From: Brian McGahan (bmcgahan@internetworkexpert.com)
Date: Tue Aug 09 2005 - 12:44:28 GMT-3
George,
Typically the subnet mask of an IPv6 endpoint will be /64, but
you can configure it however necessary to meet your design requirements.
I would not bang your head against this one too much as site local
addresses are already deprecated:
http://www.internetworkexpert.com/rfc/index.php?rfc=3879
HTH,
Brian McGahan, CCIE #8593
bmcgahan@internetworkexpert.com
Internetwork Expert, Inc.
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> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> George Papadimitriou
> Sent: Tuesday, August 09, 2005 10:03 AM
> To: ccielab@groupstudy.com
> Cc: george_papadimitriou@yahoo.com
> Subject: ipv6 - subnet masks
>
> Hi group,
>
> A quick question, may seem obvious to many.
>
> I'm a bit confused with what we do when we're asked to configure site-
> local ipv6 addresses but the subnet mask is not specified. According
to:
>
http://www.cisco.com/univercd/cc/td/doc/product/software/ios123/123cgcr/
ip
> v6_c/sa_bconn.htm#wp1027186
>
> the 16-bit SLA field is the subnet field.
>
> Let's say a site-local address has to be configured on an interface
and
> the subnet field in the ipv6 address must be the same (hex equivalent)
as
> the subnet field of the interface's ipv4 address. In that case, on an
> interface with 172.16.15.1/24 do we have to configure
FEC0::F:0:0:0:1/64
> or are we free to configure a longer subnet mask, e.g. FEC0::F:1/125 ?
>
> In NMC scenario 1, the SLA and subnet fields are explicitly given and
> site-local ipv6 subnets are configured "within" SLAs, e.g.
> FEC0:0:0:A::7B:2/125, where A is the SLA and 7B is the ipv6 subnet ID.
>
> My understanding is:
> - If the SLA is explicitly given then it has to occupy the last
16-bits of
> the first half of the ipv6 address, but further subnetting is
possible
> with longes subnet masks and subnet IDs
>
> - If the SLA is not given and a site-local address is required with a
> particular subnet ID then that subnet ID will have to go into the SLA
> field.
>
> What are your views on this?
>
> Thanks,
> George
>
>
>
>
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