Transcript Constraint-based routing

Helsinki University of Technology – Networking Laboratory
Label Switched VPNs –
Scalability and Performance Analysis
Yavor Ivanov
[email protected]
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Outline
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Introduction
Background
Practical setup
Results
Conclusions
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Introduction
Topic
Label Switched VPNs – scalability and performance analysis
Thesis Goal
The scope of this study focuses on several major questions.
• How traffic engineering will affect the VPN performance?
• What is the scalability potential of Layer3 Label Switched VPNs?
• What is the impact of network failure on the VPN performance and
how it can be minimized?
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Background –
Multiprotocol Label Switching
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MPLS technology combines the performance of layer 2 switching with the
flexibility of layer 3 routing.
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Some of its main features include: improved forwarding mechanisms,
introduction of label stack and constraint-based routing.
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Notorious problems like: network scalability, traffic engineering, integrated
recovery and simplified network management are addressed.
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Mechanism: Label edge routers classify the incoming packets and based on
certain criteria assign labels. After this, packets are forwarded along a label
switched path towards the destination. At each hop, Label switch router
makes forwarding decisions just by examining the appended MPLS label.
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MPLS provides ground for Traffic engineering and Virtual private networking
– two concepts with huge significance in the modern networks.
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Background –
MPLS Traffic Engineering
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Provisioning of the limited resources,
improved network utilization and service
differentiation are required to guarantee
desired QoS level in the network.
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TE is an extension to MPLS for selecting the
most efficient paths across an MPLS
network, based on both bandwidth and
administrative rules. It allows optimization of
traffic flows and load balancing for
underutilized paths.
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Path establishment is constraint-based,
allowing parameters like link bandwidth,
current link utilization, resource
requirements, link loads, etc. to be
considered.
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Constraint-based routing is used for path
selection, meaning that traffic flows are
routed across the network based on their
service requirements, flow priority and the
available resources.
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Background –
MPLS Virtual Private Networks
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The term Virtual Private Network has been associated with a private
communication within a company’s network over a public infrastructure.
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L3VPNs - customer sites maintain relationship only with the provider edge
routers. VPN routes are stored and maintained in the PEs, while the core
routers do not have any knowledge of them. Increased network scalability!
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VPN-IPV4 address family - Customer sites can use private addresses,
which does not need to be advertised publicly and are independent of the
addresses used by customers of other service providers
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L2VPNs - Allows networks based on link-layer technology to be
interconnected via an MPLS backbone (huge parts of the provider networks are
based on legacy technology like ATM, Frame Relay or Ethernet). The difference
between L3 and L2 VPNs can be found in the relation between Provider
Edge (PE) and Customer Edge (CE) devices. In layer2 VPNs, the PE is not
a peer of the CE. It does not store the customer routes, but just maps the
incoming layer2 traffic into emulated pseudo wire/LSP.
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Background –
MPLS Virtual Private Networks
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Background –
Protection and Restoration
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Networks are complex entities with large number of devices and underlying
infrastructure
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To minimize the negative effect of failure events, MPLS-TE introduces
variety of mechanism for network protection and restoration
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Path protection – global protection scheme. This is a recovery mechanism
providing 1:1 protection for the primary LSP. The head-end node preestablishes a backup tunnel, which is used only in case of primary LSP
failure. Poor scalability.
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Fast reroute - local protection scheme. Two distinct mechanisms for
protection and restoration – one-to-one backup and facility backup
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In one-to-one protection scheme the PLR node establishes a separate
backup tunnel (called Detour LSP) for each primary LSP it routes.
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Facility backup establishes a single tunnel, called bypass tunnel in order to
guarantee protection for a set of primary LSPs. Relies on the MPLS label
stack to provide local protection against link or node failures. Node and link
protection.
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Background –
Protection and Restoration
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Point of local repair (PLR) - that is the router, which initiates the backup
tunnel in order to protect link or a node.
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Merge Point (MP) - that is the point where backup tunnel ends.
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Next-hop router (NHop) - this is the router that is one hop away from the
PLR.
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Next-next-hop router (NNHop) - it is the node that is two hops ways from
the PLR
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Practical setup
Goals:
• Study the protection scalability of Label switched VPNs.
• What is the effect of the described restoration mechanisms on the
network performance?
• The importance of these questions is growing proportionally to the
adoption speed of MPLS in the core as well as the increasing
demand for highly reliable service from the customers. That’s why
this study was focused on the resiliency technologies and their
application in MPLS VPNs.
Simulations
• Different simulations, in normal state and under failure conditions,
were planed and performed
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Practical setup
Description
• The practical part of the thesis was divided into three simulation
scenarios.
• The first one gives the comparison basis. It models an MPLS
enabled network without any traffic engineering or protection
mechanisms.
• The second simulation implements TE in the core of the network,
• And the last simulation includes protection and restoration
mechanisms.
• Simulation1 and Simulation2 were split each in two Runs. In the first
one the network is in stable condition. In the second one, network
failure was modeled.
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Practical setup
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Results – Simulation1
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The IP convergence time of both
Simulation Runs differs
significantly. In Simulation1_Run1
the average value is 0.00590s,
while for Run2 it is 0.01835s.
Indicates topology changes
In the first scenario, increased
exchange of updates is monitored
in the beginning of the run (until
routing protocol converges)
Different is the situation with the
second scenario where next-hop
updates mark several peaks in
their activity
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Results – Simulation1
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Data from the first simulation shows that VRF size increases proportionally
to number of sites that participate in it. The larger the VPN, the more entries
are included in the VRF table. Can increase the load over the hardware
resources.
VPN signaling traffic - PEs should be fully meshed within a single AS in
order to have a complete view of the transit routes. The number of IBGP
sessions between all PEs can be expressed by following formula:
(n) (n - 1)/2 ,where “n” is the number of PE routers.
This means that if there are 2 routers, only 1 BGP session is needed. If
there are 4 routers, 6 sessions should be established and if there are 20
routers the number of IBGP sessions grows to 190!
To avoid such problems, BGP Route Reflectors were deployed in the
network.
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Results – Simulation2
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After the link failure at 1000s, VPN RED
delay increases from approximately 0.0042
to 0.0058 and remains in this range until
the end of the simulation.
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For Simulation2_Run1 the highest average
number of entries in the table was 109.82
registered at Area2_PE1. Almost double
was the average table size in the second
run: 209.88 entries, which were marked by
Area3_PE4
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LSP Area1_PE3-Area3_PE5 in the first
simulation had average recovery value of
16.678s with a peak reaching 30.011s. The
same LSP in Simulation2_Run2 had
average recovery time of 13.344s and a
peak value of 20.012s.
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Results – Simulation2
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The IP processing delay in the TE enabled network was reduced noticeably.
Traffic was distributed more evenly across the network, which helped to
take off load from some nodes and put it to another. The explicit path
configuration of LSPs helped to balance the underutilized routes and to
achieve more optimal traffic distribution.
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The delay in some VPNs was reduced (VPN PURPLE) - traffic load was
distributed more evenly over the network. This resulted in reduced delay for
some links in favor of others.
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The recovery times for some LSPs improved significantly.
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Results – Simulation3
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The average number of updates
taken from the Area3_PE4 for
Simulation2 was 149.40, with a
peak value reaching 198. Looking
at the same node in Simulation3
could be seen that the average
number of route updates was
reduced to 145.20 and the peak
was 186.
Average duration of the network
convergence was also lowered
from 30.007s to 26.320s in
Simulation3.
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Results – Simulation3
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The modeled failures did not have the negative impact on the network as in
the first scenario and this was expected.
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Considering the scalability potential of these resiliency mechanisms, path
protection scheme lags behind. Reserving resources on an LSP-basis
means too much wasted resources
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Local protection takes care of multiple tunnels flowing over a protected link,
which is much more scalable.
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In some situations, the protection mechanisms might have a negative effect
on the delivered service. Failure impact is minimized thanks to the backup
LSPs, however if traffic is rerouted to a bypass tunnel with some capacity
constraints, some LSPs will be dropped in favor of other (preempted).
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Conclusions
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The network performance was gradually improving through the different
scenarios mainly because of the MPLS TE mechanisms and the
implemented protection schemes.
Expanding the VPN network might cause some scalability concerns due to
the fact that PE nodes should be connected in a full mesh. Solution: Route
Reflectors
Local reroute might not be able to meet the TE requirements, when failure
occurs, which can result in serious loss of quality.
Path protection mechanism is not as fast as the Fast reroute. Simulations
analysis proved that path protection has poor scalability, which is the reason
why it is not widely implemented.
Expanding the network with its VPN service requires support for different
types of equipment and variety of protocols. Interoperability
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Thank you!
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