ISIS Work Group Fangwei. Hu
Internet-Draft Qiang. Wu
Intended status: Standards Track ZTE Corporation
Expires: June 21, 2015 Andrew. Qu
MediaTec
December 18, 2014
ISIS LSP Flooding Optimization
draft-hu-isis-lsp-flooding-optimization-00.txt
Abstract
This proposal introduces a LSP flooding optimization mechanism for
the Non-SPF Calculation-based LSP. The Non-SPF Calculation-based LSP
is forwarded through the interfaces belonging to a distribution tree
rather than all the adjacencies interfaces of the IS. There is no
backward compatibility issue for this solution.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. O Bit Flag . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Distribution Tree for Non-SPF Calculation-based LSP Flooding 4
5. LSP Flooding . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Backward Compatibility Considerations . . . . . . . . . . . . 4
7. Security Considerations . . . . . . . . . . . . . . . . . . . 4
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
10. Normative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
Once acquiring its directly connected neighbors and building up
adjacencies through Hello PDU, the IS (Intermediate System)
originates the LSP (Link States PDU) to describe its link state
information and sends it to the network through all the interfaces
established adjacencies with neighbors. The IS also receives and
stores the LSP from all the other LSPs in the whole network and forms
as LSDB (Link State Database). The IS calculates the best forwarding
path for the destination based on the LSDB and SPF algorithm. When
receiving LSPs from an interface, they will forwards these LSP to
their neighbors through all the other interfaces except the received
interface. As a result, all the ISs in the giving scope have the
same LSDB. We call this procedure as LSP flooding[IS-IS].
Usually, LSP needs to be fragmented before sending, and the Fragment-
ID indicates what fragment number the LSP is. The LSP fragment zero
and some of the Non-zero fragments contain the mandatory information
for SPF computation, we name them as SPF Calculation-based LSP, and
the other Non-zero fragments are named as Non-SPF Calculation-based
LSP, which is not used for the SPF computation. If all the IS have
flooded the Calculation-based LSP in the entire network, we could
establish a distribution tree based on the SPF algorithm and the
information announced by the Calculation-based LSP. The distribution
tree coves all the IS node in the network, and could be used to
forward the Non-SPF Calculation-based LSP, which reduces the number
of Non-SPF Calculation-based LSP, because the IS only forwards the
Non-SPF Calculation-based LSP through the interfaces belonging to the
distribution tree rather than all the interfaces of that IS node.
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2. Terminology
Distribution Tree: is used for Non-SPF calculation-based LSP flooding
in this document.
Non-SPF Calculation-based LSP: some of the non-zero fragment LSPs
which don't contain the neighbor information. The information in
Non-SPF calculation-based LSP usually is the IP reachabilities
information, and is not used for SPF calculation.
SPF Calculation-based LSP: the zero fragment LSPs and the LSPs
containing the neighbor information. SPF calculation-based LSP
carries the vital information for SPF calculation.
3. O Bit Flag
The first reserved bit in the common LSP header(Figure 1) is
redefined as O bit in this document. If O bit is set to 0, the LSP
is SPF Calculation-based LSP, and if set to 1, the LSP is Non-SPF
Calculation-based LSP.
+--------------------------------------------+
|Intra-domain Touting Protocol Discriminator |
+--------------------------------------------+
| Header Length Indicator |
+--------------------------------------------+
| Version/Protocol ID Extension |
+--------------------------------------------+
| ID Length |
+--------------------------------------------+
| O | R | R | PDU Type |
+--------------------------------------------+
| PDU Version |
+--------------------------------------------+
| Reserved |
+--------------------------------------------+
| Maximum Area Addresses |
+--------------------------------------------+
| PDU Specific Fields |
| |
+--------------------------------------------+
| TLV Section |
| |
+--------------------------------------------+
IS-IS common header
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4. Distribution Tree for Non-SPF Calculation-based LSP Flooding
The IS uses distribution tree to flood the Non-SPF Calculation-based
LSP. The IS with maximum system-ID elected as the root for that
distribution tree, and the metric of neighbour announced by the non-
pseudo node is 1. The OL (overload) flag is ignored when calculating
the distribution tree, which ensure that the tree could cover all the
IS node in the network.
5. LSP Flooding
The IS floods LSP based on the distribution tree rather than all the
other interfaces. The details flood procedure is as following:
o When IS originates SPF Calculation-based LSP, it sets the O bit
flag to zero in the common header of LSP, and sends the LSP
through all the interfaces. We should pay attention that the SPF
calculation LSPs are always forwarded through all the interfaces
whether O bit flag is set or not for that LSPs.
o The IS should forwards the self-originated Non-SPF Calculation-
based LSPs (the O bit is set to 1 of the LSP) through the
interfaces belonged to the distribution tree rather than all the
interfaces. The IS forwards the received Non-SPF Calculation-
based LSPs through the interfaces belonged to the distribution
tree, but except the interfaces received that LSPs.
o If the distribution tree is failed and could not forward LSPs, the
IS should forward all the self-originated LSPs besides the Non-SPF
Calculation-based LSP through all the interfaces of the IS, and
forward the received LSPs through all the other interfaces except
the interface received that LSPs.
6. Backward Compatibility Considerations
There is no backward compatibility issue for this solution. The IS
does not support O bit and distribution tree forwarding for Non-SPF
Calculation-based LSP would ignore the O bit when received the LSP
with O bit set, and forward that LSP through all the interfaces
except the interfaces received that LSP.
7. Security Considerations
8. Acknowledgements
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9. IANA Considerations
10. Normative References
[IS-IS] ISO/IEC 10589:2002, Second Edition,, "Intermediate System
to Intermediate System Intra-Domain Routing Exchange
Protocol for use in Conjunction with the Protocol for
Providing the Connectionless-mode Network Service (ISO
8473)", 2002.
Authors' Addresses
Fangwei Hu
ZTE Corporation
No.889 Bibo Rd
Shanghai 201203
China
Phone: +86 21 68897637
Email: hu.fangwei@zte.com.cn
Qiang Wu
ZTE Corporation
No.86 Zijinhua Rd
Nanjing, Jiang Su 210012
China
Email: wu.qiang4@zte.com.cn
Andrew Qu
MediaTec
Email: andrew.qu@mediatek.com
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