LSR Working Group A. Wang
Internet-Draft China Telecom
Intended status: Standards Track Z. Hu
Expires: February 27, 2021 Huawei Technologies
August 26, 2020
Passive Interface Attribute
draft-wang-lsr-passive-interface-attribute-01
Abstract
This document describes the mechanism that can be used to
differentiate the passive interfaces from the normal interfaces
within ISIS domain.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 2
3. Scenario Description . . . . . . . . . . . . . . . . . . . . 3
4. Passive Interface Attribute . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
7. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 4
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
Passive interfaces are used commonly within operator or enterprise
networks, especially at the boundary of different IGP domains. Using
passive interface can keep the address that associated with it is
reachable within the domain it belongs to but no other link
information is leaked to the other side in another domain.
For operator which runs different IGP domains that interconnect with
each other, there is desire that to get the inter-as topology
information as that described in
[I-D.ietf-idr-bgpls-inter-as-topology-ext]. If the router that run
BGP-LS within one IGP domain can distinguish the passive
interfaces(also the links between two boundary) from the other normal
interfaces, then it is easy for them to report these link in the
"Stub Link NLRI" via the BGP-LS.
OSPF has the mechanism as described in [RFC2328] to label the passive
interface, but ISIS protocol has no such attribute to label the
passive interface.
This document introduces the mechanism that can be used in such
situation, to label the passive interface via the newly defined
passive interface attribute.
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] .
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3. Scenario Description
Figure 1 illustrates the topology scenario when ISIS/OSPF is running
in different domain. B1, B3 are border routers within IGP domain A,
B2, B4 are border routers within domain B. S1-S4 are the internal
routers within domain A, T1-T4 are the internal routers within domain
B. The two domain are interconnected via the links between B1/B2 and
B3/B4.
Passive interfaces are enabled in the links between B1/B2 and B3/B4
respectively. For domain B, the T1 router that runs OSPF can extract
the passives links from the normal links and report it to IP SDN
controller via the BGP-LS protocol. But for domain A, the S2 router
that runs ISIS can only judge the passive interfaces from other
characteristics, such as no IGP neighbor on this link. Such
judgement can extract these passive links but it is not exactly,
because it covers also the situation when there is some issues to
establish the ISIS adjacency but not the passive interface.
The passive interfaces are also often used in the edge router which
connects the server, for example in the router S1/S4 and T2/T4 in
Figure 1. Knowing these interfaces are correctly configured will
also benefit the management of these interfaces.
The method to label these passive interface explicitly is necessary
then.
+-----------------+
+----+IP SDN Controller+----+
| +-----------------+ |
| |
|BGP-LS |BGP-LS
| |
+---------------+-----+ +-----+--------------+
| +--+ +-++ ++-+ +-++ +|-+ +--+|
| |S1+--------+S2+---+B1+-----------+B2+---+T1+--------+T2||
| +-++ N1 +-++ ++-+ +-++ ++++ N2 +-++|
| | | | | || | |
| | | | | || | |
| +-++ +-++ ++-+ +-++ ++++ +-++|
| |S4+--------+S3+---+B3+-----------+B4+---+T3+--------+T4||
| +--+ +--+ ++-+ +-++ ++-+ +--+|
| | | |
| | | |
| Domain A(ISIS) | | Domain B(OSPF) |
+---------------------+ +--------------------+
Figure 1: Inter-AS Domain Scenarios
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4. Passive Interface Attribute
[RFC7794] defines the "IPv4/IPv6 Extended Reachability Attribute
Flags" sub-TLV to advertise the additional flags associated with a
given prefix advertisement. Currently, only X(Bit 0),R(Bit 1),N(Bit
2), E(Bit 3) flags are defined, here we propose another bit(Bit 4 is
desired) to be assigned by the IANA for the passive interface
attribute, as illustrated in the following Figure2:
0 1 2 3 4 5 6 7...
+-+-+-+-+-+-+-+-+...
|X|R|N|E|P ...
+-+-+-+-+-+-+-+-+...
Figure 2: Prefix Attribute Flags
P-flag: Passive Flag(Bit 4)
Set for local interface that is configured as passive interface.
When the interfaces on one router be configured as the passive
interface, the P-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.
The router receives such advertisement can then easily distinguish
the passive interfaces from the normal interface, and report them to
the SDN controller if it run the BGP-LS protocol.
5. Security Considerations
Security concerns for ISIS are addressed in [RFC5304] and[RFC5310]
Advertisement of the additional information defined in this document
introduces no new security concerns.
6. IANA Considerations
IANA is requested to allocate the P-bit (bit position 4 is desired)
from the "Bit Values for Prefix Attribute Flags Sub-TLV" registry.
7. Acknowledgement
Thanks Shunwan Zhang, Tony Li, Les Ginsberg and Robert Raszuk for
their suggestions and comments on this idea.
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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>.
[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>.
[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-08 (work in progress),
April 2020.
Authors' Addresses
Aijun Wang
China Telecom
Beiqijia Town, Changping District
Beijing 102209
China
Email: wangaj3@chinatelecom.cn
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Zhibo Hu
Huawei Technologies
Huawei Bld., No.156 Beiqing Rd.
Beijing 100095
China
Email: huzhibo@huawei.com
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