[EMAIL PROTECTED] wrote:
Hi all, as we all know Link Local addresses and communicating through them are
a must in an IPv6 environment. Without it Neighbor Discovery will not work and
so address resolution.
Our system enables one to set an MTU for and IPv6 address. So it is very much
possible to set the MTU also for the Link Local IPv6 address.
The question I have for this forum is what is the MTU value that should be set
for this Link Local address?
Possibilities:
1. 1280 --- the reason is that this value would guarantee a Neighbor
Discovery operation since all devices must support at least this MTU.
2. The MTU of NIC device associated with this Link Local --- All of the
Neighbor Discovery messages (even the future ones) are guaranteed to be less
than 1280 so I shouldn't worry about it.
3. ???
Thanks for your answers!
Shuki
Until it has heard from a router connected to a link a host should
assume the MTU is either
1. The fixed well-known MTU associated with the type of link with which
the link local address is associated, if it has one (e.g., Ethernet), or
2. The guaranteed minimum MTU (1280 bytes) otherwise, where the link
type doesn't have a fixed MTU or if it is easier to decide later
The node cannot go wrong by initially assuming an MTU of 1280 bytes if
it prefers since the first few neighbor discovery etc packets are
generally quite small.
Assuming there is a router connected to the link and the link is of a
type that doesn't have a predetermined MTU (like token ring) or there
are bridged heterogeneous link layers (or just 'cos the administrator
thinks it is a good idea), the Router Advertisement should contain an
MTU option. Once this has been received, the host knows what MTU to use
on that link.
If it turns out that this is an isolated link with no routers or the
router doesn't provide an MTU option, the host can carry on with its
original choice, or if it started with 1280 bytes and knows the fixed
link type MTU it can use that value in future.
See RFC2461 (soon to be superseded by draft-ietf-ipv6-rfc2461bis-08 -
but that doens't alter any of this).
Regards,
Elwyn
Shuki Sasson
Principal Engineer, Network Storage Group
EMC²
where information lives
Fax: 508 305 9026
Phone: 508 305 8515
Cell: 617 834 4258
Pager: 877 919 0794
Email: [EMAIL PROTECTED]
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