The option lettering in the supplied question is malformed. In the standard option order, the source-IP statement is option B, and it is the item that was not added for IS-IS IPv6.

Unlike OSPFv3, IS-IS operates directly over the data-link layer rather than being encapsulated in IPv4 or IPv6. Consequently, an IS-IS Hello PDU does not have an IP header or an IP source address that could be changed to an IPv6 link-local address.

To support IPv6 route processing, IS-IS was extended with the following information:

TLV 232 — IPv6 Interface Address: Carries one or more 128-bit IPv6 interface addresses.

TLV 236 — IPv6 Reachability: Carries IPv6 prefixes, metrics and reachability attributes.

IPv6 NLPID: The value 142 (0x8E) identifies IPv6 as a supported network-layer protocol and is carried when IPv6 reachability is advertised.

Therefore, TLV 232, TLV 236 and the IPv6 NLPID are valid IS-IS IPv6 extensions. Changing an IS-IS Hello packet’s source IP address is not one of them. Huawei IS-IS documentation