HCIP-Datacom H12-831_V1.0 Book

All four methods can provide the required return path. R2 and R3 import the IS-IS route 2000::6/128 into OSPFv3, allowing R4’s Echo Request to reach R6. The remaining requirement is a route on Level-1 router R6 for returning the Echo Reply toward R4, because the OSPFv3 routes are not imported back into IS-IS.

The command:

ipv6 default-route-advertise always level-1

unconditionally originates an IPv6 default route in a Level-1 LSP. Configuring it on either R2 or R3 enables R6 to install ::/0 through that router.

The alternative command:

attached-bit advertise always

forces a Level-1-2 router to set the ATT bit in its Level-1 LSP. When Level-1 router R6 receives an LSP with ATT set, it creates a default route toward the advertising Level-1-2 router. Both R2 and R3 are Level-1-2 routers and participate in the OSPFv3 domain, so either can forward R6’s return traffic toward R4.

Thus, either default-route mechanism can be configured on either R2 or R3, making all four options valid. Huawei IS-IS command reference

In OSPFv3, several new LSA types were introduced to support IPv6. The Link-LSA and Intra-Area-Prefix-LSA have the following roles:

✅ Link-LSA is generated per link by each router. It includes:

Link-local IPv6 address

IPv6 prefix(es) associated with the link

Options related to the interface (bitfields)

✅ Intra-Area-Prefix-LSA describes IPv6 prefix information associated with a Router-LSA or a Network-LSA, rather than embedding it directly within them (as in OSPFv2).

❌ A device does not generate an Intra-Area-Prefix-LSA for each link; instead, it generates it per area, and it can contain multiple prefixes.

✅ Official Reference from Huawei:

" In OSPFv3, prefix information is no longer carried in Router-LSAs or Network-LSAs. Instead, Intra-Area-Prefix-LSAs are used to describe prefixes associated with them. "

" Each router generates one Link-LSA per link. The Link-LSA includes the link-local address and the list of IPv6 prefixes for the link. "

— [Huawei HCIA-Datacom Certification Guide – OSPFv3 Chapter]