This topic is to discuss the following lesson:
I was wondering if you can clarify something for me. From me reading of this lesson, I understand that the solicited node multicast address is formed by joining the last 6 hex of the link local address to the FF02::1:ff address, correct ?
Now, the confusion comes in when we add a IPv6 unicast address, your example being:
How, is the solicited multicast address now:
Why did you take the last 6 hex from the Ipv6 unicast address and not the link local address ?
The solicited node multicast address is generated for each IPv6 address on the interface, there’s one for the link local address and for each global unicast address that you have configured.
If we are only taking last 6 hex then multiple hosts on the same LAN may join to the same multi-cast group. As many hosts may have the MAC addresses whose last 24 bits are same. Is generating unique “solicited multi-cast address” not our intention ?
6 hexadecimal characters are 24 bits. The last 24 bits of the MAC address is the “vendor assigned” part. If you have two network cards from the same vendor then the last 24 bits should be unique.
Theoretically, it could be possible that you have two network cards from different vendors that have the same 24 vendor assigned bits but the odds are extremely small
It is possible though to have two IPv6 addresses that use the same solicited node address. This is no problem though…both hosts will listen to the multicast group address and if needed, discard the packet that isn’t for them.