[bdNOG] Plain Simple v4 routing over v6

Tue Mar 10 11:55:17 BDT 2020

Hi Manjan,

Firstly, thanks for sharing the idea with the community. As Scott said,
these NOGs are for knowledge and experience sharing ..... so nobody is
going to think anything else...

Secondly, to extend Scott's answer, we need to understand how these
protocols are different. Because they are designed in that way. If you see
the ipv4 & ipv6 packet header comparison, you will get the idea why one
protocol doesn't talk to another. Because their packets are formed in
different structure in header.

As you know that the packet will be considered as per its structure, ipv4
and ipv6 can't talk to each other because of their difference in packet
header. Below picture will give you the idea of difference between them.
The left one is for ipv4 and the right one is for ipv6. If you want to know
more details on ipv6 protocol, you can look into the below link as well.

http://wiki.bdnog.org/lib/exe/fetch.php/bdnog11/1.1.2-ipv6-protocol.pdf

[image: image.png]

BR
Zobair

On Tue, Mar 10, 2020 at 1:58 AM Scott Weeks <surfer at mauigateway.com> wrote:

>
>
> Hello,
>
> I didn't see an answer to your question, so I thought I'd try.
>
> First: "everyone might think of flame throwing but I would really
> appreciate a positive feedback on the question"
>
> I would hope no one throws flame over something like this.  I
> believe this is one thing a NOG is for and hope anyone would feel
> comfortable asking these questions here.  We all learn better in
> a collaborative environment.
>
> ::  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.
>
> Your question is not answered by this part of my response, but
> for others the tunneling protocols are a transition mechanism,
> which should be avoided at this point for many networks.  Opt
> for dual stack when designing an IPv6/IPv4 network.  The two
> tunneling transition mechanisms are 4in6 and 6in4.
>
> https://en.wikipedia.org/wiki/6in4
>
> https://en.wikipedia.org/wiki/4in6
>
> The reason you can't do it without a tunnel is the protocols are
> not compatible with each other.  If an IPv4 address showed up on
> an IPv6 interface the receiving router would have no idea what
> to do with it.  Likewise, if an IPv6 addressed packet showed up
> on an IPv4 interface the router has no idea what to do with it.
> In both cases the packet would be dropped as it's not understood.
> Perhaps that'd show up in the interface errors as an "unknown
> protocol"?
>
> The tunnels are a way to 'hide' the underlying protocol from the
> transporting protocol until the underlying protocol's packet gets
> to a router that understands it.
>
> Hopefully, someone with more experience than me can speak up
> with better details that I used.
>
> scott
>
>
>
>
>
>
> --- manjan.ahmed.chowdhury at gmail.com wrote:
>
> From: Manjan Ahmed Chowdhury <manjan.ahmed.chowdhury at gmail.com>
> To: nog at bdnog.org
> Subject: [bdNOG] Plain Simple v4 routing over v6
> Date: Sat, 7 Mar 2020 07:58:41 +0600
>
> 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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>
>
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