Selected Answer: C I would pick C, since both IPV4 and IPV6 share the exact same topology. No need for multipology or transition mode: https://www.ws.afnog.org/afnog2011/are/ipv6-presentations/4-isis-for-ipv6.pdf

Selected Answer: C I think C. Topologies match exact, so no need for multitopology.

The key point here is that it says there is a currently deployed IPV4 network. Once you configure IPv6 on an interface that is already running IPv4, you break the requirement that says "all interfaces on which IS-IS is configured must support the identical set of network address families." There is also a requirement that says "all routers in the IS-IS area (for Level 1 routing) or domain (for Level 2 routing) must support the identical set of network layer address families." I don't have the ability to lab this right now, however I would be interested to see if you had a network running single topology IPv4 only, and then started configuring IPv6 on the interfaces, would it break anything. I would question whether C is correct or not. https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_isis/configuration/xe-3s/irs-xe-3s-book/ip6-route-mult-isis-xe.html#GUID-EA369F57-430A-4F30-B467-4529140CB0B6

Again, i agree with you certstudent2016. At some point in the configuration we have to introduce IPv6 to an already running and converged IPv4 IS-IS single topology. Single topology requires a single address family. ==> this brings adjacencies down The solution is to go MULTITOPOLOGY as MT doesnt care about Address Families. Then you have to have transition feature enabled because of the EXACT SAME TOPOLOGY part of the question. later when you have multitopology and ipv4 and ipv6 then you disable transition feature.

Selected Answer: C C. single topology without enabling transition feature In a single topology design, both IPv4 and IPv6 addresses can be carried inside the same IS-IS domain without building separate topologies. IS-IS, as a Layer 2 protocol, can natively support both IPv4 and IPv6. By using a single topology design without any transition feature, the engineer can enable IPv6 on the existing IPv4 IS-IS network with the same router levels for each protocol per interface, while still keeping one integrated topology.

Selected Answer: D The answer is 100% D

Selected Answer: B https://www.ws.afnog.org/afnog2011/are/ipv6-presentations/4-isis-for-ipv6.pdf toward the ends its given answer - B is correct https://datatracker.ietf.org/doc/rfc5120/

Selected Answer: C I agree with C.

yes it would break adjanency when address familty is different during transition, according to cisco doc: For single-topology IS-IS IPv6, routers must be configured to run the same set of address families. IS-IS performs consistency checks on hello packets and will reject hello packets that do not have the same set of configured address families. For example, a router running IS-IS for both IPv4 and IPv6 will not form an adjacency with a router running IS-IS for IPv4 or IPv6 only. In order to allow adjacency to be formed in mismatched address-families network, the adjacency-check command in IPv6 address family configuration mode must be disabled. https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_isis/configuration/xe-3s/irs-xe-3s-book/ip6-route-isis-xe.html#GUID-04990BCF-8228-459E-AFAA-9FAF1E2136E9

Selected Answer: D https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_isis/configuration/xe-3s/irs-xe-3s-book/ip6-route-isis-xe.html#GUID-04990BCF-8228-459E-AFAA-9FAF1E2136E9 single topology with no adjacency-check, so D is correct For single-topology IS-IS IPv6, routers must be set up to run the same set of address families. IS-IS checks consistency on hello packets and will reject hello packets that do not have the same set of configured address families. For example, a router running IS-IS for both IPv4 and IPv6 will not form an adjacency with a router running IS-IS for IPv4 or IPv6 only. To allow adjacency in a network with mismatched address families, the adjacency-check command in IPv6 address family configuration mode must be disabled. Enter the no adjacency-check command only when you are running IPv4 IS-IS on all your routers and you want to add IPv6 IS-IS to your network but need to keep all your adjacencies during the transition.

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_isis/configuration/15-mt/irs-15-mt-book/ipv__routing__is-is_multitopology_support_for_ipv_.pdf Transition from Single-Topology to Multitopology Support for IPv6 All routers in the area or domain must use the same type of IPv6 support, either single-topology or multitopology. A router operating in multitopology mode will not recognize the ability of the single-topology mode router to support IPv6 traffic, which will lead to holes in the IPv6 topology. To transition from single-topology support to the more flexible multitopology support, a multitopology transition mode is provided.

The multitopology transition mode lets a network operating in single-topology IS-IS IPv6 support mode keep working while routers are upgraded to include multitopology IS-IS IPv6 support. While in transition mode, both types of TLVs (single-topology and multitopology) are sent in LSPs for all configured IPv6 addresses, but the router still operates in single-topology mode (that is, the topological restrictions of the single-topology mode are still in effect). After all routers in the area or domain have been upgraded to support multitopology IPv6 and are operating in transition mode, transition mode can be removed from the configuration. Once all routersin the area or domain are operating in multitopology IPv6 mode, the topological restrictions of single-topology mode are no longer in effect.

Sorry folks, the answer is indeed C

Selected Answer: B https://rayka-co.com/lesson/isis-ipv6-multi-topology/

Selected Answer: B According to OCG, page 120: "IS-IS support IPv6 as a separate protocol(...)" and page 121 "IS-IS provides support for IPv4 and IPv6 as separate topologies" -> this means it needs two separate topologies for different address families = MULTITOPOLOGY.

Selected Answer: C https://datatracker.ietf.org/meeting/105/agenda/v6ops-drafts.pdf Single Topology: 4.1 Third Paragraph Transition: 4.2.1 First Paragraph

No, it is C. On the same page of OCG you mention, in the same paragraph, it says at the end : "It is important to know that if IPv4 and IPv6 are sharing the same topologies with the same router levels, there is no need for multi-topology or transition features."

Selected Answer: A In OCG on page 121 it says "IS-IS provides support for IPv4 and IPv6 as separate topologies" so the multi topology setting is required without transition

Further reading says that single topology with Dual Stack will also work, so it could still be either single or multi topology for this question