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IGP Flexible Algorithm with Link LossHuaweiHuawei Bld., No. 156 Beiqing Rd.Beijing100095Chinawangyifan82@huawei.comHuaweiHuawei Bld., No.156 Beiqing Rd.Beijing100095Chinaxuguoqi@huawei.comIGP Flexible Algorithms allow IGPs to compute constraint-based paths.
Since link packet loss rate plays an important role in network evaluation,
links with high packet loss rate should be bypassed during forwarding.
This draft proposes a path computation method based on a maximum link loss constraint to prune unsatisfied links in Flexible Algorithms.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 BCP 14 [RFC2119]
[RFC8174] when, and only when, they appear in all capitals, as shown
here.Link packet loss rate (link loss) is a measure of the percentage of data packets that are lost during transmission over a network.
It is an important performance metric that directly impacts the quality of service, network congestion, security, and overall network efficiency.
Ensuring a low packet loss rate is essential for maintaining efficient and secure network operations.
Consequently, It is necessary to avoid passing through links with a high packet loss rate during forwarding.The link loss is advertised by the Unidirectional Link Loss Sub-TLV defined in by IS-IS and by OSPF,
which describes the loss (as a packet percentage) between two directly connected IS-IS neighbors.
This Sub-TLV is carried in the Application-Specific Link Attributes Sub-TLV advertised by IS-IS or OSPF .IGP Flexible Algorithms allow IGPs to compute constraint-based paths .
Current path computation methods are based on calculating the minimum cost of the path from the source to the destination.
Flex-Algorithm has already supported path computation with the IGP cost, the minimum link delay and the traffic-engineering metric.
defines a family of generic metrics (e.g. bandwidth based metric type) and bandwidth related constraints to support path computation based on bandwidth.
However, current calculation types and metric types cannot support path computation based on link loss,
since the cost of the path should be defined as the maximum/minimum value among all passing links.To overcome the above issue, there are two solutions. First, new
operators like maximum value operator can be defined, which works as
a step function. When the link loss exceeds a threshold, the cost of
the link is set to the maximum. Second, new Flexible Algorithm
Definition (FAD) constraints can be defined to exclude links that do
not meet the link loss requirements during path calculation. The
second method is specifically demonstrated in this draft. The
general ideas are as below. 1. The link loss is used as a link constraint for path computation. That is, the link whose loss rate is greater than the specified value is excluded. 2. Metric-type remains unchanged: igp, te, and delay. With a new FAD constraint Sub-TLV advertised by IGP, links with low packet loss rate will be selected for path computation.
The new Exclude Maximum Link Loss Sub-TLVs are defined in Section 2. The Flex-Algorithm calculation method based on link loss is presented in Section 3.A new Exclude Maximum Link Loss Sub-TLV is defined as a sub-TLV of the FAD TLV. To guarantee loop free forwarding, all routers that participate in a Flex-Algorithm MUST agree on the FAD.
Selected nodes within the IGP domain MUST advertise FADs as described in Sections 5, 6, and 7 of .The Exclude Maximum Link Loss Sub-TLV is proposed to specify the upper limit of the link loss.
When this Sub-TLV is carried in a FAD TLV, all links with packet loss rate larger than the defined maximum link loss value will be excluded from the Flex-Algorithm topology.IS-IS Flex-Algorithm Exclude Maximum Link Loss Sub-TLV (FAEML) is a
sub-TLV of the IS-IS FAD sub-TLV. It has the following format:
The FAEML sub-TLV MUST appear at most once in the FAD Sub-TLV. If it
appears more than once, the IS-IS FAD Sub-TLV MUST be ignored by the
receiver.The maximum link loss advertised in FAEML Sub-TLV MUST be compared
with the link loss advertised in Sub-Sub-TLV 36 of ASLA Sub-
TLV . If L-Flag is set in the ASLA sub-TLV, the maximum link loss
advertised in FAEML sub-TLV MUST be compared with the link loss
advertised by the sub-TLV 36 of the TLV
22/222/23/223/141 as defined in Section 4.2.If the link loss is larger than the maximum link loss advertised in FAEML sub-TLV,
the link MUST be excluded from the Flex-Algorithm topology. If a link does not have the link loss
advertised but the FAD contains the FAEML sub-TLV, then
it MUST NOT be excluded from the Flex-Algorithm topology.OSPF Flex-Algorithm Exclude Maximum Link Loss Sub-TLV (FAEML) is a
sub-TLV of the OSPF FAD sub-TLV. It has the following format:
The FAEML sub-TLV MUST appear at most once in the FAD Sub-TLV. If it
appears more than once, the IS-IS FAD Sub-TLV MUST be ignored by the
receiver.The maximum link loss advertised in FAEML Sub-TLV MUST be compared
with the link loss advertised in Sub-Sub-TLV 30 of ASLA Sub-
TLV . The ASLA Sub-TLV is advertised in Extended Link Opaque LSAs for OSPFv2
and E-Router-LSAs for OSPFv3.If the link loss is larger than the maximum link loss advertised in FAEML sub-TLV,
the link MUST be excluded from the Flex-Algorithm topology. If a link does not have the link loss
advertised but the FAD contains the FAEML sub-TLV, then
it MUST NOT be excluded from the Flex-Algorithm topology.A new rule is added to the rules used to prune links
from the topology during the Flex-Algorithm computation in Section 13 of .1. Check if any exclude FAEML rule is part of the Flex-Algorithm
definition. If such exclude rule exists and the link has link
loss advertised, check if the link satisfies the FAEML rule.
If not, the link MUST be pruned from the computation.Type: 252(TBA)Description: IS-IS Exclude Maximum Link Loss Sub-TLVReference: This document Section 2.1Type: 252(TBA)Description: OSPF Exclude Maximum Link Loss Sub-TLVReference: This document Section 2.2
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