ipv6 pings

just wondering if someone can clarify this to me? these are pings examples between 2 routers in the same network segment . why are pings successful in the first and not in the 2nd?

2001:aaaa:bbbb::1/48 pings 2001:aaaa:bbbb::2/54      = good >> why? because it shares major prefix length? arent these 2 different networks indicated by the / ?  
2001:aaaa:bbbb::1/48 pings 2001:aaaa:bbbb:400::3/54 = bad >> why? these are 2 different networks but why did the pings go through on the first?
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Rich WeisslerProfessional Troublemaker^h^h^h^h^hshooterCommented:
the /48 and /54 denote how much of the address is the link/subnet portion.  In the first case, they are on the same network because:
2001:aaaa:bbbb (which is the first 48 bits) = 2001:aaaa:bbbb:00 (which would be the first 56 bits)  (The second host would assume the first is on it's same link, so would send the response back to it directly.)

In the second case:
2001:aaaa:bbbb != 2001:aaaa:bbbb:40  
So, in the second case, I believe the hose with the /54 would send the response to it's default gateway rather than back to the first host.

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