Re: Abnormal behaviour of ping6

[Marc Blanchet <Marc.Blanchet@viagenie.qc.ca>]

--On Mercredi 20 octobre 2004 17:33 +0530 Sharmila <shard@intoto.com> wrote:

> Hi Marc,
>         Thanks a lot for ur reply.With the ipaddresses and mask suggested
> by you,everything is working fine.I am able to ping from Host1 to Host2
> successfully all the times.traceroute6 and tracepath6 also worked fine.
>         But,I have two questions to ask you and everybody:
>         1)According to my understanding site-local addresses in ipv6 are
> same as private ipaddresses in ipv4.If site-local addresses are being
> deprecated,which addresses should we use on private LANs??
- site-local were similar to IPv4 private address space, and had the 
potential to bring the same issues, which led to NATs.
- a (good) decision was made to deprecate and replace it by a better 
private address space, which is unique for any organisation that uses it. 
See: 
<http://www.ietf.org/internet-drafts/draft-ietf-ipv6-unique-local-addr-06.txt>
- you should avoid private address space as much as possible. If you ever 
need it, then use the one describe in the previous draft.
- be aware that the draft contains possible IANA assignments not yet done.

>         2)I could not understand why netmask /80 is illegal in ipv6?

design choice:
- 48 bits are <current> mac address length. but ieee has designed 64 mac 
address.
- eui-64 is a mechanism to "convert" 48 bit mac address to 64 bit mac 
address.
- IPv6 interface id is 64 bits and contains the eui-64. See: 
<http://www.ietf.org/rfc/rfc3513.txt>

so in ipv6, address plans are easy. "subnet mask" is always /64. a /64 is 
large enough to hold any possible number of hosts on a link. a /48 is for a 
site. so you only have to worry to number the subnets...

Marc.

> I
> thought ,I would use 48 bits for interface-id and remaining 80 as
> prefix.Why am I wrong in thinking so? When I did ifconfig with /80 ,it
> accepted and even displayed the address with /80 prefix.then why does the
> kernel (probably) set it to 64.
>         It would be very kind of u all if you can clarify me in these
> things.
>
> Thanks again for previous mail.
>
> Expecting more help from u,
> Sharmila
>
> At 06:50 AM 10/20/2004, Marc Blanchet wrote:
>
> - your "netmask" is /80. illegal in ipv6. should be /64.
> - the kernel probably sets it to /64 anyway. if you then look at your
> config and substitute /80 by /64, then all your hosts appear to be on the
> same link, where they aren't.
>
> - use /64 and do addressing for the 2 links. example:
>
>
> host1 eth0  =   fec0::1:e2d2:50:fcb2:7251 / 64
> router eth0  =   fec0::1:e2d2:50:fcb1:de7b / 64
> router eth1  =   fec0::2:a4b4:11:111b:9dd3 / 64
> host2 eth0   =  fec0::2:a4b4:50:fcb2:4574 / 64
>
>
> - fec0, site-local, is currently being deprecated. You can still use it
> for testing purposes, but don't plan to do a whole ipv6 addressing plan
> with this.
>
> Marc.
>
> --On Mardi 19 octobre 2004 18:28 +0530 Sharmila <shard@intoto.com> wrote:
>
>
> Hi all,
>                 I am a new user of Ipv6 and I am using the following
> simple setup:
> Host1------Router--------Host2
> Host1,Host2 & router are linux(kernel version 2.4.18-4 ) pcs with ipv6
> insmoded .(Dual Stack is present  on all 3 m/cs).On router,I have enabled
> forwarding.
>
> The ipv6 addresses are as follows:
>
> host1 eth0  =   fec0::e2d2:50:fcb2:7251 / 80
> router eth0  =   fec0::e2d2:50:fcb1:de7b / 80
> router eth1  =   fec0::a4b4:11:111b:9dd3 / 80
> host2 eth0   =  fec0::a4b4:50:fcb2:4574 / 80
>
> Added corresponding routes on host1 and host2
>
> Now the problem is , ping6 from host1 to host2 is successful sometimes
> and failure sometimes.In case of failure,it gives "Destination not
> reachable:Address unreachable" message.
>
> Why is it behaving abnormally?? Am I missing some configuration ? Or is
> the problem with my m/cs?
> Also, are there are any better test tools?? Please help me in this regard.
>
> Thanks in advance,
> Sharmila
>
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>
>
> D.Sharmila
> Intoto Software (India) Pvt. Ltd.,
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