LSR Working Group A. Wang
Internet-Draft China Telecom
Intended status: Standards Track Z. Hu
Expires: April 24, 2021 Huawei Technologies
G. Mishra
Verizon Inc.
October 21, 2020
Passive Interface Attribute
draft-wang-lsr-passive-interface-attribute-05
Abstract
This document describes the mechanism that can be used to
differentiate the passive interfaces from the normal interfaces
within ISIS or OSPF domain.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 3
3. Consideration for flagging passive interface . . . . . . . . 3
4. Prefix Attribute for Passive Interface . . . . . . . . . . . 3
4.1. ISIS Prefix Attribute for Passive Interface . . . . . . . 3
4.2. OSPF Prefix Attribute for Passive Interface . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
Passive interfaces are used commonly within an operators enterprise
or service provider networks. One of the most common use cases for
passive interface is in a data center Layer 2 and Layer 3 TOR(Top of
Rack) switch where the inter connected links between the TOR switches
and uplinks to the Core switch are only a few links and a majority of
the links are Layer 3 VLAN Switched Virtual Interface Default
Gateways trunked between the TOR switches serving Layer 2 broadcast
domains. In this scenario all the VLANs are made passive as it is
recommended to limit the number of network LSAs between routers and
switches to avoid unnecessary hello processing overhead.
Another common use case is an inter-as routing scenario where the
same routing protocol but different IGP instance is running between
the adjacent BGP domains. Using passive interface on the inter-as
tiepoint connections can ensure that prefixes contained within a
domain are only reachable within the domain itself and not allow the
link state database to be merged between domain which could result in
undesirable consequences.
For operator which runs different IGP domains that interconnect with
each other via the passive interfaces, there is desire to obtain the
inter-as topology information as described in
[I-D.ietf-idr-bgpls-inter-as-topology-ext]. If the router that runs
BGP-LS within one IGP domain can distinguish passive interfaces from
other normal interfaces, it is then easy for the router to report
these passive links using BGP-LS to centralized PCE controller.
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On the other hand, passive interfaces are normally the boundary of
one IGP domain, knowing them can facilitate the operators to apply
various policies on such interfaces, for example, to secure their
networks, or filtering the incoming traffic with scrutiny.
But OSPF and ISIS have no position to flag such passive interface
now.
This document defines the protocol extension for OSPF and ISIS to
indicate the prefix that comes from passive interface.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119] .
3. Consideration for flagging passive interface
ISIS [RFC5029] defines the Link-Attributes Sub-TLV to carry the link
attribute information, but this Sub-TLV can only be carried within
the TLV 22, which is used to described the attached neighbor. For
passive interface, there is no ISIS neighbor, then it is not
appropriate to use this Sub-TLV to indicate the passive attribute of
the interface.
OSPFv2[RFC2328] defines link type field within Router LSA, the type 3
for connections to a stub network can be used to identified the
passive interface. But in OSPFv3 [RFC5340], type 3 within the
Router-LSA has been reserved. The information that associated with
stub network has been put in the Intra-Area-Prefix-LSAs.
It is necessary for ISIS and OSPF to extend the protocol to flag the
passive interface then.
4. Prefix Attribute for Passive Interface
Considering there is no IGP neighbor for the passive interface, we
select to define the attribute of the prefix that associated with the
passive interface, similar as the treatment of stub link type in OSPF
v3.
4.1. ISIS Prefix Attribute for Passive Interface
[RFC7794] defines the "IPv4/IPv6 Extended Reachability Attribute
Flags" sub-TLV to advertise the additional flags associated with a
given prefix advertisement. We propose new bit(Bit 5 is desired) to
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be assigned by the IANA for the passive interface attribute, as
illustrated in Figure 2:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|X|R|N|E|A|U| | |
+-+-+-+-+-+-+-+-+
Figure 2: Prefix Attribute Flags
U-flag: Unactive Flag(Bit 5)
Set for local interface that is configured as passive interface.
When the interfaces on one router be configured as passive interface,
the U-flag bit will be set in the "IPv4/IPv6 Extended Reachability
Attribute Flags" sub-TLV. This sub-TLV will be included in the TLV
135, TLV 235, TLV 236 and TLV 237 as necessary and be flooded within
the ISIS domain.
4.2. OSPF Prefix Attribute for Passive Interface
[RFC5340] defines the "Prefix Option field" in "Intra-Area-Prefix-
LSAs" to describe the prefix capabilities. The bits in this field
can be defined to flag the prefix coming from the passive interface.
We propose new bit(Bit 0 is desired) to be assigned by the IANA for
the passive interface, as illustrated in Figure 3:
0 1 2 3 4 5 6 7
+--+--+--+--+--+-+--+--+
| U| E| N|DN| P|x|LA|NU|
+--+--+--+--+--+-+--+--+
Figure 3: The Prefix Options Field
U-flag: Unactive Flag(Bit 0)
Set for local interface that is configured as passive interface.
When the interfaces on one router is configured as passive interface,
the U-flag bit will be set in the "Prefix Option field" of Intra-
Area-Prefix-LSAs.
The router that receives such advertisement can then easily
distinguish the passive interfaces from the normal interface, and
reports them to the PCE controller if it runs the BGP-LS protocol.
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5. Security Considerations
Security concerns for ISIS are addressed in [RFC5304] and[RFC5310]
Security concern for OSPFv3 is addressed in [RFC4552]
Advertisement of the additional information defined in this document
introduces no new security concerns.
6. IANA Considerations
IANA is requested to allocate the U-bit (Bit position 5 is desired)
from the "Bit Values for Prefix Attribute Flags Sub-TLV" registry of
ISIS TLV codepoint.
IANA is requested to allocate the U-bit(Bit position 0 is desired)
from the "OSPFv3 Prefix Options" registry of OSPFv3 Parameters
codepoint.
7. Acknowledgement
Thanks Shunwan Zhang, Tony Li, Les Ginsberg, Acee Lindem, Peter
Psenak, Dhruv Dhody, Jeff Tantsura and Robert Raszuk for their
suggestions and comments on this idea.
8. References
8.1. 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>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>.
[RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality
for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006,
<https://www.rfc-editor.org/info/rfc4552>.
[RFC5029] Vasseur, JP. and S. Previdi, "Definition of an IS-IS Link
Attribute Sub-TLV", RFC 5029, DOI 10.17487/RFC5029,
September 2007, <https://www.rfc-editor.org/info/rfc5029>.
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[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, DOI 10.17487/RFC5304, October
2008, <https://www.rfc-editor.org/info/rfc5304>.
[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic
Authentication", RFC 5310, DOI 10.17487/RFC5310, February
2009, <https://www.rfc-editor.org/info/rfc5310>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<https://www.rfc-editor.org/info/rfc5340>.
[RFC7794] Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and
U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4
and IPv6 Reachability", RFC 7794, DOI 10.17487/RFC7794,
March 2016, <https://www.rfc-editor.org/info/rfc7794>.
8.2. Informative References
[I-D.ietf-idr-bgpls-inter-as-topology-ext]
Wang, A., Chen, H., Talaulikar, K., and S. Zhuang, "BGP-LS
Extension for Inter-AS Topology Retrieval", draft-ietf-
idr-bgpls-inter-as-topology-ext-09 (work in progress),
September 2020.
Authors' Addresses
Aijun Wang
China Telecom
Beiqijia Town, Changping District
Beijing 102209
China
Email: wangaj3@chinatelecom.cn
Zhibo Hu
Huawei Technologies
Huawei Bld., No.156 Beiqing Rd.
Beijing 100095
China
Email: huzhibo@huawei.com
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Gyan S. Mishra
Verizon Inc.
13101 Columbia Pike
Silver Spring MD 20904
United States of America
Email: gyan.s.mishra@verizon.com
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