ITSU3009 Project Part A: Study of Segment Routing in Networking

This report provides an overview of segment routing, a scalable source routing method used in modern networking as an alternative to MPLS. It discusses the working procedure of segment routing, highlighting its ability to control forwarding paths through network instructions without needing additional protocols. The report analyzes two examples to illustrate the practical application of segment routing, emphasizing its benefits such as increased network flexibility, reduced costs, and seamless deployment in IPv6 or MPLS data planes. It also touches on the technology's coexistence with existing LDP networks and its extensive use in contemporary networking environments. Desklib offers this document, along with numerous other resources, to aid students in their studies.

SEGMENT ROUTING
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INTRODUCTION
In the following report, the topic of segment
routing has been evaluated and discussed. The report
discusses a brief introduction about the technology and how
the technology works with relevant diagrams. Two
examples of the technology has been analyzed and
discussed. This new technology can provide extra benefits
to the existing technologies like IP and MPLS networks. It
will also enable the network to become more scalable and
operational by allowing any topology to have FRR
protection. It can also provide quicker interactions with
applications for SDN services in the future. The report
briefly discusses the emerging trends that are occurring on
the field of networking.
DISCUSSION
Segment Routing
A scalable and flexible process of doing source
routing is segment routing. A path is chosen by the source
and it is encoded in a packet header like an ordered
segmented list. For identifying an instruction type, segment
are used. SID or Segment ID is used to identify each
segment which consists of unsigned flat integer containing
32 bits. Maintaining a flow state and application state is no
longer needed for the network due to segment routing. The
segment routing follows the forwarding instructions that is
available in the packet [1]. It relies heavily on the protocols
that are available in OPSF or Open Shortest Path First and
IS-IS or Cisco Intermediate System-to-Intermediate
System. It integrates with MPLS’s multi server rich
capabilities and can work with Multiprotocol Label
Switching or MPLS. It can also work with EVPN, VPLS,
VPWS and L3VPN. By not changing the forward plane, it
can be directly applied to the architecture of MPLS or
Multi-Protocol Label Switching [5]. The network
bandwidth is used more by Segment Routing than the
normal MPLS network with the added advantage of low
latency. With the help of a routing extension header,
segment routing can also be applied with the architecture of
IPv6.
Working procedure of Segment Routing
Any path can be chosen by the router in segment
routing to forward traffic. The path can be IGP (Interior
Gateway Protocol) path or explicit in nature. The segment
routing process helps to create sub paths that is utilized by
the router to combine and create a complete pathway to the
destination of the network. Using new extensions of IGP, a
segment identifier is distributed along the network to
identify a particular segment. It can be applied to IPv6 as
well as IPv4 control planes [6]. The routers that are present
in segment routing does not need Resource Reservation
Protocol or LDP (Label Distribution Protocol) for
allocating the segment identifiers to move their program
forward.
A segment identifier is associated with each link
and router. As per the IGP, the node (router) segment shows
the shortest route to the router and is globally unique. A
node ID is allocated by the network administrator to every
router from another block. But the adjacency segment ID
(link) shows the specific adjacency to a particular router
and is significant locally. The adjacency identifiers are
generated automatically by the routers outside the node
ID’s reserved block [7]. The MPLS stack entry is encoded
as a segment identifier in the MPLS network. The data is
directed thorough a specified path with the help of Segment
IDs.
Segment routing normally uses label switching just
like MPLS but does not use any protocols.
Two types of segment IDs are present. The first
one is Prefix SID. In this segment, the IGP calculates the
prefix of the IP address and is globally unique. The second
one is Adjacency SID which contains the adjacency of a
router to a prospective neighbour. It is locally unique.
Figure 1: Shortest path used by the nodal segment to get to
the related node
(Source: [7])
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The same metric is present in all the links.
Segments are automatically built by OPSF or ISIS where
the shortest path is used by the nodal segment to get to the
related node. It is just one hop for the adjacency segment by
going through the related interface [8]. In the figure, the
global address is advertised by each node with the
associated loop back address. The nodal segment is
installed by the other nodes in the data plane of the segment
routing. In Figure 1, 70 is advertised by B. 70 is used by R
and S to reach B. A local segment 10000 is allocated by F
for the link B-F. It is then advertised in the adjacency
segment where in the data plane, B installs it.
A segment routing block namely (n, m) is
allocated by the operator who then further allocated it to
other blocks through a global SR node. Each node
automatically allocates the adjacency segment which is
present outside the SR block [4]. This is how the shortest
path is reached when the nodal segment is joined with a
prefix.
Relevant examples
Two examples are written as follows:-
Figure 2: First example of Source Routing
(Source: [7])
The segment 70 is advertised to the other nosed by
Node R. For Node S to reach Node R, the segment 70
needs to be used which is also known as source routing.
The ECMP behavior is inherited by the path where A as
well as C will swap their segment 70 with 70. Nodes B and
D will pop the PHP label and send the packet to the R
destination [3].
Figure 3: Second example of Source Routing
(Source: [7])
The traffic can be sent through a specific segment
with the help of an adjacency segment. If Node S wants to
reach Node R, the source path {71, 10000, 70} can be
utilized. Node B can direct the traffic coming from Node A
through the adjacent segment 10000 to Node D and utilize
the IGP path for reaching the destination [2].
CONCLUSION
To conclude the report, it can be stated that
Segment routing is an efficient alternative to the age old
technology MPLS. With the help of network instructions, it
helps to provide control over the forwarding path.
Moreover, it does not need any additional protocols.
Sometimes, it simplifies the network by removing
unnecessary protocols. It does not require path signaling,
thus enabling more network flexibility at a reduced cost.
The deployment of the segment routing procedure is
seamless. It can run automatically in an IPv6 or MPLS data
plane. It has the added advantage of coexisting with the
existing technology of LDP Network. Segment routing is
used extensively in networking nowadays.
REFERENCES
[1]"The Segment Routing Architecture - IEEE Conference
Publication", Ieeexplore.ieee.org, 2018. [Online].
Available:
http://ieeexplore.ieee.org/abstract/document/7417124/.
[Accessed: 31- Mar- 2018].
[2]"Optimized network traffic engineering using segment
routing - IEEE Conference
Publication", Ieeexplore.ieee.org, 2018. [Online].
Available:
http://ieeexplore.ieee.org/abstract/document/7218434/.
[Accessed: 31- Mar- 2018].
[3]"Traffic Engineering with Segment Routing: SDN-Based
Architectural Design and Open Source Implementation -
IEEE Conference Publication", Ieeexplore.ieee.org, 2018.
[Online]. Available:
http://ieeexplore.ieee.org/abstract/document/7313628/.
[Accessed: 31- Mar- 2018].
[4]"Segment Routing", Segment Routing, 2018. [Online].
Available: http://www.segment-routing.net/. [Accessed: 31-
Mar- 2018].
[5]Segment Routing. Cisco Systems, 2016.
[6]"Evolve carrier ethernet architecture with SDN and
segment routing - IEEE Conference
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Publication", Ieeexplore.ieee.org, 2018. [Online].
Available:
http://ieeexplore.ieee.org/abstract/document/6918980/.
[Accessed: 31- Mar- 2018].
[7]"Efficient label encoding in segment-routing enabled
optical networks - IEEE Conference
Publication", Ieeexplore.ieee.org, 2018. [Online].
Available:
http://ieeexplore.ieee.org/abstract/document/7127270/.
[Accessed: 31- Mar- 2018].
[8]"Segment Routing Use Cases - IMDEA Networks
Institute Publications
Repository", Eprints.networks.imdea.org, 2018. [Online].
Available: http://eprints.networks.imdea.org/631/.
[Accessed: 31- Mar- 2018].
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