TAILIEUCHUNG - The Complete IS-IS Routing Protocol- P38

The Complete IS-IS Routing Protocol- P38: IS-IS has always been my favourite Interior Gateway Protocol. Its elegant simplicity, its well-structured data formats, its flexibility and easy extensibility are all appealing – IS-IS epitomizes link-state routing. Whether for this reason or others, IS-IS is the IGP of choice in some of the world’s largest networks. | 370 13. IS-IS Extensions Tcpdump output 23 55 OSI IS-IS length 97 L1 Lan IIH hlen 27 v 1 pdu-v 1 sys-id-len 6 0 max-area 3 0 source-id holding time 40s Flags Level 1 Level 2 lan-id Priority 64 PDU length 97 Protocols supported TLV 129 length 2 NLPID s IPv4 0xcc IPv6 0x8e . Restart Signaling TLV 211 length 3 Flags none Remaining holding time 0s Checksum TLV 12 length 2 checksum 0x0000 unverified Authentication TLV 10 length 17 HMAC-MD5 password 887d36216cc6b0c842b1b25a1b11880d It is the authors opinion that the Checksum TLV should be present per default in IIHs and SNPs if no authentication or simple text authentication is configured. Users should not need to configure it as they do now. It should be rather a default option of the router OS. Once HMAC-MD5 authentication is configured for SNPs and IIHs the Checksum TLV 12 should be omitted entirely because the 128-bit MD5 checksum is much stronger than the Fletcher checksum. Unfortunately not all IS-IS implementations follow the open spirit of ISO 10589 where an unknown TLV is silently ignored. Those implementations tend to log error messages about the unknown TLV and refuse to take adjacencies up which left the implementers with not many choices and causes contemporary IS-IS implementation to be as gentle as possible with introduction of new TLVs. IS-IS is ignorant of the Network Layer prefixes that it transports. RFC 1195 defined a set of TLVs that are used to carry IPv4 Prefixes. Similarly IS-IS needs a set of TLVs for carrying IPv6 related information. These are discussed in the next section. IPv6 Extensions The most important TLV for multi-protocol operation is the Protocols Supported TLV 129 illustrated in Figure . The Protocols Supported TLV 129 lists all the protocols Figure . The Protocols Supported TLV 129 lists all protocols that the router supports IPv6 Extensions 371 that an individual router supports. This TLV is found both in IIHs and LSPs. .

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