Internet DRAFT - draft-xie-idr-mpbgp-extension-4map6
draft-xie-idr-mpbgp-extension-4map6
Network Working Group C. Xie
Internet-Draft G. Dong
Intended status: Standards Track China Telecom
Expires: 12 October 2023 X. Li
C. Bao
CERNET Center/Tsinghua University
G. Han
Indirection Network Inc.
10 April 2023
MP-BGP Extension and the Procedures for IPv4/IPv6 Mapping Advertisement
draft-xie-idr-mpbgp-extension-4map6-01
Abstract
This document defines MP-BGP extension and the procedures for IPv4
service delivery in multi-domain IPv6-only underlay networks. It
defines a new BGP path attribute known as the "4map6" in conjunction
with the existing AFI/SAFI in IPv6-only routing paradigm for
transferring IPv4/IPv6 address mapping rule within and across
IPv6-only domains. In addition, the behavior of each type of network
node in this extension is also illustrated.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 12 October 2023.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Terminology and Reference Topology . . . . . . . . . . . . . 3
3. MP-BGP Protocol Extension . . . . . . . . . . . . . . . . . . 5
3.1. NLRI Encoding for Mapping Rule Advertisement . . . . . . 5
3.2. 4map6 BGP Path Attribute . . . . . . . . . . . . . . . . 6
3.3. Explicit Withdrawal of IPv4/IPv6 Mapping Rule . . . . . . 7
4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Advertisement of Mapping Rule Update by egress PE . . . . 8
4.2. Receiving Mapping Rule advertisement by P router . . . . 9
4.3. Receiving Mapping Rule Update by Ingress PE . . . . . . . 10
5. Mapping Rule Capability . . . . . . . . . . . . . . . . . . . 11
6. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 11
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. Security Considerations . . . . . . . . . . . . . . . . . . . 12
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
9.1. Normative References . . . . . . . . . . . . . . . . . . 12
9.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
The document [I-D./draft-ietf-v6ops-framework-md-ipv6only-underlay]
proposes a framework for deploying IPv6-only as the underlay in
multi-domain networks, in which IPv4 packets will be stateless
translated or encapsulated into IPv6 ones for transmission across
IPv6-only underlay domains. To achieve this goal, this framework
introduces a specific data structure called IPv4/IPv6 address mapping
rule to support stateless IPv4-IPv6 packet conversion. For brevity,
in the rest of the document, we will refer to the IPv4/IPv6 address
mapping rule as mapping rule. For an incoming packet, the mapping
rules are used by the ingress PE to generate corresponding IPv6
source and destination addresses from the IPv4 source and destination
address of the original IPv4 packet, and vice versa. Since the
mapping rule for the destination IPv4 address can identify the right
PE egress by providing the IPv6 mapping prefix, it gives the
direction of IPv4 service data transmission throughout the IPv6-only
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network. It is obvious that the exchange of the mapping rule
corresponding to the destination IPv4 address in a packet should
precede to the process of IPv4 data transmission in IPv6-only
network, otherwise, the data originated from IPv4 network will be
dropped due to the absence of the IPv6 mapping prefix corresponding
to its destination address.
When an ingress PE processes the incoming IPv4 packets, the mapping
rule for the source address can be obtained locally, but for the
mapping rule of the destination address, since it is not generated
locally by the ingress PE, it needs corresponding methods to be
obtained remotely. This document defines MP-BGP extension in which
BGP update message contains the mapping rule for IPv4 service
delivery. The extensions include new BGP Path Attribute known as the
"4map6" corresponding to the NLRI and a set of related procedures.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14[RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Terminology and Reference Topology
In the context of this document, multi-domain underlay networks refer
to a network system composed of multiple autonomous systems (i.e.,
AS) interconnected, each AS can serve different scenarios. Multi-
domain networks can be operated by one or more network operators.
Consider the following scenarios, the network shown in figure 1 is
typical multi-domain IPv6-only underlay networks, it is used as a
basic scenario to illustrate the extension of the MP-BGP and its
related procedures in this document. The network comprises of AS1,
AS2 and AS3, it provides IPv4 services communications between IPv4
network 1 and IPv4 network 2, which have IPv4 address block IPv4 A1
and A2 respectively. It is consistent with section 6 of draft [I-
D.ietf-v6ops-framework-md-ipv6only-underlay].
IPv4 A1 +--------+ +-+ +--------+ IPv4 A2
+--------+ / AS1 \ /AS2\ / AS3 \ +--------+
| IPv4 | |+--++ +--+| | |+--+ | | +--+ +-+-+ | | IPv4 |
| network 1|---||PE1|--|P1 |-|--||P2|-|--|-|P3|--|PE2|-|---| network 2|
+--------+ |+---+ +--+| | |+--+ | | +--+ +---+ | +--------+
\___________/ \___/ \___________/
Figure 1.Topology of Typical Multi-domain IPv6-only Networks
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PE and P routers are network routers which constitute the IPv6-only
underlay. The definition of PE and P is consistent with that in
draft [I-D.ietf-v6ops-framework-md-ipv6only-underlay]. It should be
noted that in multi-domain networks, some ASBRs are not at the edge
of the network. In this case, they run as P routers. On each PE
router that the IPv4 address prefix is reachable through, there is a
locally configured IPv6 virtual interface (VIF) address. The VIF
address, as an ordinary global IPv6 /128 address, must also be
injected into the IPv6 IGP so that it is reachable across the multi-
domain transit core.
The following term will be used in this document,
• Distance metric, the distance to the egress PE in terms of the
number of ASes.
The extension of MP-BGP4 for mapping rule processing and transmission
across domains in this draft will involve PE and P routers. Each PE
and P router maintains a Mapping rule Database (MD) as depicted in
figure 2. The entry in the MD database consists of an IPv4 address
prefix, IPv4 address prefix length, IPv6 mapping prefix, IPv6 mapping
prefix length and the distance to the egress. It should be noted
that the database here is just an example, and developers can design
the structure of database according to the actual situation.
+----------+----------------+----------+---------------+------------+
| IPv4 | IPv4 | IPv6 | IPv6 | Distance |
| Address | Address | Mapping | Mapping | to the |
| Prefix | Prefix Length | Prefix | Prefix Length | Egress |
+----------+----------------+----------+---------------+------------+
Figure 2: Entry of Mapping Rule Database
The IPv4 packet sent from IPv4 network 1 will traverse the IPv6-only
network and reach the destination network, i.e., IPv4 network 2. Its
ingress in the IPv6-only network is PE1 and the egress is PE2.
Before the data packet is transmitted, the address mapping rules
corresponding to its IPv4 destination address should be transmitted
from PE2 to PE1. During the mapping rule announcement and
transmission process, it may pass through the intermediate nodes,
such as P3, P2 and P1, and finally reach PE1. For a given
intermediate P node, it may receive advertisement messages of this
mapping rule from multiple upstream intermediate nodes. In order to
reduce the overall quantity of advertisement message, it needs to
select and update the local MD database, generates advertisement
messages based on the selected mapping rule information and transmit
them to downstream intermediate nodes.
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3. MP-BGP Protocol Extension
3.1. NLRI Encoding for Mapping Rule Advertisement
This document specifies a way in which BGP protocol can be used by a
given PE to tell other PE, "If you need to send IPv4 packet whose
destination address is within a given IPv4 address block, please send
them to me, here's the information you need to properly transform the
IPv4 packet into IPv6 one". Multiprotocol BGP (MP-BGP) [RFC4760]
specifies that the set of usable next-hop address families is
determined by the Address Family Identifier (AFI) and the Subsequent
Address Family Identifier (SAFI). [RFC8950] specifies the extensions
to allow advertisement of IPv4 NLRI or VPN IPv4 NLRI with a next-hop
address that belongs to the IPv6 protocol. This document specifies
the extensions necessary to support the transmission of mapping rule
from any egress PE to any ingress PE within and across domains.
Since it is based on IPv6-only routing paradigm, it leverages the
combination of AFI and SAFI, with the value of 2 and 1 respectively,
which identifies Network Layer Reachability Information (NLRI) used
for unicast forwarding in IPv6 network. In addition, in order to
identify that this BGP update message is used for the transmission of
the mapping rule, it needs to contain a newly defined BGP path
attribute type -- the 4map6 attribute. This attribute specifies the
IPv6 mapping prefix that may be used, as well as whatever additional
information (if any) is needed in order to properly transform the
IPv4 packets. The BGP update whose MP_REACH_NLRI attribute contains
the AFI/SAFI combinations and 4map6 BGP path attribute specified
above is called as 4map6 routing information. The use and meaning of
the fields of MP_REACH_NLRI in this case are as follows:
– AFI = 2 (IPv6)
– SAFI = 1 (Unicast)
– Length of Next Hop
– Network Address of Next Hop = When a BGP speaker advertises
the 4map6 NLRI via BGP, it uses its own address as the BGP
next hop in the MP_REACH_NLRI.
– NLRI = Composite IPv6 address prefix, which is composed of
a IPv6 mapping prefix, the original IPv4 address prefix, and
the remaining bits are zero.
The NLRI field is encoded as shown in figure 3:
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+----------------------------+
| Length 1 octet |
+----------------------------+
| Prefix variable |
+----------------------------+
Figure 3: Format of NLRI Field
3.2. 4map6 BGP Path Attribute
As a new BGP path attribute defined in this document, 4map6 attribute
is optional and transitive, it requires IANA to assign a new BGP path
attribute value. The attribute is composed of a set of fields as
below,
+---------------------------------------------------+
| Length of IPv6 Mapping Prefix(1 octet) |
+---------------------------------------------------+
| Forwarding Type(1 octet) |
+---------------------------------------------------+
| Address Origin Type(1 octet) |
+---------------------------------------------------+
| IPv4 Original ASN (4 octets) |
+---------------------------------------------------+
Figure 4:Encoding of the 4map6 attribute
The use and meaning of these fields are as follows:
a) Length of IPv6 Mapping Prefix
This is a 1-octet field whose value expresses the length of IPv6
mapping prefix.
b) Forwarding Type
This field identifies the IPv4/IPv6 forwarding capability of the
egress PE, the data octet can assume the following values:
Value Meaning
0 Translation and encapsulation
1 Encapsulation
2 Translation
c) Address Origin Type
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The data octet can assume the following value:
Value Meaning
0 Local
1 Relay
d) IPv4 Original ASN
This field is the copy of the Origin AS number in BGP update message
received from IPv4 domain.The value of this field exists only when
the value of "Address Origin Type" is 1, otherwise it is NULL.
In addition, when the value of IPv4 Original ASN is set, ATTR_ SET
attribute(type code 128), defined in [RFC 6368], can be used to
transfer the routing information of the IPv4 network in multi-domain
IPv6-only networks.
3.3. Explicit Withdrawal of IPv4/IPv6 Mapping Rule
When a PE ceases to provide egress service for a given IPv4 address
block, it may explicitly withdraw the mapping rules associated with
it. Suppose a PE has announced, on a given BGP session, the mapping
rule of a given IPv4 prefix and it now wishes to withdraw that
mapping rule. To do so, it may send a BGP UPDATE message with an
MP_UNREACH_NLRI attribute.
This encoding of MP_UNREACH_NLRI attribute is used for explicitly
withdrawing the mapping rule for a given IPv4 prefix (on a given BGP
session). Note that IPv4 address prefix/IPv6 mapping prefix bindings
that were not advertised on the given session can not be withdrawn by
this method.
When using an MP_UNREACH_NLRI attribute to withdraw a IPv4 route
whose NLRI was previously specified in an MP_REACH_NLRI attribute,
the lengths and values of the respective prefixes must match, and the
respective AFI/SAFIs must match. An explicit withdrawal in an AFI/
SAFI UPDATE on a given BGP session not only withdraws the binding
between the IPv4 address prefix and the IPv6 mapping prefix, it also
withdraws the path to that prefix that was previously advertised in
an UPDATE on that session.
4. Operation
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4.1. Advertisement of Mapping Rule Update by egress PE
When a PE router learns routing information from the locally attached
IPv4 access networks, the control plane of the PE should process the
information as follows:
1. Install and maintain local IPv4 routing information in the IPv4
routing database.
2. Install and maintain new entries in the MD database. Each entry
should consist of the IPv4 prefix and the local IPv6 mapping prefix.
3. Advertise the new contents of the local MD database in the form
of BGP update advertisement to IPv6 peer routers. The process to
generate IPv6 route advertisement with 4map6 attribute based on IPv4
route advertisement messages is as follows:
a) Set the values of AFI and SAFI in MP_REACH_NLRI to 2 and 1
respectively;
b) The IPv6 mapping prefix of the egress PE splices IPv4 address
blocks in IPv4 routing advertisements to form a composite IPv6
address prefix with the length value denoted by L1. The
composite IPv6 address prefix is copied to address prefix field
of the NLRI structure in the MP_ REACH_NLRI, and the length field
of the NLRI is set to L1, the structure of the composite IPv6
address prefix in NLRI is shown in figure 5. L2 is used to
denote the length of the IPv6 mapping prefix of PE2, i.e.
Pref6-2. When the value of L2 is available, the field of Length
of IPv6 Mapping Prefix in the 4map6 attribute is set to L2.
c) The values of Origin ASN in the original IPv4 route
advertisement is copied to the fields of IPv4 Original ASN of
4map6 attribute, the values of Length of AS_ Path, AS_Path are
copied to the corresponding fields of ATTR_ SET attribute
respectively.
|--------L2--------|
+------------------+------------------+-------------+
| IPv6 Mapping | IPv4 | ...0000... |
| Prefix of PE2 | address prefix | |
+------------------+------------------+-------------+
|-----------------L1------------------|
Figure 5:Structure of IPv6 prefix in NLRI
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4.2. Receiving Mapping Rule advertisement by P router
When a P router receives BGP update advertisement from neighboring P
or PE routers and uses that information to populate the local MD
database, the following procedures are used to update the MD database
and send mapping rule advertisement to next equipment:
1. Validate the received BGP update advertisement as 4map6 routing
information by finding the 4map6 attribute.
2. Extract the IPv4 address prefix which is encoded in positions L2
to L1-1 of the NLRI field and lookup its local MD database, if an
entry which matches the IPv4 address prefix is found, then,
– Compare the distance metric in the 4map6 attribute of BGP
advertisement and that of the entry found, if the former is
less than the latter, then
• Update the entry found in the MD database with the
attributes of BGP advertisement by extracting the IPv6
address prefix from the IPv6 mapping prefix field and
place that as an associated entry next to the IPv4
network index.
• Advertise the updated contents of the local MD database
in the form of MP_REACH_NLRI update information to IPv6
peer routers.
else then
• Keep the entry in the MD database unchanged.
• Advertise the contents of the local MD database in the
form of BGP update advertisement to IPv6 peer routers.
else then
– Install and maintain a new entry in the MD database with
the extracted IPv4 prefix, its corresponding IPv6 mapping
prefix and distance metric to the egress.
– Advertise the contents of the local MD database in the form
of BGP update advertisement to IPv6 peer routers.
It should be noted that this process does not change or affect the
IPv6 FIB table of the P router.
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4.3. Receiving Mapping Rule Update by Ingress PE
When a PE router receives BGP advertisement from neighboring P or PE
routers and uses that information to populate the local MD database
and the BGP routing database, the following procedures are used to
update the MD database and send IPv4 routing information to its IPv4
peers.
1. Validate the received BGP update advertisement as 4map6 routing
information by finding the 4map6 attribute.
2. Extract the IPv6 Mapping Prefix which is encoded in positions 0
to L2-1 of the NLRI field and compare the obtained IPv6 Mapping
Prefix with its own IPv6 Mapping Prefix, and if the two match,
proceed to the next step. Otherwise, this update will be announced
to its other BGP Peers.
3. Extract the IPv4 address prefix which is encoded in positions L2
to L1-1 of the NLRI field and lookup in the MD database, if an entry
which matches the IPv4 address prefix is found, then,
– Compare the distance metric in the BGP advertisement and
that of the entry found, if the former is less than the
latter, then
• Update the entry found in the MD database with the
4map6 attributes of BGP advertisement by extracting the
IPv6 address prefix from the IPv6 mapping prefix field
and place that as an associated entry next to the IPv4
network index
• Redistribute the new 4map6 routing information to the
local IPv4 routing table. Set the destination network
prefix as the extracted IPv4 prefix, set the Next Hop as
Null, and set the OUTPUT Interface as the 4map6 VIF on
the local PE router.
else then
• Keep the entry in the MD unchanged.
else then
– Install and maintain a new entry in the MD database with
the extracted IPv4 prefix, its corresponding IPv6 mapping
prefix and distance metric to the egress.
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– Redistribute the new 4map6 routing information to the local
IPv4 routing table. Set the destination network prefix as
the extracted IPv4 prefix, set the Next Hop as Null, and set
the OUTPUT Interface as the 4map6 VIF on the local PE router.
As mentioned in [I-D./draft-ietf-v6ops-framework-md-ipv6only-
underlay], multi-domain IPv6-only networks support both translation
and encapsulation technologies for IPv4 data delivery at the data
forwarding layer. Take the encapsulation as an example, the
reachability to the egress endpoint of tunnel may change over time,
directly impacting the feasibility of the IPv4 service delivery. A
tunnel that is not feasible at some moment may become feasible at
later time when its egress endpoint address is reachable. The router
may start using the newly feasible tunnel instead of an existing one.
This may happen for translation-based data-path as well. How this
decision is made is outside the scope of this document.
5. Mapping Rule Capability
[RFC5492]defines a Capabilities Optional Parameter and processing
rules. The Capabilities Optional Parameter is a triple that includes
a one-octet Capability Code, a one-octet Capability length, and a
variable-length Capability Value. A BGP speaker can include a
Capabilities Optional Parameter to communicate capabilities in a BGP
OPEN message. A PE or P router that wishes to exchange mapping rule
information must use the Multiprotocol Extensions Capability Code as
defined in [RFC4760], to advertise the corresponding (AFI, SAFI)
pair.
6. Error Handling
When a BGP speaker encounters an error while parsing the 4map6 path
attribute, the speaker must treat the update as a withdrawal of
existing routes to the included 4map6 SAFI NLRIs, or discard the
update if no such routes exist. A log entry should be raised for
local analysis.
7. IANA Considerations
With this document IANA is requested to allocate the following codes,
1)A code for 4map6 path attribute in the BGP “BGP Path Attributes”
registry
2)Value xx for 4map6 in the BGP "Capability Codes" registry
All the codes above use this document as the reference.
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8. Security Considerations
This extension to MP-BGP does not change the underlying security
issues inherent in the existing MP-BGP.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<https://www.rfc-editor.org/info/rfc4760>.
[RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement
with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
2009, <https://www.rfc-editor.org/info/rfc5492>.
[RFC6368] Marques, P., Raszuk, R., Patel, K., Kumaki, K., and T.
Yamagata, "Internal BGP as the Provider/Customer Edge
Protocol for BGP/MPLS IP Virtual Private Networks (VPNs)",
RFC 6368, DOI 10.17487/RFC6368, September 2011,
<https://www.rfc-editor.org/info/rfc6368>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8950] Litkowski, S., Agrawal, S., Ananthamurthy, K., and K.
Patel, "Advertising IPv4 Network Layer Reachability
Information (NLRI) with an IPv6 Next Hop", RFC 8950,
DOI 10.17487/RFC8950, November 2020,
<https://www.rfc-editor.org/info/rfc8950>.
9.2. Informative References
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[I-D.ietf-v6ops-framework-md-ipv6only-underlay]
Xie, C., Ma, C., Li, X., Mishra, G. S., Boucadair, M., and
T. Graf, "Framework of Multi-domain IPv6-only Underlay
Networks and IPv4-as-a-Service", Work in Progress,
Internet-Draft, draft-ietf-v6ops-framework-md-ipv6only-
underlay-01, 3 February 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-v6ops-
framework-md-ipv6only-underlay-01>.
Authors' Addresses
Chongfeng Xie
China Telecom
Beiqijia Town, Changping District
Beijing
102209
China
Email: xiechf@chinatelecom.cn
Guozhen Dong
China Telecom
Beiqijia Town, Changping District
Beijing
102209
China
Email: donggz@chinatelecom.cn
Xing Li
CERNET Center/Tsinghua University
Shuangqing Road No.30, Haidian District
Beijing
100084
China
Email: xing@cernet.edu.cn
Congxiao Bao
CERNET Center/Tsinghua University
Shuangqing Road No.30, Haidian District
Beijing
100084
China
Email: congxiao@cernet.edu.cn
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Guoliang Han
Indirection Network Inc.
Email: guoliang.han@indirectionnet.com
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