Internet DRAFT - draft-cc-isis-flooding-reduction
draft-cc-isis-flooding-reduction
Network Working Group H. Chen
Internet-Draft D. Cheng
Intended status: Standards Track Huawei Technologies
Expires: October 31, 2018 M. Toy
Verizon
Y. Yang
IBM
April 29, 2018
ISIS Flooding Reduction
draft-cc-isis-flooding-reduction-01
Abstract
This document proposes an approach to flood ISIS link state protocol
data units on a topology that is a subgraph of the complete ISIS
topology per underline physical network, so that the amount of
flooding traffic in the network is greatly reduced, and it would
reduce convergence time with a more stable and optimized routing
environment. The approach can be applied to any network topology in
a single ISIS area.
Requirements Language
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].
Status of this Memo
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3
3. Flooding Topology . . . . . . . . . . . . . . . . . . . . . . 4
4. Extensions to ISIS . . . . . . . . . . . . . . . . . . . . . . 6
5. Flooding Behavior . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Nodes Support Flooding Reduction . . . . . . . . . . . . . 7
5.1.1. Receiving an ISIS LSP . . . . . . . . . . . . . . . . 7
5.1.2. Originating an ISIS LSP . . . . . . . . . . . . . . . 8
5.1.3. An Exception Case . . . . . . . . . . . . . . . . . . 8
5.1.4. One More Note . . . . . . . . . . . . . . . . . . . . 9
5.2. Nodes Not Support Flooding Reduction . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . . 10
Appendix A. Algorithms to Build Flooding Topology . . . . . . . . 10
A.1. Algorithms to Build Tree without Considering Flag F . . . 10
A.2. Algorithms to Build Tree Considering Flag F . . . . . . . 12
A.3. Connecting Leaves . . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
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1. Introduction
For some networks such as dense Data Center (DC) networks, the
existing ISIS Link State PDU (LSP) flooding mechanism is not
efficient and may have some issues. The extra LSP flooding consumes
network bandwidth. Processing the extra LSP flooding, including
receiving, buffering and decoding the extra LSPs, wastes memory space
and processor time. This may cause scalability issues and affect the
network convergence negatively.
A flooding reduction method between spines and leaves is proposed in
[I-D.shen-isis-spine-leaf-ext]. The problem on flooding reduction
and an architectural solution are discussed in
[I-D.li-dynamic-flooding]. This document proposes an approach to
flood ISIS LSPs on a topology that is a subgraph of the entire ISIS
topology per underline physical network, so that the amount of
flooding traffic in the network is greatly reduced. The workload for
processing the extra LSP flooding is decreased significantly. This
would improve the scalability and speed up the network convergence,
stable and optimize the routing environment.
The approach proposed is applicable to any network topology in a
single ISIS area. The approach is backward compatible.
2. Problem Statement
ISIS, like other link-state routing protocols, deploys a so-called
reliable flooding mechanism, where a node must transmit a received or
self-originated LSP to all its ISIS interfaces (except the interface
where a LSP is received) in the defined context. While this
mechanism assures each LSP being distributed to every ISIS node in
the relevant routing area or domain, the side-effect is that the
mechanism often causes redundant LSPs in individual network segments
(e.g., on an ISIS point-to-point link or a broadcast subnet), which
in turn forces ISIS nodes to process identical LSPs more than once.
This results waste of ISIS link bandwidth and ISIS nodes' computing
resources, and the delay of ISIS topology convergence.
The problem explained above becomes more serious in ISIS networks
with large number of nodes and links, and in particular, higher
degree of interconnection (e.g., meshed topology, spine-leaf
topology, etc,). In some environment such as in data centers, the
drawback of the existing flooding mechanism has already caused
operational problems, including repeated and waves of flooding
storms, chock of computing resources, slow convergence, oscillating
topology changes, instability of routing environment.
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One example is as shown in Figure 1 (a), where Node 1, Node 2 and
Node 3 are interconnected in a mesh. When Node 1 receives a new or
updated ISIS LSP on its interface I11, it by default would forward to
its interface Il2 and I13 towards Node 2 and Node 3, respectively,
after processing. Node 2 and Node 3 upon reception of the LSP and
after processing, would potentially flood the same LSP over their
respective interface I23 and I32 toward each other, which is
obviously not necessary and at the cost of link bandwidth as well as
both nodes' computing resource.
In example Figure 1 (b), Node 2 and Node 3 both connect to a LAN
where Node 4, Node 5 and Node 6 also connect to. When Node 1
receives a LSP as in (a) and floods it to Node 2 and Node 3
respectively, the two nodes would in turn both (instead of one) flood
to the LAN, which is unnecessary and at the cost of link bandwidth as
well as computing resource of all nodes connected to the LAN.
| |
|I11 |I11
+--o---+ +--o---+
|Node 1| |Node 1|
+-o--o-+ +-o--o-+
I12 / \ I13 / \
/ \ I12/ \I13
I21/ \I31 / \
+----o-+ I32+-o----+ +----o-+ +-o----+
|Node 2|------|Node 3| |Node 2| |Node 3|
+------+I23 +------+ +--o---+ +---o--+
I2L| LAN |I3L
(a) -----o--------o-----o--o-----
I4L| I5L| I6L|
+---o--+ +--o---+ +--o---+
|Node 4| |Node 5| |Node 6|
+------+ +------+ +------+
(b)
Figure 1
3. Flooding Topology
It is a norm that an ISIS node sending a received LSP and self-
originated LSP to all its ISIS interfaces (except that where an LSP
is received), as the reliable-flooding mechanism requires, i.e., any
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ISIS LSP would potentially traverses on each ISIS link in a given
ISIS network topology, sometimes both directions. As demonstrated in
Section 2, dissemination over the entire ISIS network topology has
drawbacks.
To change ISIS's aggressive flooding behavior, a flooding topology is
introduced. For a given ISIS network topology, a flooding topology
is a sub-graph or sub-network of the given network topology that has
the same reachability to every node as the given network topology.
Thus all the nodes in the given network topology MUST be in the
flooding topology. All the nodes MUST be inter-connected directly or
indirectly. As a result, ISIS flooding will in most cases occur only
on the flooding topology, that includes all ISIS nodes but a subset
of ISIS links. Note even the flooding topology is a sub-graph of the
original ISIS topology, any single LSP MUST still be disseminated in
the entire ISIS network.
There are many different flooding topologies for a given ISIS network
topology. A chain connecting all the nodes in the given network
topology is a flooding topology. A circle connecting all the nodes
is another flooding topology. A tree connecting all the nodes is a
flooding topology. In addition, the tree plus the connections
between some leaves of the tree and branch nodes of the tree is a
flooding topology.
There are many different ways to construct a flooding topology for a
given ISIS network topology. A few of them are listed below:
o One node in the network builds a flooding topology and floods the
flooding topology to all the other nodes in the network (This
seems not very good. Flooding the flooding topology may increase
the flooding.);
o Each node in the network automatically calculates a flooding
topology by using the same algorithm (No flooding for flooding
topology);
o Links on the flooding topology are configured statically.
The minimum requirement for a flooding topology is all ISIS nodes are
interconnected (directly or indirectly), but there is only one path
from any node to any other node. While this lean-and-mean type of
flooding topology degrades ISIS flooding traffic volume to the least,
it may introduce some delay of topology convergence in the network
with some network topologies. To compensate convergence efficiency,
additional ISIS links may be added as part of the flooding topology.
There is a trade-off between the density of the flooding topology and
the convergence efficiency.
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Note that the flooding topology constructed by an ISIS node is
dynamic in nature, that means when the ISIS's base topology (the
entire topology graph) changes, the flooding topology (the sub-graph)
MUST be re-computed/re-constructed to ensure that any node that is
reachable on the base topology MUST also be reachable on the flooding
topology.
For reference purpose, some algorithms that allow ISIS nodes to
automatically compute flooding topology are elaborated in Appendix A.
However, this document does not attempt to standardize how a flooding
topology is established.
4. Extensions to ISIS
A 1-bit flag F is defined in an ISIS router capability TLV. Flag F
set to 1 indicates that the router supports ISIS LSP flood reduction
described in this document; and Flag F set to 0 indicates that the
router does not do so.
This flag is used for an ISIS node during the process of computing a
flooding topology. An ISIS node that advertises its LSP containing a
capability TLV with "F" bit set to 1 MUST always be included in the
flooding topology computed by other ISIS nodes; but in contrast, the
node with "F" bit set to zero may or may not be included in the
flooding topology by other nodes, depending on how other nodes
construct their flooding topology.
This flag can also be used for an ISIS node to trigger a decision
whether it wants to perform LSP flooding to its neighbor.
The format of an ISIS router capability TLV with flag F is shown
below.
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 = 242 |Length(5 ~ 255)| Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router ID |Reserved |F|D|S| Optional |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-TLVs ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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5. Flooding Behavior
5.1. Nodes Support Flooding Reduction
This section describes ISIS flooding behavior for ISIS nodes that
support flooding reduction described in this document. For these
nodes, they MUST set "F" bit to 1 in their LSPs (see Section 4). The
flooding behavior for these nodes differs from that as specified in
ISIS ([RFC1195]). Section 5.1.1 describes the flooding behavior when
an ISIS node receives an ISIS LSP from one of its interface, and
Section 5.1.2 describes the flooding behavior for LSP originated by
itself.
The revised flooding procedure MUST flood LSPs to every node in the
network in any case, as the standard ISIS flooding procedure does.
It assumes that the ISIS node of which the flooding behavior is
described below is on the flooding topology, i.e., the node and at
least one of its ISIS interface are on the flooding topology, where:
1. When the node has only one interface on the flooding topology,
the node is a leaf on the topology.
2. When the node has two interfaces on the flooding topology, the
node is a transit node on the topology.
3. A flooding topology with nodes having one or two interfaces on
the topology is a lean graph, i.e., there is only one path from
any node to any other node on the graph. For flooding
efficiency, there could be extra ISIS interfaces that are on the
flooding topology, i.e., a node may have more than two interfaces
that belong to the flooding topology.
5.1.1. Receiving an ISIS LSP
The flooding behavior when an ISIS node receives a newer ISIS LSP
that is not originated by itself from one of its ISIS interface is as
follows:
1. The LSP is received on a link that is on the flooding topology.
The LSP is flooded only to all the other interfaces that are on
the flooding topology.
2. The LSP is received on a link that is not on the flooding
topology. This situation can happen when a neighboring node on a
point-to-point link newly forms adjacency with the receiving
node, or is not currently on the flooding topology; it can happen
when the LSP sending neighbor does not support the ISIS flooding
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reduction (i.e., with "F" bit set to zero); it can also happen as
the receiving link is a broadcast-type interface. The LSP is
flooded only to all other interfaces that are on the flooding
topology.
3. In both cases above, if there is any neighboring node that is
advertising its Router LSP with "F" bit set to zero (see
Section 4) but it is not on the flooding topology, the received
LSP MUST also be sent to this neighboring node.
In any case, the LSP must not be transmitted back to the receiving
interface.
Note before forwarding a received LSP, the ISIS node would do the
normal processing as usual.
5.1.2. Originating an ISIS LSP
The flooding behavior when an ISIS node originates an ISIS LSP is as
follows:
1. If it is a refresh LSP, i.e., there is no significant change
contained in the LSP comparing to the previous LSP, the LSP is
transmitted over links on the flooding topology. In addition, if
there is any neighboring node that is advertising its Router LSP
with "F" bit set to zero (see Section 4) but it is not on the
flooding topology, the LSP MUST also be sent to this neighboring
node.
2. Otherwise, the LSP is transmitted to all ISIS interfaces.
Choosing this action instead of limiting to links on flooding
topology would speed up the synchronization around the
advertising node's neighbors, which could then disseminate the
new LSP quickly.
5.1.3. An Exception Case
In Section 5.1.1 and Section 5.1.2, there are times when an ISIS node
sending out a LSP to an interface on the flooding topology detects a
critical interface or node failure. A critical interface is an
interface on the flooding topology and is the only connection among
some nodes on the flooding topology. When this interface goes down,
the flooding topology will be split. Note the flooding topology was
pre-computed/pre-constructed; but if at the time a critical interface
or a node goes down before a re-newed flooding topology can be
computed/constructed, the ISIS node MUST send out the LSP to all
interfaces (except where it is received from) as a traditional ISIS
node would do. This handling is also taking place if there are more
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than one interfaces or nodes on the existing flooding topology fail,
i.e., if more than one interfaces or nodes on the flooding topology
fail, the ISIS node does traditional flooding before the flooding
topology is re-built.
5.1.4. One More Note
The destination address that is used when an ISIS node sends out a
LSP on an interface on its flooding topology follows the
specification in ISIS ([RFC1195]). This means on a local LAN, all
other ISIS nodes will receive the LSP.
5.2. Nodes Not Support Flooding Reduction
For ISIS nodes that do not support flooding reduction as described in
this document, they MUST set "F" bit to 0 in their Router LSP (see
Section 4); note this is also a default setting. These nodes may or
may not be on the flooding topology constructed by other nodes that
support flooding reduction in the same ISIS area, however that is not
a business these nodes need to concern.
The LSP flooding behavior of ISIS nodes that do not support reduction
as described in this document MUST follow that as specified in ISIS
([RFC1195]).
6. Security Considerations
This document does not introduce any security issue.
7. IANA Considerations
This document has no request to IANA.
8. Acknowledgements
The authors would like to thank Acee Lindem, Zhibo Hu, Robin Li,
Stephane Litkowski and Alvaro Retana for their valuable suggestions
and comments on this draft.
9. References
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9.1. Normative References
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, DOI 10.17487/RFC1195,
December 1990, <https://www.rfc-editor.org/info/rfc1195>.
[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>.
9.2. Informative References
[I-D.li-dynamic-flooding]
Li, T., "Dynamic Flooding on Dense Graphs",
draft-li-dynamic-flooding-04 (work in progress),
March 2018.
[I-D.shen-isis-spine-leaf-ext]
Shen, N., Ginsberg, L., and S. Thyamagundalu, "IS-IS
Routing for Spine-Leaf Topology",
draft-shen-isis-spine-leaf-ext-05 (work in progress),
January 2018.
Appendix A. Algorithms to Build Flooding Topology
There are many algorithms to build a flooding topology. A simple and
efficient one is briefed below.
o Select a node R according to a rule such as the node with the
biggest/smallest node ID;
o Build a tree using R as root of the tree (details below); and then
o Connect k (k>=0) leaves to the tree to have a flooding topology
(details follow).
A.1. Algorithms to Build Tree without Considering Flag F
An algorithm for building a tree from node R as root starts with a
candidate queue Cq containing R and an empty flooding topology Ft:
1. Remove the first node A from Cq and add A into Ft
2. If Cq is empty, then return with Ft
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3. Suppose that node Xi (i = 1, 2, ..., n) is connected to node A
and not in Ft and X1, X2, ..., Xn are in a special order. For
example, X1, X2, ..., Xn are ordered by the cost of the link
between A and Xi. The cost of the link between A and Xi is less
than the cost of the link between A and Xj (j = i + 1). If two
costs are the same, Xi's ID is less than Xj's ID. In another
example, X1, X2, ..., Xn are ordered by their IDs. If they are
not ordered, then make them in the order.
4. Add Xi (i = 1, 2, ..., n) into the end of Cq, goto step 1.
Another algorithm for building a tree from node R as root starts with
a candidate queue Cq containing R and an empty flooding topology Ft:
1. Remove the first node A from Cq and add A into Ft
2. If Cq is empty, then return with Ft
3. Suppose that node Xi (i = 1, 2, ..., n) is connected to node A
and not in Ft and X1, X2, ..., Xn are in a special order. For
example, X1, X2, ..., Xn are ordered by the cost of the link
between A and Xi. The cost of the link between A and Xi is less
than the cost of the link between A and Xj (j = i + 1). If two
costs are the same, Xi's ID is less than Xj's ID. In another
example, X1, X2, ..., Xn are ordered by their IDs. If they are
not ordered, then make them in the order.
4. Add Xi (i = 1, 2, ..., n) into the front of Cq and goto step 1.
A third algorithm for building a tree from node R as root starts with
a candidate list Cq containing R associated with cost 0 and an empty
flooding topology Ft:
1. Remove the first node A from Cq and add A into Ft
2. If all the nodes are on Ft, then return with Ft
3. Suppose that node A is associated with a cost Ca which is the
cost from root R to node A, node Xi (i = 1, 2, ..., n) is
connected to node A and not in Ft and the cost of the link
between A and Xi is LCi (i=1, 2, ..., n). Compute Ci = Ca + LCi,
check if Xi is in Cq and if Cxi (cost from R to Xi) < Ci. If Xi
is not in Cq, then add Xi with cost Ci into Cq; If Xi is in Cq,
then If Cxi > Ci then replace Xi with cost Cxi by Xi with Ci in
Cq; If Cxi == Ci then add Xi with cost Ci into Cq.
4. Make sure Cq is in a special order. Suppose that Ai (i=1, 2,
..., m) are the nodes in Cq, Cai is the cost associated with Ai,
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and IDi is the ID of Ai. One order is that for any k = 1, 2,
..., m-1, Cak < Caj (j = k+1) or Cak = Caj and IDk < IDj. Goto
step 1.
A.2. Algorithms to Build Tree Considering Flag F
An algorithm for building a tree from node R as root with
consideration of flag F starts with a candidate queue Cq containing R
associated with previous hop PH=0 and an empty flooding topology Ft:
1. Remove the first node A with its flag F set to one from the
candidate queue Cq if there is such a node A; otherwise (i.e., if
there is not such node A in Cq), then remove the first node A
from Cq. Add A into the flooding topology Ft.
2. If Cq is empty or all nodes are on Ft, then return with Ft
3. Suppose that node Xi (i = 1, 2, ..., n) is connected to node A
and not in the flooding topology Ft and X1, X2, ..., Xn are in a
special order considering whether some of them with flag F = 1.
For example, X1, X2, ..., Xn are ordered by the cost of the link
between A and Xi. The cost of the link between A and Xi is less
than that of the link between A and Xj (j = i + 1). If two costs
are the same, Xi's ID is less than Xj's ID. The cost of a link
is redefined such that 1) the cost of a link between A and Xi
both with F = 1 is much less than the cost of any link between A
and Xk where Xk with F=0; 2) the real metric of a link between A
and Xi and the real metric of a link between A and Xk are used as
their costs for determining the order of Xi and Xk if they all
(i.e., A, Xi and Xk) with F = 1 or none of Xi and Xk with F = 1.
4. Add Xi (i = 1, 2, ..., n) associated with previous hop PH=A into
the end of the candidate queue Cq, and goto step 1.
Another algorithm for building a tree from node R as root with
consideration of flag F starts with a candidate queue Cq containing R
associated with previous hop PH=0 and an empty flooding topology Ft:
1. Remove the first node A with its flag F set to one from the
candidate queue Cq if there is such a node A; otherwise (i.e., if
there is not such node A in Cq), then remove the first node A
from Cq. Add A into the flooding topology Ft.
2. If Cq is empty or all nodes are on Ft, then return with Ft.
3. Suppose that node Xi (i = 1, 2, ..., n) is connected to node A
and not in the flooding topology Ft and X1, X2, ..., Xn are in a
special order considering whether some of them with F = 1. For
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example, X1, X2, ..., Xn are ordered by the cost of the link
between A and Xi. The cost of the link between A and Xi is less
than the cost of the link between A and Xj (j = i + 1). If two
costs are the same, Xi's ID is less than Xj's ID. The cost of a
link is redefined such that 1) the cost of a link between A and
Xi both with F = 1 is much less than the cost of any link between
A and Xk where Xk with F = 0; 2) the real metric of a link
between A and Xi and the real metric of a link between A and Xk
are used as their costs for determining the order of Xi and Xk if
they all (i.e., A, Xi and Xk) have F = 1 or none of Xi and Xk has
F = 1.
4. Add Xi (i = 1, 2, ..., n) associated with previous hop PH=A into
the front of the candidate queue Cq, and goto step 1.
A third algorithm for building a tree from node R as root with
consideration of flag F starts with a candidate list Cq containing R
associated with low order cost Lc=0, high order cost Hc=0 and
previous hop ID PH=0, and an empty flooding topology Ft:
1. Remove the first node A from Cq and add A into Ft.
2. If all the nodes are on Ft, then return with Ft
3. Suppose that node A is associated with a cost Ca which is the
cost from root R to node A, node Xi (i = 1, 2, ..., n) is
connected to node A and not in Ft and the cost of the link
between A and Xi is LCi (i=1, 2, ..., n). Compute Ci = Ca + LCi,
check if Xi is in Cq and if Cxi (cost from R to Xi) < Ci. If Xi
is not in Cq, then add Xi with cost Ci into Cq; If Xi is in Cq,
then If Cxi > Ci then replace Xi with cost Cxi by Xi with Ci in
Cq; If Cxi == Ci then add Xi with cost Ci into Cq.
4. Suppose that node A is associated with a low order cost LCa which
is the low order cost from root R to node A and a high order cost
HCa which is the high order cost from R to A, node Xi (i = 1, 2,
..., n) is connected to node A and not in the flooding topology
Ft and the real cost of the link between A and Xi is Ci (i=1, 2,
..., n). Compute LCxi and HCxi: LCxi = LCa + Ci if both A and Xi
have flag F set to one, otherwise LCxi = LCa HCxi = HCa + Ci if A
or Xi does not have flag F set to one, otherwise HCxi = HCa If Xi
is not in Cq, then add Xi associated with LCxi, HCxi and PH = A
into Cq; If Xi associated with LCxi' and HCxi' and PHxi' is in
Cq, then If HCxi' > HCxi then replace Xi with HCxi', LCxi' and
PHxi' by Xi with HCxi, LCxi and PH=A in Cq; otherwise (i.e.,
HCxi' == HCxi) if LCxi' > LCxi , then replace Xi with HCxi',
LCxi' and PHxi' by Xi with HCxi, LCxi and PH=A in Cq; otherwise
(i.e., HCxi' == HCxi and LCxi' == LCxi) if PHxi' > PH, then
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replace Xi with HCxi', LCxi' and PHxi' by Xi with HCxi, LCxi and
PH=A in Cq.
5. Make sure Cq is in a special order. Suppose that Ai (i=1, 2,
..., m) are the nodes in Cq, HCai and LCai are low order cost and
high order cost associated with Ai, and IDi is the ID of Ai. One
order is that for any k = 1, 2, ..., m-1, HCak < HCaj (j = k+1)
or HCak = HCaj and LCak < LCaj or HCak = HCaj and LCak = LCaj and
IDk < IDj. Goto step 1.
A.3. Connecting Leaves
Suppose that we have a flooding topology Ft built by one of the
algorithms described above. Ft is like a tree. We may connect k (k
>=0) leaves to the tree to have a enhanced flooding topology with
more connectivity.
Suppose that there are m (0 < m) leaves directly connected to a node
X on the flooding topology Ft. Select k (k <= m) leaves through
using a deterministic algorithm or rule. One algorithm or rule is to
select k leaves that have smaller or larger IDs (i.e., the IDs of
these k leaves are smaller/bigger than the IDs of the other leaves
directly connected to node X). Since every node has a unique ID,
selecting k leaves with smaller or larger IDs is deterministic.
If k = 1, the leaf selected has the smallest/largest node ID among
the IDs of all the leaves directly connected to node X.
For a selected leaf L directly connected to a node N in the flooding
topology Ft, select a connection/adjacency to another node from node
L in Ft through using a deterministic algorithm or rule.
Suppose that leaf node L is directly connected to nodes Ni (i =
1,2,...,s) in the flooding topology Ft via adjacencies and node Ni is
not node N, IDi is the ID of node Ni, and Hi (i = 1,2,...,s) is the
number of hops from node L to node Ni in the flooding topology Ft.
One Algorithm or rule is to select the connection to node Nj (1 <= j
<= s) such that Hj is the largest among H1, H2, ..., Hs. If there is
another node Na ( 1 <= a <= s) and Hj = Ha, then select the one with
smaller (or larger) node ID. That is that if Hj == Ha and IDj < IDa
then select the connection to Nj for selecting the one with smaller
node ID (or if Hj == Ha and IDj < IDa then select the connection to
Na for selecting the one with larger node ID).
Suppose that the number of connections in total between leaves
selected and the nodes in the flooding topology Ft to be added is
NLc. We may have a limit to NLc.
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Authors' Addresses
Huaimo Chen
Huawei Technologies
Email: huaimo.chen@huawei.com
Dean Cheng
Huawei Technologies
Email: dean.cheng@huawei.com
Mehmet Toy
Verizon
USA
Email: mehmet.toy@verizon.com
Yi Yang
IBM
Cary, NC
United States of America
Email: yyietf@gmail.com
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