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IETF RFC 5642
Dynamic Hostname Exchange Mechanism for OSPF
Last modified on Friday, August 21st, 2009
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Network Working Group S. Venkata
Request for Comments: 5642 Google Inc.
Category: Standards Track S. Harwani
C. Pignataro
Cisco Systems
D. McPherson
Arbor Networks, Inc.
August 2009
Dynamic Hostname Exchange Mechanism for OSPF
 Abstract
This document defines a new OSPF Router Information (RI) TLV that
allows OSPF routers to flood their hostname-to-Router-ID mapping
information across an OSPF network to provide a simple and dynamic
mechanism for routers running OSPF to learn about symbolic hostnames,
just like for routers running IS-IS. This mechanism is applicable to
both OSPFv2 and OSPFv3.
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents in effect on the date of
publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
Venkata, et al. Standards Track PAGE 1 
RFC 5642 Dynamic Hostnames for OSPF August 2009
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Specification of Requirements . . . . . . . . . . . . . . . 3
2. Possible Solutions . . . . . . . . . . . . . . . . . . . . . . 3
3. Implementation . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Dynamic Hostname TLV . . . . . . . . . . . . . . . . . . . 4
3.1.1. Flooding Scope . . . . . . . . . . . . . . . . . . . . 5
3.1.2. Multiple OSPF Instances . . . . . . . . . . . . . . . . 5
4. IPv6 Considerations . . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . . 7
1. Introduction
OSPF uses a 32-bit Router ID to uniquely represent and identify a
node in the network. For management and operational reasons, network
operators need to check the status of OSPF adjacencies, entries in
the routing table, and the content of the OSPF link state database.
When looking at diagnostic information, numerical representations of
Router IDs (e.g., dotted-decimal or hexadecimal representations) are
less clear to humans than symbolic names.
One way to overcome this problem is to define a hostname-to-Router-ID
mapping table on a router. This mapping can be used bidirectionally
(e.g., to find symbolic names for Router IDs and to find Router IDs
for symbolic names) or unidirectionally (e.g., to find symbolic
hostnames for Router IDs). Thus, every router has to maintain a
table with mappings between router names and Router IDs.
These tables need to contain all names and Router IDs of all routers
in the network. If these mapping tables are built by static
definitions, it can currently become a manual and tedious process in
operational networks; modifying these static mapping entries when
additions, deletions, or changes occur becomes a non-scalable process
very prone to error.
This document analyzes possible solutions to this problem (see
Section 2) and provides a way to populate tables by defining a new
Venkata, et al. Standards Track PAGE 2
RFC 5642 Dynamic Hostnames for OSPF August 2009
OSPF Router Information TLV for OSPF, the Dynamic Hostname TLV (see
Section 3). This mechanism is applicable to both OSPFv2 and OSPFv3.
1.1. Specification of Requirements
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 [RFC 2119].
2. Possible Solutions
There are various approaches to providing a name-to-Router-ID mapping
service.
One way to build this table of mappings is by static definitions.
The problem with static definitions is that the network administrator
needs to keep updating the mapping entries manually as the network
changes; this approach does not scale as the network grows, since
there needs to be an entry in the mapping table for each and every
router in the network, on every router in the network. Thus, this
approach greatly suffers from maintainability and scalability
considerations.
Another approach is having a centralized location where the name-to-
Router-ID mapping can be kept. The DNS could be used for this. A
disadvantage with this centralized solution is that it is a single
point of failure; and although enhanced availability of the central
mapping service can be designed, it may not be able to resolve the
hostname in the event of reachability or network problems, which can
be particularly problematic in times of problem resolution. Also,
the response time can be an issue with the centralized solution,
which can be equally problematic. If the DNS is used as the
centralized mapping table, a network operator may desire a different
name mapping than the existing mapping in the DNS, or new routers may
not yet be in the DNS.
Additionally, for OSPFv3 in native IPv6 deployments, the 32-bit
Router ID value will not map to IPv4-addressed entities in the
network, nor will it be DNS resolvable (see Section 4).
The third solution that we have defined in this document is to make
use of the protocol itself to carry the name-to-Router-ID mapping in
a TLV. Routers that understand this TLV can use it to create the
symbolic name-to-Router-ID mapping, and routers that don't understand
it can simply ignore it. This specification provides these semantics
and mapping mechanisms for OSPFv2 and OSPFv3, leveraging the OSPF
Router Information (RI) Link State Advertisement (LSA) ([RFC 4970]).
Venkata, et al. Standards Track PAGE 3
RFC 5642 Dynamic Hostnames for OSPF August 2009
3. Implementation
This extension makes use of the Router Information (RI) Opaque LSA,
defined in [RFC 4970], for both OSPFv2 and OSPFv3, by defining a new
OSPF Router Information (RI) TLV: the Dynamic Hostname TLV.
The Dynamic Hostname TLV (see Section 3.1) is OPTIONAL. Upon receipt
of the TLV, a router may decide to ignore this TLV or to install the
symbolic name and Router ID in its hostname mapping table.
3.1. Dynamic Hostname TLV
The format of the Dynamic Hostname TLV is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hostname ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type Dynamic Hostname TLV Type (7; see Section 6)
Length Total length of the hostname (Value field) in octets, not
including the optional padding.
Value Hostname, a string of 1 to 255 octets, padded with zeroes to
4-octet alignment, encoded in the US-ASCII charset.
Routers that do not recognize the Dynamic Hostname TLV Type ignore
the TLV (see [RFC 4970]).
The Value field identifies the symbolic hostname of the router
originating the LSA. This symbolic name can be the Fully Qualified
Domain Name (FQDN) for the Router ID, it can be a subset of the FQDN,
or it can be any string that operators want to use for the router.
The use of FQDN or a subset of it is strongly recommended since it
can be beneficial to correlate the OSPF dynamic hostname and the DNS
hostname. The format of the DNS hostname is described in [RFC 1035]
and [RFC 2181]. If there is no DNS hostname for the Router ID, if the
Router ID does not map to an IPv4-addressed entity (e.g., see
Section 4), or if an alternate OSPF dynamic hostname naming
convention is desired, any string with significance in the OSPF
routing domain can be used. The string is not null-terminated. The
Router ID of this router is derived from the LSA header, in the
Advertising Router field of the Router Information (RI) Opaque LSA.
Venkata, et al. Standards Track PAGE 4
RFC 5642 Dynamic Hostnames for OSPF August 2009
The Value field is encoded in 7-bit ASCII. If a user-interface for
configuring or displaying this field permits Unicode characters, that
user-interface is responsible for applying the ToASCII and/or
ToUnicode algorithm as described in [RFC 3490] to achieve the correct
format for transmission or display.
The Dynamic Hostname TLV is applicable to both OSPFv2 and OSPFv3.
3.1.1. Flooding Scope
The Dynamic Hostname TLV MAY be advertised within an area-local or
autonomous system (AS)-scope Router Information (RI) LSA. But the
Dynamic Hostname TLV SHOULD NOT be advertised into an area in more
than one RI LSA, irrespective of the scope of the LSA.
In other words, if a router originates a Dynamic Hostname TLV with an
IGP domain (AS) flooding scope, it SHOULD NOT send area-scoped
Dynamic Hostname TLVs except into any attached Not-So-Stubby Area
(NSSA) area(s). Similarly, if a router originates an area-scoped
Dynamic Hostname TLV (other than NSSA area scoped), it SHOULD NOT
send an AS-scoped Dynamic Hostname TLV. When the Dynamic Hostname
TLV is advertised in more than one LSA (e.g., multiple area-scoped
LSAs, or AS-scoped LSAs plus NSSA area-scope LSA(s)), the hostname
SHOULD be the same.
If a router is advertising any AS-scope LSA (other than Dynamic
Hostname TLV RI LSA), such router SHOULD advertise Dynamic Hostname
TLV RI LSA in AS scope. Otherwise, it SHOULD advertise Dynamic
Hostname TLV RI LSA in area scope. For example, an AS boundary
router (ASBR) SHOULD send an AS-scope Dynamic Hostname TLV, whereas
area boundary router (ABRs) and internal routers SHOULD send an area-
scope Dynamic Hostname TLV.
The flooding scope is controlled by the Opaque LSA type in OSPFv2 and
by the S1 and S2 bits in OSPFv3. For area scope, the Dynamic
Hostname TLV MUST be carried within an OSPFv2 Type 10 RI LSA or an
OSPFv3 RI LSA with the S1 bit set and the S2 bit clear. If the
flooding scope is the entire routing domain (AS scope), the Dynamic
Hostname TLV MUST be carried within an OSPFv2 Type 11 RI LSA or
OSPFv3 RI LSA with the S1 bit clear and the S2 bit set.
3.1.2. Multiple OSPF Instances
When an OSPF Router Information (RI) LSA, including the Dynamic
Hostname TLV, is advertised in multiple OSPF instances, the hostname
SHOULD either be preserved or include a common base element. It may
be useful for debugging or other purposes to assign separate
instances different hostnames with a consistent set of suffixes or
Venkata, et al. Standards Track PAGE 5
RFC 5642 Dynamic Hostnames for OSPF August 2009
prefixes that can be associated with a specific instance -- in
particular, when an instance is used for a discrete address family or
non-routing information.
4. IPv6 Considerations
Both OSPFv2 and OSPFv3 employ Router IDs with a common size of 32
bits. In IPv4, the Router ID values were typically derived
automatically from an IPv4 address either configured on a loopback or
physical interface defined on the local system or explicitly defined
within the OSPF process configuration. With broader deployment of
IPv6, it's quite likely that OSPF networks will exist that have no
native IPv4-addressed interfaces. As a result, a 32-bit OSPF Router
ID will need to be either explicitly specified or derived in some
automatic manner that avoids collisions with other OSPF routers
within the local routing domain.
Because this 32-bit value will not map to IPv4-addressed entities in
the network, nor will it be DNS resolvable, it is considered
extremely desirable from an operational perspective that some
mechanism exist to map OSPF Router IDs to more easily interpreted
values -- ideally, human-readable strings. This specification
enables a mapping functionality that eases operational burdens that
may otherwise be introduced with native deployment of IPv6.
5. Security Considerations
Since the hostname-to-Router-ID mapping relies on information
provided by the routers themselves, a misconfigured or compromised
router can inject false mapping information, including a duplicate
hostname for different Router IDs. Thus, this information needs to
be treated with suspicion when, for example, doing diagnostics about
a suspected security incident.
There is potential confusion from name collisions if two routers use
and advertise the same dynamic hostname. Name conflicts are not
crucial, and therefore there is no generic conflict detection or
resolution mechanism in the protocol. However, a router that detects
that a received hostname is the same as the local one can issue a
notification or a management alert.
The use of the FQDN as OSPF dynamic hostname potentially exposes
geographic or other commercial information that can be deduced from
the hostname when sent in the clear. OSPFv3 supports confidentiality
via transport mode IPsec (see [RFC 4552]). OSPFv2 could be operated
over IPsec tunnels if confidentiality is required.
Venkata, et al. Standards Track PAGE 6
RFC 5642 Dynamic Hostnames for OSPF August 2009
This document raises no other new security issues for OSPF. Security
considerations for the base OSPF protocol are covered in [RFC 2328]
and [RFC 5340]. The use of authentication for the OSPF routing
protocols is encouraged.
6. IANA Considerations
IANA maintains the "OSPF Router Information (RI) TLVs" registry
[IANA-RI]. An additional OSPF Router Information TLV Type is defined
in Section 3. It has been assigned by IANA from the Standards Action
allocation range [RFC 4970].
Registry Name: OSPF Router Information (RI) TLVs
Type Value Capabilities Reference
----------- -------------------------------------- ---------
7 OSPF Dynamic Hostname This document
7. Acknowledgments
The authors of this document do not make any claims on the
originality of the ideas described. This document adapts format and
text from similar work done in IS-IS [RFC 5301] (which obsoletes
[RFC 2763]); we would like to thank Naiming Shen and Henk Smit,
authors of [RFC 2763].
The authors would also like to thank Acee Lindem, Abhay Roy, Anton
Smirnov, and Dave Ward for their valuable comments and suggestions.
8. References
8.1. Normative References
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 4970] Lindem, A., Shen, N., Vasseur, JP., Aggarwal, R., and S.
Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 4970, July 2007.
8.2. Informative References
[IANA-RI] Internet Assigned Numbers Authority, "Open Shortest Path
First v2 (OSPFv2) Parameters", <http://www.iana.org>.
[RFC 1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
Venkata, et al. Standards Track PAGE 7
RFC 5642 Dynamic Hostnames for OSPF August 2009
[RFC 2181] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", RFC 2181, July 1997.
[RFC 2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC 2763] Shen, N. and H. Smit, "Dynamic Hostname Exchange Mechanism
for IS-IS", RFC 2763, February 2000.
[RFC 3490] Faltstrom, P., Hoffman, P., and A. Costello,
"Internationalizing Domain Names in Applications (IDNA)",
RFC 3490, March 2003.
[RFC 4552] Gupta, M. and N. Melam, "Authentication/Confidentiality
for OSPFv3", RFC 4552, June 2006.
[RFC 5301] McPherson, D. and N. Shen, "Dynamic Hostname Exchange
Mechanism for IS-IS", RFC 5301, October 2008.
[RFC 5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, July 2008.
Authors' Addresses
Subbaiah Venkata
Google Inc.
EMail: svenkata@google.com
URI: http://www.google.com
Sanjay Harwani
Cisco Systems
EMail: sharwani@cisco.com
URI: http://www.cisco.com
Carlos Pignataro
Cisco Systems
EMail: cpignata@cisco.com
URI: http://www.cisco.com
Danny McPherson
Arbor Networks, Inc.
EMail: danny@arbor.net
Venkata, et al. Standards Track PAGE 8
Dynamic Hostname Exchange Mechanism for OSPF
RFC TOTAL SIZE: 19227 bytes
PUBLICATION DATE: Friday, August 21st, 2009
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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