[bdNOG] Plain Simple v4 routing over v6

Manjan Ahmed Chowdhury manjan.ahmed.chowdhury at gmail.com
Sat Mar 7 07:58:41 BDT 2020

Hello Everyone,
This is my first interaction with bdNOG and looking forward to some
positive feedback. Unfortunately this is pretty simple question and
everyone might think of flame throwing but I would really appreciate a
positive feedback on the question. Recently I was asked the question in an
Interview that why cannot we simply route v4 in an v6 network without the
help of a Tunneling protocol or such.
My answer was something like following but it seemed that the Board was not
happy with the question and neither did they answer it:
1. TTL field vs Hop-Limit field due to which when a v4 route is received on
a v6 host the next-hop is changed from v4 to v6 so the TTL field is gone or
reset to 0.
2. v4 Routes are associated with an Interface and v4 address whereas in v6
a route is associated with a Link and uses Link Local address only.
3. In v4 reverse route lookups are done using ARP resolution to find the
next-hop interface whereas in v6 there is no concept of ARP as it is part
of stateless autoconfiguration with predefined algorithms.

Can anyone please let me know if I was wrong in any statement?

Best Regards,
Manjan Ahmed Chowdhury
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