Question

question: Draw a MPLS diagram with the following requirements: [ 2 + 8 = 10 marks]

1. 10 IPv6 routers: 4 routers in one segment, 3 routers in second segment, 1 router to connect these two segments

2. Explain MPLS operation in above network.

Answer 1

MPLS Block Diagram

IPv6 Segment Routing

The IPv6 flavor of Segment Routing is implemented using an IPv6 extension header, the Routing Header. The Routing Header (RH) is defined in the IPv6 specifications as a 4-byte header template and contains a Routing Type field, enabling the instantiation of RH subtypes. The IPv6 specifications originally defined RH type 0 (RH0) which provided rudimentary source routing capabilities.

RH0 was later deprecated due to security concerns. The IPv6 Segment Routing Header (SRH) is defined as a new RH of type 4. It contains a list of segments encoded as IPv6 addresses. The SRH may also contain multiple optional Type-Length Values (TLVs). One such TLV is the HMAC TLV, which provides authenticity and integrity checks for the SRH. It addresses security concerns that led to the deprecation of the RH0. In this section, we present the SRH as specified by the version 5 of the IETF draft. At the time of writing, the version 6 has been released. However, the differences between the two versions are mostly technical precisions and synchronisation with other, more recent specifications of principles associated with SRv6.

Segment Routing Header wire format

The first four bytes are part of the generic Routing Header. The Next Header field encodes the type of the header immediately following the SRH (e.g., another extension header, a transport protocol such as TCP or UDP, etc.). The Hdr Ext Len field encodes the length of the SRH as an 8-byte multiple. The Routing Type field is set to 4 [19]. The Segments Left field indicates the number of remaining segments. It is an index into the list of segments subsequently defined. The following four bytes are specific to the SRH. The First Segment field indexes into the list of segments the first segment of the path. The Flags field defines various flags. One such flag is the H-flag which is set to 1 when an HMAC TLV is present. The remaining two bytes are reserved for a future use. Then, the list of segments is encoded as 128-bit IPv6 addresses, in reverse order. The first segment of the list (at index 0) is the last segment of the path. The last segment of the list (indexed by the First Segment field) is the first segment of the path. .