Last Updated on August 1, 2021 by Admin 1
Refer to the following exhibit, where three routers have EIGRP for IPv6 enabled on them:
What is the next-hop address when rtrB advertises the 2001:5050:D402:B333::/64 IPv6 subnet to rtrC?
The next-hop address when rtrB advertises the 2001:5050:D402:B333::/64 IPv6 subnet to rtrC is FE80::3230:30FF:FE30:3030/64. In routers with EIGRP for IPv6 enabled on them, the next-hop address is the IP address of the interface that advertises routes. The next-hop addresses should be link-local addresses. Link-local addresses are IPv6 unicast addresses that are automatically assigned to the router interfaces. These addresses have the FE80::/10 prefix and the EUI-64 standard interface address.
EUI-64 is an IEEE standard that allows the determination of an IPv6 address from the MAC address of an interface. The 64 most significant bits should be specified in the ipv6 address command. The 64 least significant bits are determined by using the EUI-64 standard. The steps to determine the 64 least significant bits are as follows:
Divide the 48-bit MAC address into two 24-bit parts.
Embed FFFE (16 bits) between the two parts resulting in a 64-bit address.
If required, toggle the seventh bit of the first octet in the address. In EUI-64 format, if the seventh bit is 0, then the address is local. If the seventh bit is 1, the address is global.In this case, when rtrB advertises any route to rtrC, it advertises the interface with the MAC address 3030.3030.3030 as the next-hop. When the given steps are performed on the MAC address, it result in the EUI-64 standard address 3230.30FF.FE30:3030. This address is then appended to the FE80::/10 prefix. The resultant IPv6 link-local address of the interface is FE80::3230.30FF.FE30:3030/10.
The remaining three options are incorrect as their interface address is not in the EUI-64 standard.
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Identify IPv6 addressing and subnetting