From: George Papadimitriou (george_papadimitriou@yahoo.com)
Date: Tue Aug 09 2005 - 12:03:26 GMT-3
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/ipv6_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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