operational management. Finally, describes the LISP architecture.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 .AFI is a term used
to describe an address encoding in a packet. An address family
that pertains to the data-plane. See and
for details. An AFI value of 0 used in
this specification indicates an unspecified encoded address where
the length of the address is 0 octets following the 16-bit AFI
value of 0.Anycast Address is a term used in
this document to refer to the same IPv4 or IPv6 address configured
and used on multiple systems at the same time. An EID or RLOC can
be an anycast address in each of their own address spaces.Client-side is a term used in this
document to indicate a connection initiation attempt by an end-system
represented by an EID.A Data-Probe is a LISP-encapsulated
data packet where the inner-header destination address equals the
outer-header destination address used to trigger a Map-Reply by a
decapsulating ETR. In addition, the original packet is
decapsulated and delivered to the destination host if the
destination EID is in the EID-Prefix range configured on the
ETR. Otherwise, the packet is discarded. A Data-Probe is used in
some of the mapping database designs to "probe" or request a
Map-Reply from an ETR; in other cases, Map-Requests are used. See
each mapping database design for details. When using Data-Probes,
by sending Map-Requests on the underlying routing system,
EID-Prefixes must be advertised.An ETR is a router that
accepts an IP packet where the 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. ETR functionality does not
have to be limited to a router device. A server host can be the
endpoint of a LISP tunnel as well.The EID-to-RLOC Database is a
global distributed database that contains all known
EID-Prefix-to-RLOC mappings. Each potential ETR typically
contains a small piece of the database: the EID-to-RLOC mappings
for the EID-Prefixes "behind" the router. These map to one of the
router's own globally visible IP addresses.
Note that there MAY be transient conditions when the EID-Prefix
for the site and Locator-Set for each EID-Prefix may not be the
same on all ETRs. This has no negative implications, since a
partial set of Locators can be used.The EID-to-RLOC map-cache is
generally short-lived, on-demand table in an ITR that stores, tracks, and
is responsible for timing out and otherwise validating EID-to-RLOC
mappings. This cache is distinct from the full "database" of
EID-to-RLOC mappings; it is dynamic, local to the ITR(s), and
relatively small, while the database is distributed, relatively
static, and much more global in scope.An EID-Prefix is a power-of-two block
of EIDs that are allocated to a site by an address allocation
authority. EID-Prefixes are associated with a set of RLOC
addresses. EID-Prefix allocations can be broken up into smaller
blocks when an RLOC set is to be associated with the larger
EID-Prefix block.An end-system is an IPv4 or IPv6 device
that originates packets with a single IPv4 or IPv6 header. The
end-system supplies an EID value for the destination address field
of the IP header when communicating globally (i.e., outside of its
routing domain). An end-system can be a host computer, a switch
or router device, or any network appliance.An EID is a 32-bit (for IPv4) or
128-bit (for IPv6) value used in the source and destination
address fields of the first (most inner) LISP header of a
packet. The host obtains a destination EID the same way it obtains
a destination address today, for example, through a Domain Name
System (DNS) lookup or Session
Initiation Protocol (SIP) exchange. The
source EID is obtained via existing mechanisms used to set a
host's "local" IP address. An EID used on the public Internet MUST
have the same properties as any other IP address used in that
manner; this means, among other things, that it MUST be globally
unique. An EID is allocated to a host from an EID-Prefix block
associated with the site where the host is located. An EID can be
used by a host to refer to other hosts. Note that EID blocks MAY
be assigned in a hierarchical manner, independent of the network
topology, to facilitate scaling of the mapping database. In
addition, an EID block assigned to a site MAY have site-local
structure (subnetting) for routing within the site; this structure
is not visible to the global routing system. In theory, the bit
string that represents an EID for one device can represent an RLOC
for a different device. When used in discussions with other
Locator/ID separation proposals, a LISP EID will be called an
"LEID". Throughout this document, any references to "EID" refer to
an LEID.An ITR is a router
that resides in a LISP site. Packets sent by sources inside of the
LISP site to destinations outside of the site are candidates for
encapsulation by the ITR. The ITR treats the 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 routable
RLOCs (in the RLOC space) 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
device that has better knowledge of the EID-to-RLOC mapping closer
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.Specifically, when a service provider prepends a LISP header
for Traffic Engineering purposes, the router that does this is
also regarded as an ITR. The outer RLOC the ISP ITR uses can be
based on the outer destination address (the originating ITR's
supplied RLOC) or the inner destination address (the originating
host's supplied EID).LISP header is a term used in this
document to refer to the outer IPv4 or IPv6 header, a UDP header,
and a LISP-specific 8-octet header that follow the UDP header and
that an ITR prepends or an ETR strips.A LISP router is a router that
performs the functions of any or all of the following: ITR, ETR, RTR,
Proxy-ITR (PITR), or Proxy-ETR (PETR).LISP site is a set of routers in an edge
network that are under a single technical administration. LISP
routers that reside in the edge network are the demarcation points
to separate the edge network from the core network. Locator-Status-Bits are
present in the LISP header. They are used by ITRs to inform ETRs
about the up/down status of all ETRs at the local site. These bits
are used as a hint to convey up/down router status and not path
reachability status. The LSBs can be verified by use of one of the
Locator reachability algorithms described in .A negative mapping entry,
also known as a negative cache entry, is an EID-to-RLOC entry
where an EID-Prefix is advertised or stored with no RLOCs. That
is, the Locator-Set for the EID-to-RLOC entry is empty or has an
encoded Locator count of 0. This type of entry could be used to
describe a prefix from a non-LISP site, which is explicitly not in
the mapping database. There are a set of well-defined actions that
are encoded in a Negative Map-Reply.A PETR is defined and described
in . A PETR acts like an ETR but does so
on behalf of LISP sites that send packets to destinations at
non-LISP sites.A PITR is defined and described
in . A PITR acts like an ITR but does so
on behalf of non-LISP sites that send packets to destinations at
LISP sites.Recursive Tunneling occurs
when a packet has more than one LISP IP header. Additional layers
of tunneling MAY be employed to implement Traffic Engineering or
other re-routing as needed. When this is done, an additional
"outer" LISP header is added, and the original RLOCs are preserved
in the "inner" header.
An RTR acts like an ETR to remove a LISP header, then acts as an
ITR to prepend a new LISP header. This is known as
Re-encapsulating Tunneling. Doing this allows a packet to be
re-routed by the RTR without adding the overhead of additional
tunnel headers. When using multiple mapping database systems, care
must be taken to not create re- encapsulation loops through
misconfiguration.Route-returnability is an
assumption that the underlying routing system will deliver packets
to the destination. When combined with a nonce that is provided by
a sender and returned by a receiver, this limits off-path data
insertion. A route-returnability check is verified when a message
is sent with a nonce, another message is returned with the same
nonce, and the destination of the original message appears as the
source of the returned message.An RLOC is an IPv4 or IPv6 address of
an Egress Tunnel Router (ETR). An RLOC is the output of an
EID-to-RLOC mapping lookup. An EID maps to zero or more
RLOCs. Typically, RLOCs are numbered from blocks that
are assigned to a site at each point to which it attaches to the
underlay network; where the topology is defined by the connectivity
of provider networks. Multiple RLOCs can be assigned to the same
ETR device or to multiple ETR devices at a site.Server-side is a term used in this
document to indicate that a connection initiation attempt is being
accepted for a destination EID.A TE-ETR is an ETR that is deployed in a
service provider network that strips an outer LISP header for
Traffic Engineering purposes.A TE-ITR is an ITR that is deployed in a
service provider network that prepends an additional LISP header
for Traffic Engineering purposes.An xTR is a reference to an ITR or ETR when
direction of data flow is not part of the context description.
"xTR" refers to the router that is the tunnel endpoint and is used
synonymously with the term "Tunnel Router". For example, "An xTR
can be located at the Customer Edge (CE) router" indicates both
ITR and ETR functionality at the CE router.One key concept of LISP is that end-systems operate the same way
they do today. The IP addresses that hosts use for tracking sockets
and connections, and for sending and receiving packets, do not
change. In LISP terminology, these IP addresses are called Endpoint
Identifiers (EIDs).Routers continue to forward packets based on IP destination
addresses. When a packet is LISP encapsulated, these addresses are
referred to as Routing Locators (RLOCs). Most routers along a path
between two hosts will not change; they continue to perform
routing/forwarding lookups on the destination addresses. For routers
between the source host and the ITR as well as routers from the ETR
to the destination host, the destination address is an EID. For the
routers between the ITR and the ETR, the destination address is an
RLOC.Another key LISP concept is the "Tunnel Router". A Tunnel Router
prepends LISP headers on host-originated packets and strips them
prior to final delivery to their destination. The IP addresses in
this "outer header" are RLOCs. During end-to-end packet
exchange between two Internet hosts, an ITR prepends a new LISP
header to each packet, and an ETR strips the new header. The ITR
performs EID-to-RLOC lookups to determine the routing path to the
ETR, which has the RLOC as one of its IP addresses. Some basic rules governing LISP are:End-systems only send to addresses that are EIDs. EIDs are
typically IP addresses assigned to hosts (other types of EID are
supported by LISP, see for further
information). End-systems don't know that addresses are EIDs
versus RLOCs but assume that packets get to their intended
destinations. In a system where LISP is deployed, LISP routers
intercept EID-addressed packets and assist in delivering them
across the network core where EIDs cannot be routed. The
procedure a host uses to send IP packets does not change.LISP routers mostly deal with Routing Locator addresses. See
details in to clarify what is meant by
"mostly".RLOCs are always IP addresses assigned to routers, preferably
topologically oriented addresses from provider CIDR (Classless
Inter-Domain Routing) blocks. When a router originates packets, it MAY use as a source
address either an EID or RLOC. When acting as a host (e.g., when
terminating a transport session such as Secure SHell (SSH),
TELNET, or the Simple Network Management Protocol (SNMP)), it
MAY use an EID that is explicitly assigned for that purpose. An
EID that identifies the router as a host MUST NOT be used as an
RLOC; an EID is only routable within the scope of a site. A
typical BGP configuration might demonstrate this "hybrid"
EID/RLOC usage where a router could use its "host-like" EID to
terminate iBGP sessions to other routers in a site while at the
same time using RLOCs to terminate eBGP sessions to routers
outside the site.Packets with EIDs in them are not expected to be delivered
end-to-end in the absence of an EID-to-RLOC mapping
operation. They are expected to be used locally for intra-site
communication or to be encapsulated for inter-site
communication.EIDs MAY also be structured (subnetted) in a manner suitable
for local routing within an Autonomous System (AS).An additional LISP header MAY be prepended to packets by a
TE-ITR when re-routing of the path for a packet is desired. A
potential use-case for this would be an ISP router that needs to
perform Traffic Engineering for packets flowing through its
network. In such a situation, termed "Recursive Tunneling", an ISP
transit acts as an additional ITR, and the RLOC it uses for the
new prepended header would be either a TE-ETR within the ISP
(along an intra-ISP traffic engineered path) or a TE-ETR within
another ISP (an inter-ISP traffic engineered path, where an
agreement to build such a path exists). In order to avoid excessive packet overhead as well as possible
encapsulation loops, this document recommends that a maximum of two
LISP headers can be prepended to a packet. For initial LISP
deployments, it is assumed that two headers is sufficient, where
the first prepended header is used at a site for Location/Identity
separation and the second prepended header is used inside a
service provider for Traffic Engineering purposes.Tunnel Routers can be placed fairly flexibly in a multi-AS
topology. For example, the ITR for a particular end-to-end packet
exchange might be the first-hop or default router within a site
for the source host. Similarly, the ETR might be the last-hop
router directly connected to the destination host. Another
example, perhaps for a VPN service outsourced to an ISP by a site,
the ITR could be the site's border router at the service
provider attachment point. Mixing and matching of site-operated,
ISP-operated, and other Tunnel Routers is allowed for maximum
flexibility. This section provides an example of the unicast packet flow,
including also control-plane information as specified in . The example also assumes
the following conditions:Source host "host1.abc.example.com" is sending a
packet to "host2.xyz.example.com", exactly what
host1 would do if the site was not using LISP.Each site is multihomed, so each Tunnel Router has an
address (RLOC) assigned from the service provider address
block for each provider to which that particular Tunnel Router
is attached.The ITR(s) and ETR(s) are directly connected to the source
and destination, respectively, but the source and destination
can be located anywhere in the LISP site.A Map-Request is sent for an external destination when the
destination is not found in the forwarding table or matches a
default route. Map-Requests are sent to the mapping database
system by using the LISP control-plane protocol documented in
.Map-Replies are sent on the underlying routing system
topology using the
control-plane protocol.Client host1.abc.example.com wants to communicate with
server host2.xyz.example.com:host1.abc.example.com wants to open a TCP connection to
host2.xyz.example.com. It does a DNS lookup on
host2.xyz.example.com. An A/AAAA record is returned. This
address is the destination EID. The locally assigned address
of host1.abc.example.com is used as the source EID. An IPv4
or IPv6 packet is built and forwarded through the LISP site
as a normal IP packet until it reaches a LISP ITR.The LISP ITR must be able to map the destination EID to an
RLOC of one of the ETRs at the destination site. The specific
method used to do this is not described in this example. See
for further
information.The ITR sends a LISP Map-Request as specified in . Map-Requests SHOULD be
rate-limited.The mapping system helps forwarding the Map-Request to the
corresponding ETR. When the Map-Request arrives at one of the
ETRs at the destination site, it will process the packet as a
control message.The ETR looks at the destination EID of the Map-Request
and matches it against the prefixes in the ETR's configured
EID-to-RLOC mapping database. This is the list of
EID-Prefixes the ETR is supporting for the site it resides
in. If there is no match, the Map-Request is
dropped. Otherwise, a LISP Map-Reply is returned to the
ITR.The ITR receives the Map-Reply message, parses the message
(to check for format validity), and stores the mapping
information from the packet. This information is stored in
the ITR's EID-to-RLOC map-cache. Note that the
map-cache is an on-demand cache. An ITR will manage its
map-cache in such a way that optimizes for its resource
constraints.Subsequent packets from host1.abc.example.com to
host2.xyz.example.com will have a LISP header prepended by
the ITR using the appropriate RLOC as the LISP header
destination address learned from the ETR. Note that the
packet MAY be sent to a different ETR than the one that
returned the Map-Reply due to the source site's hashing
policy or the destination site's Locator-Set policy.The ETR receives these packets directly (since the
destination address is one of its assigned IP addresses),
checks the validity of the addresses, strips the LISP header,
and forwards packets to the attached destination host.In order to defer the need for a mapping lookup in the
reverse direction, an ETR can OPTIONALLY create a cache entry
that maps the source EID (inner-header source IP address) to
the source RLOC (outer-header source IP address) in a
received LISP packet. Such a cache entry is termed a
"glean mapping" and only contains a single RLOC for the EID
in question. More complete information about additional
RLOCs SHOULD be verified by sending a LISP Map-Request for
that EID. Both the ITR and the ETR MAY also influence the
decision the other makes in selecting an RLOC.Since additional tunnel headers are prepended, the packet
becomes larger and can exceed the MTU of any link traversed from
the ITR to the ETR. It is RECOMMENDED in IPv4 that packets do not
get fragmented as they are encapsulated by the ITR. Instead, the
packet is dropped and an ICMP Unreachable/Fragmentation-Needed
message is returned to the source.In the case when fragmentation is needed, this specification
RECOMMENDS that implementations provide support for one of the
proposed fragmentation and reassembly schemes. Two existing
schemes are detailed in .Since IPv4 or IPv6 addresses can be either EIDs or RLOCs, the
LISP architecture supports IPv4 EIDs with IPv6 RLOCs (where the
inner header is in IPv4 packet format and the outer header is in
IPv6 packet format) or IPv6 EIDs with IPv4 RLOCs (where the inner
header is in IPv6 packet format and the outer header is in IPv4
packet format). The next sub-sections illustrate packet formats
for the homogeneous case (IPv4-in-IPv4 and IPv6-in-IPv6), but all
4 combinations MUST be supported. Additional types of EIDs are
defined in .The inner header is the header on the datagram
received from the originating host . The
source and destination IP addresses are EIDs.The outer header is a new
header prepended by an ITR. The address fields contain RLOCs
obtained from the ingress router's EID-to-RLOC Cache. The IP
protocol number is "UDP (17)" from . The setting of the Don't Fragment (DF)
bit 'Flags' field is according to rules listed in Sections
and .The UDP header contains an ITR
selected source port when encapsulating a packet. See for details on the hash algorithm used
to select a source port based on the 5-tuple of the inner
header. The destination port MUST be set to the well-known
IANA-assigned port value 4341.The 'UDP Checksum' field SHOULD
be transmitted as zero by an ITR for either IPv4 and IPv6 encapsulation . When a
packet with a zero UDP checksum is received by an ETR, the
ETR MUST accept the packet for decapsulation. When an ITR
transmits a non-zero value for the UDP checksum, it MUST
send a correctly computed value in this field. When an ETR
receives a packet with a non-zero UDP checksum, it MAY
choose to verify the checksum value. If it chooses to
perform such verification, and the verification fails, the
packet MUST be silently dropped. If the ETR chooses not to
perform the verification, or performs the verification
successfully, the packet MUST be accepted for
decapsulation. The handling of UDP zero checksums over IPv6
for all tunneling protocols, including LISP, is subject to
the applicability statement in .The 'UDP Length' field is set for
an IPv4-encapsulated packet to be the sum of the
inner-header IPv4 Total Length plus the UDP and LISP header
lengths. For an IPv6-encapsulated packet, the 'UDP Length'
field is the sum of the inner-header IPv6 Payload Length,
the size of the IPv6 header (40 octets), and the size of the
UDP and LISP headers.The N-bit is the nonce-present bit. When
this bit is set to 1, the low-order 24 bits of the first 32
bits of the LISP header contain a Nonce. See for details. Both N- and V-bits MUST
NOT be set in the same packet. If they are, a decapsulating
ETR MUST treat the 'Nonce/Map-Version' field as having a
Nonce value present.The L-bit is the 'Locator-Status-Bits'
field enabled bit. When this bit is set to 1, the
Locator-Status-Bits in the second 32 bits of the LISP
header are in use.The E-bit is the echo-nonce-request bit.
This bit MUST be ignored and has no meaning when the N-bit
is set to 0. When the N-bit is set to 1 and this bit is set
to 1, an ITR is requesting that the nonce value in the
'Nonce' field be echoed back in LISP-encapsulated packets
when the ITR is also an ETR. See
for details.The V-bit is the Map-Version present
bit. When this bit is set to 1, the N-bit MUST be 0. Refer
to for more details. This
bit indicates that the LISP header is encoded in this
case as:The I-bit is the Instance ID bit. See for more details. When this bit is set
to 1, the 'Locator-Status-Bits' field is reduced to 8 bits
and the high-order 24 bits are used as an Instance ID. If
the L-bit is set to 0, then the low-order 8 bits are
transmitted as zero and ignored on receipt. The format of
the LISP header would look like this:The R-bit is a Reserved bit for future
use. It MUST be set to 0 on transmit and MUST be ignored on
receipt.The KK-bits are a 2-bit field used when
encapsulated packets are encrypted. The field is set to 00
when the packet is not encrypted. See for further information.The LISP 'Nonce' field is a 24-bit
value that is randomly generated by an ITR when the N-bit is
set to 1. Nonce generation algorithms are an implementation
matter but are required to generate different nonces when
sending to different destinations. However, the same nonce
can be used for a period of time when encapsulating to the
same ETR. The nonce is also used when the E-bit is set to
request the nonce value to be echoed by the other side when
packets are returned. When the E-bit is clear but the N-bit
is set, a remote ITR is either echoing a previously
requested echo-nonce or providing a random nonce. See for more details.When the
L-bit is also set, the 'Locator-Status-Bits' field in the
LISP header is set by an ITR to indicate to an ETR the
up/down status of the Locators in the source site. Each RLOC
in a Map-Reply is assigned an ordinal value from 0 to n-1
(when there are n RLOCs in a mapping entry). The
Locator-Status-Bits are numbered from 0 to n-1 from the
least significant bit of the field. The field is 32 bits
when the I-bit is set to 0 and is 8 bits when the I-bit is
set to 1. When a Locator-Status-Bit is set to 1, the ITR is
indicating to the ETR that the RLOC associated with the bit
ordinal has up status. See for
details on how an ITR can determine the status of the ETRs
at the same site. When a site has multiple EID-Prefixes
that result in multiple mappings (where each could have a
different Locator-Set), the Locator-Status-Bits setting in
an encapsulated packet MUST reflect the mapping for the
EID-Prefix that the inner-header source EID address
matches. If the LSB for an anycast Locator is set to 1, then
there is at least one RLOC with that address, and the ETR is
considered 'up'.When doing ITR/PITR encapsulation:The outer-header 'Time to Live' field (or 'Hop Limit'
field, in the case of IPv6) SHOULD be copied from the
inner-header 'Time to Live' field. The outer-header 'Differentiated Services Code Point'
(DSCP) field (or the 'Traffic Class' field, in the case of
IPv6) SHOULD be copied from the inner-header DSCP field
('Traffic Class' field, in the case of IPv6) considering
the exception listed below.The 'Explicit Congestion Notification' (ECN) field (bits
6 and 7 of the IPv6 'Traffic Class' field) requires special
treatment in order to avoid discarding indications of
congestion . ITR encapsulation MUST
copy the 2-bit 'ECN' field from the inner header to the
outer header. Re-encapsulation MUST copy the 2-bit 'ECN'
field from the stripped outer header to the new outer
header.When doing ETR/PETR decapsulation:The inner-header 'Time to Live' field (or 'Hop Limit'
field, in the case of IPv6) SHOULD be copied from the
outer-header 'Time to Live' field, when the Time to Live
value of the outer header is less than the Time to Live
value of the inner header. Failing to perform this check
can cause the Time to Live of the inner header to increment
across encapsulation/decapsulation cycles. This check is
also performed when doing initial encapsulation, when a
packet comes to an ITR or PITR destined for a LISP site.The inner-header 'Differentiated Services Code Point'
(DSCP) field (or the 'Traffic Class' field, in the case of
IPv6) SHOULD be copied from the outer-header DSCP field
('Traffic Class' field, in the case of IPv6) considering the
exception listed below.The 'Explicit Congestion Notification' (ECN) field (bits
6 and 7 of the IPv6 'Traffic Class' field) requires special
treatment in order to avoid discarding indications of
congestion . If the 'ECN' field
contains a congestion indication codepoint (the value is
'11', the Congestion Experienced (CE) codepoint), then ETR
decapsulation MUST copy the 2-bit 'ECN' field from the
stripped outer header to the surviving inner header that is
used to forward the packet beyond the ETR. These
requirements preserve CE indications when a packet that uses
ECN traverses a LISP tunnel and becomes marked with a CE
indication due to congestion between the tunnel
endpoints.Note that if an ETR/PETR is also an ITR/PITR and chooses to
re-encapsulate after decapsulating, the net effect of this
is that the new outer header will carry the same Time to
Live as the old outer header minus 1.Copying the Time to Live (TTL) serves two purposes:
first, it preserves the distance the host intended the packet to
travel; second, and more importantly, it provides for
suppression of looping packets in the event there is a loop of
concatenated tunnels due to misconfiguration.The Explicit Congestion Notification ('ECN') field occupies
bits 6 and 7 of both the IPv4 'Type of Service' field and the
IPv6 'Traffic Class' field . The
'ECN' field requires special treatment in order to avoid
discarding indications of congestion . An ITR/PITR encapsulation MUST copy the 2-bit 'ECN' field
from the inner header to the outer header. Re-encapsulation
MUST copy the 2-bit 'ECN' field from the stripped outer header
to the new outer header. If the 'ECN' field contains a
congestion indication codepoint (the value is '11', the
Congestion Experienced (CE) codepoint), then ETR/PETR
decapsulation MUST copy the 2-bit 'ECN' field from the
stripped outer header to the surviving inner header that is
used to forward the packet beyond the ETR. These requirements
preserve CE indications when a packet that uses ECN traverses
a LISP tunnel and becomes marked with a CE indication due to
congestion between the tunnel endpoints.ITRs and PITRs maintain an on-demand cache, referred as LISP
EID-to-RLOC Map-Cache, that contains mappings from EID-prefixes
to locator sets. The cache is used to encapsulate packets from
the EID space to the corresponding RLOC network attachment point.When an ITR/PITR receives a packet from inside of the LISP
site to destinations outside of the site a longest-prefix match
lookup of the EID is done to the map-cache.When the lookup succeeds, the Locator-Set retrieved from the
map-cache is used to send the packet to the EID's topological
location.If the lookup fails, the ITR/PITR needs to retrieve the
mapping using the LISP control-plane protocol . The mapping is then stored
in the local map-cache to forward subsequent packets addressed to
the same EID-prefix.The map-cache is a local cache of mappings, entries are
expired based on the associated Time to live. In addition,
entries can be updated with more current information, see for further information on
this. Finally, the map-cache also contains reachability
information about EIDs and RLOCs, and uses LISP reachability
information mechanisms to determine the reachability of RLOCs,
see for the specific mechanisms.This section proposes two mechanisms to deal with
packets that exceed the path MTU between the ITR and ETR.It is left to the implementor to decide if the stateless or
stateful mechanism SHOULD be implemented. Both or neither can be
used, since it is a local decision in the ITR regarding how
to deal with MTU issues, and sites can interoperate with differing
mechanisms.Both stateless and stateful mechanisms also apply to
Re-encapsulating and Recursive Tunneling, so any actions
below referring to an ITR also apply to a TE-ITR.An ITR stateless solution to handle MTU issues is described as
follows:Define H to be the size, in octets, of the outer header an ITR
prepends to a packet. This includes the UDP and LISP header lengths.Define L to be the size, in octets, of the maximum-sized packet
an ITR can send to an ETR without the need for the ITR or any
intermediate routers to fragment the packet.Define an architectural constant S for the maximum size of a
packet, in octets, an ITR MUST receive from the source so the
effective MTU can be met. That is, L = S + H.When an ITR receives a packet from a site-facing interface and
adds H octets worth of encapsulation to yield a packet size
greater than L octets (meaning the received packet size was
greater than S octets from the source), it resolves the MTU issue
by first splitting the original packet into 2 equal-sized
fragments. A LISP header is then prepended to each fragment. The
size of the encapsulated fragments is then (S/2 + H), which is
less than the ITR's estimate of the path MTU between the ITR and
its correspondent ETR.When an ETR receives encapsulated fragments, it treats them
as two individually encapsulated packets. It strips the LISP
headers and then forwards each fragment to the destination host of
the destination site. The two fragments are reassembled at
the destination host into the single IP datagram that was
originated by the source host. Note that reassembly can happen
at the ETR if the encapsulated packet was fragmented at or after the
ITR.This behavior is performed by the ITR when the source host
originates a packet with the 'DF' field of the IP header set to 0.
When the 'DF' field of the IP header is set to 1, or the packet is
an IPv6 packet originated by the source host, the ITR will drop
the packet when the size is greater than L and send an ICMP
Unreachable/Fragmentation-Needed message to the source with a
value of S, where S is (L - H).When the outer-header encapsulation uses an IPv4 header, an
implementation SHOULD set the DF bit to 1 so ETR fragment
reassembly can be avoided. An implementation MAY set the DF
bit in such headers to 0 if it has good reason to believe
there are unresolvable path MTU issues between the sending ITR
and the receiving ETR.This specification RECOMMENDS that L be defined as 1500.An ITR stateful solution to handle MTU issues is described as
follows and was first introduced in :The ITR will keep state of the effective MTU for each Locator
per Map-Cache entry. The effective MTU is what the core network
can deliver along the path between the ITR and ETR.When an IPv6-encapsulated packet, or an IPv4-encapsulated
packet with the DF bit set to 1, exceeds what the core network
can deliver, one of the intermediate routers on the path will
send an ICMP Unreachable/Fragmentation-Needed message to the
ITR. The ITR will parse the ICMP message to determine which
Locator is affected by the effective MTU change and then
record the new effective MTU value in the Map-Cache entry.When a packet is received by the ITR from a source inside
of the site and the size of the packet is greater than the
effective MTU stored with the Map-Cache entry associated with
the destination EID the packet is for, the ITR will send an
ICMP Unreachable/Fragmentation-Needed message back to the
source. The packet size advertised by the ITR in the ICMP
Unreachable/Fragmentation-Needed message is the effective MTU
minus the LISP encapsulation length.Even though this mechanism is stateful, it has advantages over
the stateless IP fragmentation mechanism, by not involving the
destination host with reassembly of ITR fragmented packets.There are several cases where segregation is needed at the
EID level. For instance, this is the case for deployments
containing overlapping addresses, traffic isolation policies
or multi-tenant virtualization. For these and other scenarios
where segregation is needed, Instance IDs are used.An Instance ID can be carried in a LISP-encapsulated
packet. An ITR that prepends a LISP header will copy a
24-bit value used by the LISP router to uniquely identify
the address space. The value is copied to the 'Instance ID'
field of the LISP header, and the I-bit is set to 1.When an ETR decapsulates a packet, the Instance ID from the
LISP header is used as a table identifier to locate the
forwarding table to use for the inner destination EID
lookup.For example, an 802.1Q VLAN tag or VPN identifier could be
used as a 24-bit Instance ID. See
for LISP VPN use-case details.The Instance ID that is stored in the mapping database when
LISP-DDT is used is 32 bits
in length. That means the control-plane can store more
instances than a given data-plane can use. Multiple
data-planes can use the same 32-bit space as long as the
low-order 24 bits don't overlap among xTRs.The map-cache contains the state used by ITRs and PITRs to encapsulate packets.
When an ITR/PITR receives a packet from inside the LISP site to a destination
outside of the site a longest-prefix match lookup of the EID is done to the
map-cache (see ). The lookup returns a single Locator-Set
containing a list of RLOCs corresponding to the EID's topological location.
Each RLOC in the Locator-Set is associated with a 'Priority' and 'Weight',
this information is used to select the RLOC to encapsulate.The RLOC with the lowest 'Priority' is selected. An RLOC with 'Priority'
255 means that MUST NOT be used for forwarding. When multiple RLOC have the same
'Priority' then the 'Weight' states how to load balance traffic among them.
The value of the 'Weight' represents the relative weight of the total packets that
match the maping entry.The following are different scenarios for choosing
RLOCs and the controls that are available:The server-side returns one RLOC. The client-side can only
use one RLOC. The server-side has complete control of the
selection.The server-side returns a list of RLOCs where a subset
of the list has the same best Priority. The client can only use
the subset list according to the
weighting assigned by the server-side. In this case, the
server-side controls both the subset list and load-splitting
across its members. The client-side can use RLOCs outside
of the subset list if it determines that the subset
list is unreachable (unless RLOCs are set to a Priority of 255).
Some sharing of control exists: the server-side determines
the destination RLOC list and load distribution while the
client-side has the option of using alternatives to this list if
RLOCs in the list are unreachable.The server-side sets a Weight of zero for the RLOC subset list. In
this case, the client-side can choose how the traffic load is
spread across the subset list. Control is shared by the
server-side determining the list and the client-side determining
load distribution. Again, the client can use alternative RLOCs
if the server-provided list of RLOCs is unreachable.Either side (more likely the server-side ETR)
decides not to send a Map-Request. For example, if the
server-side ETR does not send Map-Requests, it gleans
RLOCs from the client-side ITR, giving the client-side ITR
responsibility for bidirectional RLOC reachability and
preferability. Server-side ETR gleaning of the
client-side ITR RLOC is done by caching the inner-header
source EID and the outer-header source RLOC of received
packets. The client-side ITR controls how traffic is
returned and can alternate using an outer-header source
RLOC, which then can be added to the list the server-side
ETR uses to return traffic. Since no Priority or Weights
are provided using this method, the server-side ETR MUST
assume that each client-side ITR RLOC uses the same best
Priority with a Weight of zero. In addition, since
EID-Prefix encoding cannot be conveyed in data packets,
the EID-to-RLOC Cache on Tunnel Routers can grow to be
very large.Alternatively, RLOC information MAY be gleaned from received tunneled packets or
EID-to-RLOC Map-Request messages. A "gleaned" Map-Cache entry, one learned from the source
RLOC of a received encapsulated packet, is only stored and
used for a few seconds, pending verification. Verification is
performed by sending a Map-Request to the source EID (the
inner-header IP source address) of the received encapsulated
packet. A reply to this "verifying Map-Request" is used to
fully populate the Map-Cache entry for the "gleaned" EID and
is stored and used for the time indicated from the 'TTL' field
of a received Map-Reply. When a verified Map-Cache entry is
stored, data gleaning no longer occurs for subsequent packets
that have a source EID that matches the EID-Prefix of the
verified entry. This "gleaning" mechanism is OPTIONAL, refer to
for security issues regarding this mechanism.RLOCs that appear in EID-to-RLOC Map-Reply messages are
assumed to be reachable when the R-bit for the Locator
record is set to 1. When the R-bit is set to 0, an ITR or
PITR MUST NOT encapsulate to the RLOC. Neither the
information contained in a Map-Reply nor that stored in the
mapping database system provides reachability information
for RLOCs. Note that reachability is not part of the
mapping system and is determined using one or more of the
Routing Locator reachability algorithms described in the
next section.Several data-plane mechanisms for determining RLOC reachability
are currently defined. Please note that additional control-plane
based reachability mechanisms are defined in .An ETR MAY examine the Locator-Status-Bits in the LISP
header of an encapsulated data packet received from an
ITR. If the ETR is also acting as an ITR and has
traffic to return to the original ITR site, it can use
this status information to help select an RLOC.When an ETR receives an encapsulated packet from an ITR,
the source RLOC from the outer header of the packet is likely
up.An ITR/ETR pair can use the 'Echo-Noncing' Locator reachability algorithms
described in this section.When determining Locator up/down reachability by
examining the Locator-Status-Bits from the LISP-encapsulated
data packet, an ETR will receive up-to-date status from an
encapsulating ITR about reachability for all ETRs at the
site. CE-based ITRs at the source site can determine
reachability relative to each other using the site IGP as
follows:Under normal circumstances, each ITR will advertise
a default route into the site IGP.If an ITR fails or if the upstream link to its PE
fails, its default route will either time out or be
withdrawn.Each ITR can thus observe the presence or lack of a
default route originated by the others to determine the
Locator-Status-Bits it sets for them.When ITRs at the site are not deployed in CE routers, the IGP
can still be used to determine the reachability of Locators,
provided they are injected into the IGP. This is
typically done when a /32 address is configured on a loopback
interface. RLOCs listed in a Map-Reply are numbered with ordinals
0 to n-1. The Locator-Status-Bits in a LISP-encapsulated
packet are numbered from 0 to n-1 starting with the least
significant bit. For example, if an RLOC listed in the 3rd
position of the Map-Reply goes down (ordinal value 2),
then all ITRs at the site will clear the 3rd least
significant bit (xxxx x0xx) of the 'Locator-Status-Bits'
field for the packets they encapsulate.When an ETR decapsulates a packet, it will check for
any change in the 'Locator-Status-Bits' field. When a bit
goes from 1 to 0, the ETR, if acting also as an ITR, will
refrain from encapsulating packets to an RLOC that is
indicated as down. It will only resume using that RLOC if
the corresponding Locator-Status-Bit returns to a value of
1. Locator-Status-Bits are associated with a Locator-Set
per EID-Prefix. Therefore, when a Locator becomes
unreachable, the Locator-Status-Bit that corresponds to
that Locator's position in the list returned by the last
Map-Reply will be set to zero for that particular
EID-Prefix. Refer to for security
related issues regarding Locator-Status-Bits.When an ETR decapsulates a packet, it knows that it is
reachable from the encapsulating ITR because that is
how the packet arrived. In most cases, the ETR can also
reach the ITR but cannot assume this to be true, due to the
possibility of path asymmetry. In the presence of
unidirectional traffic flow from an ITR to an ETR, the ITR
SHOULD NOT use the lack of return traffic as an indication
that the ETR is unreachable. Instead, it MUST use an
alternate mechanism to determine reachability.When data flows bidirectionally between Locators from different
sites, a data-plane mechanism called "nonce echoing" can be
used to determine reachability between an ITR and ETR.
When an ITR wants to solicit a nonce echo, it sets the
N- and E-bits and places a 24-bit nonce
in the LISP header of the next encapsulated data packet.When this packet is received by the ETR, the
encapsulated packet is forwarded as normal. When the ETR
next sends a data packet to the ITR, it includes the nonce
received earlier with the N-bit set and E-bit cleared. The
ITR sees this "echoed nonce" and knows that the path to and
from the ETR is up.The ITR will set the E-bit and N-bit for every packet it sends
while in the echo-nonce-request state. The time the ITR waits
to process the echoed nonce before it determines the path
is unreachable is variable and is a choice left for the
implementation.If the ITR is receiving packets from the ETR but does
not see the nonce echoed while being in the echo-nonce-request
state, then the path to the ETR is unreachable. This decision MAY
be overridden by other Locator reachability
algorithms. Once the ITR determines that the path to the ETR is
down, it can switch to another Locator for that
EID-Prefix.Note that "ITR" and "ETR" are
relative terms here. Both devices MUST be implementing
both ITR and ETR functionality for the echo nonce
mechanism to operate.The ITR and ETR MAY both go into the echo-nonce-request
state at the same time. The number of packets sent or the
time during which echo nonce requests are sent is an
implementation-specific setting. However, when an ITR is
in the echo-nonce-request state, it can echo the ETR's nonce
in the next set of packets that it encapsulates and
subsequently continue sending echo-nonce-request
packets.This mechanism does not completely solve the forward
path reachability problem, as traffic may be
unidirectional. That is, the ETR receiving traffic at a
site MAY not be the same device as an ITR that
transmits traffic from that site, or the site-to-site traffic
is unidirectional so there is no ITR returning traffic.The echo-nonce algorithm is bilateral. That is, if one side
sets the E-bit and the other side is not enabled for echo-noncing,
then the echoing of the nonce does not occur and the requesting
side may erroneously consider the Locator unreachable. An ITR
SHOULD only set the E-bit in an encapsulated data packet when it
knows the ETR is enabled for echo-noncing. This is conveyed by
the E-bit in the RLOC-probe Map-Reply message.A site MAY be multihomed using two or more ETRs. The
hosts and infrastructure within a site will be addressed
using one or more EID-Prefixes that are mapped to the RLOCs
of the relevant ETRs in the mapping system. One possible
failure mode is for an ETR to lose reachability to one or
more of the EID-Prefixes within its own site. When this
occurs when the ETR sends Map-Replies, it can clear the
R-bit associated with its own Locator. And when the ETR is
also an ITR, it can clear its Locator-Status-Bit in the
encapsulation data header.It is recognized that there are no simple solutions to
the site partitioning problem because it is hard to know
which part of the EID-Prefix range is partitioned and which
Locators can reach any sub-ranges of the EID-Prefixes. Note
that this is not a new problem introduced by the LISP
architecture. The problem exists today when a multihomed
site uses BGP to advertise its reachability upstream.When an ETR provides an EID-to-RLOC mapping in a
Map-Reply message that is stored in the map-cache of a
requesting ITR, the Locator-Set for the EID-Prefix MAY
contain different Priority and Weight values for each
locator address. When more than one best Priority Locator
exists, the ITR can decide how to load-share traffic against
the corresponding Locators.The following hash algorithm MAY be used by an ITR to
select a Locator for a packet destined to an EID for the
EID-to-RLOC mapping:Either a source and destination address hash or the
traditional 5-tuple hash can be used. The traditional
5-tuple hash includes the source and destination
addresses; source and destination TCP, UDP, or Stream
Control Transmission Protocol (SCTP) port numbers; and the
IP protocol number field or IPv6 next-protocol fields of a
packet that a host originates from within a LISP
site. When a packet is not a TCP, UDP, or SCTP packet, the
source and destination addresses only from the header are
used to compute the hash.Take the hash value and divide it by the number of
Locators stored in the Locator-Set for the EID-to-RLOC
mapping.The remainder will yield a value of 0 to "number of
Locators minus 1". Use the remainder to select the Locator
in the Locator-Set.Note that when a packet is LISP encapsulated, the source
port number in the outer UDP header needs to be
set. Selecting a hashed value allows core routers that are
attached to Link Aggregation Groups (LAGs) to load-split the
encapsulated packets across member links of such
LAGs. Otherwise, core routers would see a single flow, since
packets have a source address of the ITR, for packets that are
originated by different EIDs at the source site. A suggested
setting for the source port number computed by an ITR is a
5-tuple hash function on the inner header, as described above.Many core router implementations use a 5-tuple hash to decide
how to balance packet load across members of a LAG. The 5-tuple
hash includes the source and destination addresses of the packet
and the source and destination ports when the protocol number in
the packet is TCP or UDP. For this reason, UDP encoding is
used for LISP encapsulation.Since the LISP architecture uses a caching scheme to
retrieve and store EID-to-RLOC mappings, the only way an ITR
can get a more up-to-date mapping is to re-request the
mapping. However, the ITRs do not know when the mappings
change, and the ETRs do not keep track of which ITRs
requested its mappings. For scalability reasons, it is
desirable to maintain this approach but need to provide a
way for ETRs to change their mappings and inform the sites
that are currently communicating with the ETR site using
such mappings.This section defines data-plane mechanisms for updating EID-to-RLOC mappings.
Additionally, the Solicit-Map Request (SMR) control-plane updating mechanism is specified in
.When adding a new Locator record in lexicographic order to
the end of a Locator-Set, it is easy to update
mappings. We assume that new mappings will maintain the same
Locator ordering as the old mapping but will just have new
Locators appended to the end of the list. So, some ITRs
can have a new mapping while other ITRs have only an old
mapping that is used until they time out. When an ITR
has only an old mapping but detects bits set in the
Locator-Status-Bits that correspond to Locators beyond the
list it has cached, it simply ignores them. However,
this can only happen for locator addresses that are
lexicographically greater than the locator addresses in
the existing Locator-Set.When a Locator record is inserted in the middle of a
Locator-Set, to maintain lexicographic order, SMR
procedure is used to inform ITRs and
PITRs of the new Locator-Status-Bit mappings.When a Locator record is removed from a Locator-Set, ITRs that
have the mapping cached will not use the removed Locator
because the xTRs will set the Locator-Status-Bit to 0. So, even if
the Locator is in the list, it will not be used. For new
mapping requests, the xTRs can set the Locator AFI to 0
(indicating an unspecified address),
as well as setting the corresponding Locator-Status-Bit to
0. This forces ITRs with old or new mappings to avoid
using the removed Locator.If many changes occur to a mapping over a long period of
time, one will find empty record slots in the middle of the
Locator-Set and new records appended to the Locator-Set. At
some point, it would be useful to compact the Locator-Set so
the Locator-Status-Bit settings can be efficiently packed.We propose here two approaches for Locator-Set compaction:
one operational mechanism (clock sweep) and one protocol mechanisms (Map-Versioning).
Please note that in addition the Solicit-Map Request (specified in )
is a control-plane mechanisms that can be used to update EID-to-RLOC mappings.The clock sweep approach uses planning in advance and
the use of count-down TTLs to time out mappings that have
already been cached. The default setting for an
EID-to-RLOC mapping TTL is 24 hours. So, there is a 24-hour
window to time out old mappings. The following clock sweep
procedure is used:24 hours before a mapping change is to take
effect, a network administrator configures the ETRs at a
site to start the clock sweep window.During the clock sweep window, ETRs continue to send
Map-Reply messages with the current (unchanged) mapping
records. The TTL for these mappings is set to 1 hour.24 hours later, all previous cache entries will have
timed out, and any active cache entries will time out
within 1 hour. During this 1-hour window, the ETRs
continue to send Map-Reply messages with the current
(unchanged) mapping records with the TTL set to 1
minute.At the end of the 1-hour window, the ETRs will send
Map-Reply messages with the new (changed) mapping
records. So, any active caches can get the new mapping
contents right away if not cached, or in 1 minute if they
had the mapping cached. The new mappings are cached with
a TTL equal to the TTL in the Map-Reply.When there is unidirectional packet flow between an ITR and
ETR, and the EID-to-RLOC mappings change on the ETR, it needs to
inform the ITR so encapsulation to a removed Locator can stop
and can instead be started to a new Locator in the
Locator-Set.An ETR, when it sends Map-Reply messages, conveys its
own Map-Version Number. This is known as the Destination
Map-Version Number. ITRs include the Destination
Map-Version Number in packets they encapsulate to the
site. When an ETR decapsulates a packet and detects that the
Destination Map-Version Number is less than the current
version for its mapping, the SMR procedure described in
occurs.An ITR, when it encapsulates packets to ETRs, can convey
its own Map-Version Number. This is known as the Source
Map-Version Number. When an ETR decapsulates a packet and
detects that the Source Map-Version Number is greater than the
last Map-Version Number sent in a Map-Reply from the ITR's site,
the ETR will send a Map-Request to one of the ETRs for the source
site.A Map-Version Number is used as a sequence number per
EID-Prefix, so values that are greater are considered to be
more recent. A value
of 0 for the Source Map-Version Number or the Destination
Map-Version Number conveys no versioning information, and an
ITR does no comparison with previously received Map-Version
Numbers.A Map-Version Number can be included in Map-Register messages
as well. This is a good way for the Map-Server to assure that
all ETRs for a site registering to it will be synchronized
according to Map-Version Number.See for a more detailed analysis
and description of Database Map-Versioning.A multicast group address, as defined in the original Internet
architecture, is an identifier of a grouping of topologically
independent receiver host locations. The address encoding itself
does not determine the location of the receiver(s). The multicast
routing protocol, and the network-based state the protocol creates,
determine where the receivers are located.In the context of LISP, a multicast group address is both an
EID and a Routing Locator. Therefore, no specific semantic or
action needs to be taken for a destination address, as it would
appear in an IP header. Therefore, a group address that
appears in an inner IP header built by a source host will be
used as the destination EID. The outer IP header (the
destination Routing Locator address), prepended by a LISP
router, can use the same group address as the destination
Routing Locator, use a multicast or unicast Routing Locator
obtained from a Mapping System lookup, or use other means to
determine the group address mapping.With respect to the source Routing Locator address, the ITR
prepends its own IP address as the source address of the outer
IP header. Just like it would if the destination EID was a
unicast address. This source Routing Locator address, like any
other Routing Locator address, MUST be globally routable.There are two approaches for LISP-Multicast, one that uses
native multicast routing in the underlay with no support from
the Mapping System and the other that uses only unicast routing
in the underlay with support from the Mapping System. See and , respectively,
for details. Details for LISP-Multicast and interworking with
non-LISP sites are described in and
.LISP is designed to be very "hardware-based forwarding
friendly". A few implementation techniques can be used to
incrementally implement LISP:When a tunnel-encapsulated packet is received by an
ETR, the outer destination address may not be the address
of the router. This makes it challenging for the control
plane to get packets from the hardware. This may be
mitigated by creating special Forwarding Information Base
(FIB) entries for the EID-Prefixes of EIDs served by the
ETR (those for which the router provides an RLOC
translation). These FIB entries are marked with a flag
indicating that control-plane processing SHOULD be
performed. The forwarding logic of testing for particular
IP protocol number values is not necessary. There are a
few proven cases where no changes to existing deployed
hardware were needed to support the LISP data-plane.On an ITR, prepending a new IP header consists of adding
more octets to a MAC rewrite string and prepending the
string as part of the outgoing encapsulation
procedure. Routers that support Generic Routing Encapsulation
(GRE) tunneling or 6to4 tunneling
may already support this
action.A packet's source address or interface the
packet was received on can be used to select VRF
(Virtual Routing/Forwarding). The VRF's routing table
can be used to find EID-to-RLOC mappings.For performance issues related to map-cache management, see
.Security considerations for LISP are discussed in .A complete LISP threat analysis can be found in , in what follows we provide a summary.The optional mechanisms of gleaning is offered to directly obtain
a mapping from the LISP encapsulated packets. Specifically, an xTR
can learn the EID-to-RLOC mapping by inspecting the source RLOC and
source EID of an encapsulated packet, and insert this new mapping
into its map-cache. An off-path attacker can spoof the source EID
address to divert the traffic sent to the victim's spoofed EID. If
the attacker spoofs the source RLOC, it can mount a DoS attack by
redirecting traffic to the spoofed victim's RLOC, potentially
overloading it.The LISP Data-Plane defines several mechanisms to monitor RLOC
data-plane reachability, in this context Locator-Status Bits,
Nonce-Present and Echo-Nonce bits of the LISP encapsulation header
can be manipulated by an attacker to mount a DoS attack. An off-path
attacker able to spoof the RLOC of a victim's xTR can manipulate
such mechanisms to declare a set of RLOCs unreachable. This can be
used also, for instance, to declare only one RLOC reachable with the
aim of overload it.Map-Versioning is a data-plane mechanism used to signal a peering
xTR that a local EID-to-RLOC mapping has been updated, so that the
peering xTR uses LISP Control-Plane signaling message to retrieve a
fresh mapping. This can be used by an attacker to forge the
map-versioning field of a LISP encapsulated header and force an
excessive amount of signaling between xTRs that may overload them.Most of the attack vectors can be mitigated with careful
deployment and configuration, information learned opportunistically
(such as LSB or gleaning) SHOULD be verified with other reachability
mechanisms. In addition, systematic rate-limitation and filtering is
an effective technique to mitigate attacks that aim to overload the
control-plane.Considerations for network management tools exist so the LISP
protocol suite can be operationally managed. These mechanisms can
be found in and .This section provides guidance to the Internet Assigned Numbers
Authority (IANA) regarding registration of values related to this
data-plane LISP specification, in accordance with BCP 26 .The IANA registry has allocated UDP port number 4341 for the
LISP data-plane. IANA has updated the description for UDP port
4341 as follows:Renumbering: Threat or Menace?Endpoints and Endpoint names: A Proposed
Address Family NumbersIANAOpenLISP Implementation ReportAn initial thank you goes to Dave Oran for planting the seeds for
the initial ideas for LISP. His consultation continues to provide
value to the LISP authors.A special and appreciative thank you goes to Noel Chiappa for
providing architectural impetus over the past decades on separation
of location and identity, as well as detailed reviews of the LISP
architecture and documents, coupled with enthusiasm for making LISP
a practical and incremental transition for the Internet.The authors would like to gratefully acknowledge many people who
have contributed discussions and ideas to the making of this
proposal. They include Scott Brim, Andrew Partan, John Zwiebel,
Jason Schiller, Lixia Zhang, Dorian Kim, Peter Schoenmaker, Vijay
Gill, Geoff Huston, David Conrad, Mark Handley, Ron Bonica, Ted
Seely, Mark Townsley, Chris Morrow, Brian Weis, Dave McGrew, Peter
Lothberg, Dave Thaler, Eliot Lear, Shane Amante, Ved Kafle, Olivier
Bonaventure, Luigi Iannone, Robin Whittle, Brian Carpenter, Joel
Halpern, Terry Manderson, Roger Jorgensen, Ran Atkinson, Stig
Venaas, Iljitsch van Beijnum, Roland Bless, Dana Blair, Bill Lynch,
Marc Woolward, Damien Saucez, Damian Lezama, Attilla De Groot,
Parantap Lahiri, David Black, Roque Gagliano, Isidor Kouvelas,
Jesper Skriver, Fred Templin, Margaret Wasserman, Sam Hartman,
Michael Hofling, Pedro Marques, Jari Arkko, Gregg Schudel, Srinivas
Subramanian, Amit Jain, Xu Xiaohu, Dhirendra Trivedi, Yakov Rekhter,
John Scudder, John Drake, Dimitri Papadimitriou, Ross Callon, Selina
Heimlich, Job Snijders, Vina Ermagan, Fabio Maino, Victor Moreno,
Chris White, Clarence Filsfils, Alia Atlas, Florin Coras and Alberto
Rodriguez.This work originated in the Routing Research Group (RRG) of the
IRTF. An individual submission was converted into the IETF LISP
working group document that became this RFC.The LISP working group would like to give a special thanks to
Jari Arkko, the Internet Area AD at the time that the set of LISP
documents were being prepared for IESG last call, and for his
meticulous reviews and detailed commentaries on the 7 working group
last call documents progressing toward standards-track RFCs.[RFC Editor: Please delete this section on publication as RFC.]Posted March 2018.Removed sections 16, 17 and 18 (Mobility, Deployment and Traceroute considerations). This text must be placed in a new OAM document.Posted March 2018.Updated section 'Router Locator Selection' stating that the data-plane MUST follow what's stored in the map-cache (priorities and weights).Section 'Routing Locator Reachability': Removed bullet point 2 (ICMP Network/Host Unreachable),3 (hints from BGP),4 (ICMP Port Unreachable),5 (receive a Map-Reply as a response) and RLOC probing Removed 'Solicit-Map Request'.Posted January 2018.Add more details in section 5.3 about DSCP processing during
encapsulation and decapsulation.Added clarity to definitions in the Definition of Terms section
from various commenters.Removed PA and PI definitions from Definition of Terms section.More editorial changes.Removed 4342 from IANA section and move to RFC6833 IANA section.Posted January 2018.Remove references to research work for any protocol mechanisms.Document scanned to make sure it is RFC 2119 compliant.Made changes to reflect comments from document WG shepherd Luigi
Iannone.Ran IDNITs on the document.Posted November 2017.Rephrase how Instance-IDs are used and don't refer to addresses.Posted October 2017.Put RTR definition before it is used.Rename references that are now working group drafts.Remove "EIDs MUST NOT be used as used by a host to refer to
other hosts. Note that EID blocks MAY LISP RLOCs".Indicate what address-family can appear in data packets.ETRs may, rather than will, be the ones to send Map-Replies.Recommend, rather than mandate, max encapsulation headers to 2.Reference VPN draft when introducing Instance-ID.Indicate that SMRs can be sent when ITR/ETR are in the same node.Clarify when private addreses can be used.Posted August 2017.Make it clear that a Reencapsulating Tunnel Router is an RTR.Posted July 2017.Changed reference of IPv6 RFC2460 to RFC8200.Indicate that the applicability statement for UDP zero checksums
over IPv6 adheres to RFC6936.Posted May 2017.Move the control-plane related codepoints in the IANA Considerations
section to RFC6833bis.Posted April 2017.Reflect some editorial comments from Damien Sausez.Posted March 2017.Include references to new RFCs published.Change references from RFC6833 to RFC6833bis.Clarified LCAF text in the IANA section.Remove references to "experimental".Posted December 2016.Created working group document from draft-farinacci-lisp
-rfc6830-00 individual submission. No other changes made.