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Motivation

IS-IS Extended TLV draft-shen-isis-extended-tlv-00.txt Naiming Shen (naiming@redback.com) Albert Tian (tian@redback.com). Motivation. IS-IS TLV code space and length is only one byte each the code space will deplete the length max of 255 is an inconvenient restriction

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Motivation

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  1. IS-IS Extended TLVdraft-shen-isis-extended-tlv-00.txt Naiming Shen (naiming@redback.com) Albert Tian (tian@redback.com)

  2. Motivation • IS-IS TLV code space and length is only one byte each • the code space will deplete • the length max of 255 is an inconvenient restriction • IS-IS LSP fragment number of 256 limitation has been recently removed

  3. Extended TLV • Encoding • Type (code 255), an 8 bit field • Length(Lo), an 8 bit field • Length(Hi), an 8 bit field • The length of the Extended TLV is 16 bits by combining Length(Lo) and Length(Hi). The Extended TLV length does not include the Type and Length(Lo) fields. • Extended Type, an 16 bit field • It also inherits the traditional TLV codes ranging 0-254. • Value

  4. Operational Issues • Backwards Compatibility • the Extended TLV can be used in networks even if not all the systems recognize this extension, as long as the usage does not affect the IS-IS routing • the Length(Hi) must be set to zero when used in the backwards compatible mode • IS-IS TLV modes • traditional TLV mode • transitional TLV mode • extended TLV mode

  5. Operational Issues (continue) • Network transition • When start to introduce the IS-IS Extended TLVs, each node can be configured in transitional TLV mode. When a system generates the Extended TLV, it has to also generate its correspondent normal TLV • After all the systems are in transitional mode, they can be converted into extended TLV mode • If none of the system in the network generates the Extended TLV during transition, then they systems can be converted directly into extended TLV mode without the step of transitional TLV mode • Useful to advertise router TLV mode capability

  6. Conclusion • This simple extension defines a backwards compatible way to extend the current IS-IS TLV code and length field from one octet into two octets • TLV code (255) needs to be assigned by IANA • Authors would like to request the adoption as an IS-IS WG document ? • http://www.ietf.org/internet-drafts/drafts-shen-isis-extended-tlv-00.txt

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