Network Working Group D. McPherson
Request for Comments: 5301 Arbor Networks
Obsoletes: 2763 N. Shen
Category: Standards Track Cisco Systems
October 2008 Dynamic Hostname Exchange Mechanism for IS-IS
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.
RFC 2763 defined a simple and dynamic mechanism for routers running
IS-IS to learn about symbolic hostnames. RFC 2763 defined a new TLV
that allows the IS-IS routers to flood their name-to-systemID mapping
information across the IS-IS network.
This document obsoletes RFC 2763. This document moves the capability
provided by RFC 2763 to the Standards Track.
Table of Contents
1. Introduction ....................................................21.1. Specification of Requirements ..............................22. Possible Solutions ..............................................23. Dynamic Hostname TLV ............................................34. Implementation ..................................................45. Security Considerations .........................................46. Acknowledgments .................................................47. IANA Considerations .............................................48. Informative References ..........................................4
IS-IS uses a variable 1-8 byte system ID (normally 6 bytes) to
represent a node in the network. For management and operation
reasons, network operators need to check the status of IS-IS
adjacencies, entries in the routing table, and the content of the
IS-IS link state database. It is obvious that, when looking at
diagnostics information, hexadecimal representations of system IDs
and Link State Protocol Data Unit (LSP) identifiers are less clear
than symbolic names.
One way to overcome this problem is to define a name-to-systemID
mapping on a router. This mapping can be used bidirectionally, e.g.,
to find symbolic names for system IDs and to find system IDs for
symbolic names. One way to build this table of mappings is by static
definitions. Among network administrators who use IS-IS as their
IGP, it is current practice to define such static mappings.
Thus, every router has to maintain a statically-configured table with
mappings between router names and system IDs. These tables need to
contain the names and system IDs of all routers in the network, and
must be modified each time an addition, deletion, or change occurs.
There are several ways one could build such a table. One is via
static configurations. Another scheme that could be implemented is
via DNS lookups. In this document, we provide a third solution,
which in wide-scale implementation and deployment has proven to be
easier and more manageable than static mapping or DNS schemes.
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 [RFC2119].
2. Possible Solutions
The obvious drawback of static configuration of mappings is the issue
of scalability and maintainability. The network operators have to
maintain the name tables. They have to maintain an entry in the
table for every router in the network, on every router in the
network. The effort to create and maintain these static tables grows
with the total number of routers on the network. Changing the name
or system ID of one router, or adding a new router will affect the
configurations of all the other routers on the network. This will
make it very likely that those static tables are outdated.
Having one table that can be updated in a centralized place would be
helpful. One could imagine using the DNS system for this. A
drawback is that during the time of network problems, the response
time of DNS services might not be satisfactory or the DNS services
might not even be available. Another possible drawback might be the
added complexity of DNS. Also, some DNS implementations might not
support A and PTR records for Connection Network Service (CLNS)
Network Service Access Points (NSAPs).
A third way to build dynamic mappings would be to use the transport
mechanism of the routing protocol itself to advertise symbolic names
in IS-IS link-state PDUs. This document defines a new TLV that
allows the IS-IS routers to include the name-to-systemID mapping data
in their LSPs. This will allow simple and reliable transport of name
mapping information across the IS-IS network.
3. Dynamic Hostname TLV
The Dynamic hostname TLV is defined here as TLV type 137.
Length - total length of the value field.
Value - a string of 1 to 255 bytes.
The Dynamic hostname TLV is optional. This TLV may be present in any
fragment of a non-pseudonode LSP. The value field identifies the
symbolic name of the router originating the LSP. This symbolic name
can be the FQDN for the router, it can be a subset of the FQDN, or it
can be any string operators want to use for the router. The use of
FQDN or a subset of it is strongly recommended. The content of this
value is a domain name, see [RFC2181]. The string is not null-
terminated. The system ID of this router can be derived from the LSP
If this TLV is present in a pseudonode LSP, then it SHOULD NOT be
interpreted as the DNS hostname of the router.
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 [RFC3490] to achieve the correct
format for transmission or display.
The Dynamic hostname TLV is optional. When originating an LSP, a
router may decide to include this TLV in its LSP. Upon receipt of an
LSP with the Dynamic hostname TLV, a router may decide to ignore this
TLV, or to install the symbolic name and system ID in its hostname
mapping table for the IS-IS network.
A router may also optionally insert this TLV in its pseudonode LSP
for the association of a symbolic name to a local LAN.
If a system receives a mapping for a name or system ID that is
different from the mapping in the local cache, an implementation
SHOULD replace the existing mapping with the latest information.
5. Security Considerations
Since the name-to-systemID mapping relies on information provided by
the routers themselves, a misconfigured or compromised router can
inject false mapping information. Thus, this information needs to be
treated with suspicion when, for example, doing diagnostics about a
suspected security incident.
This document raises no other new security issues for IS-IS.
Security issues with IS-IS are discussed in [RFC5304].
The original efforts and corresponding acknowledgements provided in
[RFC2763] have enabled this work. In particular, we'd like to
acknowledge Henk Smit as an author of that document.
7. IANA Considerations
This document specifies TLV 137, "Dynamic Name". This TLV has
already been allocated and reserved [RFC2763]. As such, no new
actions are required on the part of IANA.
8. Informative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", RFC 2181, July 1997.
[RFC2763] Shen, N. and H. Smit, "Dynamic Hostname Exchange Mechanism
for IS-IS", RFC 2763, February 2000.
[RFC3490] Faltstrom, P., Hoffman, P., and A. Costello,
"Internationalizing Domain Names in Applications (IDNA)",
RFC 3490, March 2003.
[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, October 2008.
Arbor Networks, Inc.
Cisco Systems, Inc.
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