Fred - I disagree with:
If I have more than one router on a LAN and one is responding to
RS's with RAs, the others should not do so on that interface, but
should inherit their prefix from the router that is responding.
If the subscriber network is multihomed, with different prefixes from
different SPs, should each router advertise its own prefixes?
- Ralph
On Jan 12, 2010, at 4:09 PM 1/12/10, Fred Baker wrote:
I don't see anything in the RFC about the behavior of routers in
this context; in point of fact, I don't see anything about routers
coming up and finding each other. I would interpret that as "routers
are expected to be configured, manually or dynamically, as opposed
to determining prefixes and addresses dynamically".
It seems to me that it is very rational to consider a router as
getting an address on an interface in three possible ways:
- manual configuration
- DHCP [RFC 3315]
- via a Router Advertisement from another router
manual configuration takes precedence over dynamic configuration,
and dynamic configuration over an RA. But if a router has neither of
the first two, then I would agree that on that interface it is
operating as a host until something changes that.
By that logic, it should send an RS, and with the resulting RA it
should configure itself with both a prefix for the interface and an
address within the LAN. Absent the prefix for the interface, it
would have to forward datagrams to the other router in order to know
they belonged on the local LAN. Having "inherited" that
configuration, if you will, there is something it should *not* do:
it should not issue an RA with that prefix while it is in contact
with said other router, as doing so is redundant. It should only
send RAs if it loses contact with the original router advertising
the prefix.
Note that this is suddenly not specific to ULAs; it is also true of
global addresses. If I have more than one router on a LAN and one is
responding to RS's with RAs, the others should not do so on that
interface, but should inherit their prefix from the router that is
responding.
On Jan 12, 2010, at 9:50 AM, Ole Troan wrote:
hi,
a question arose from work I'm doing with the BBF and their CPE
requirements document (TR-124/WT-192). an issue has been raised
with regards to a requirement about CPE routers automatically
offering ULA addresses on the LAN. in the case of multiple CPE
routers on a link, the suggestion is the following two requirements:
LAN.ADDRESSv6. 3 The device MUST send a Router Solicitation to the
LAN, to determine if there
are other routers
present. MUST
LAN.ADDRESSv6. 4 If the device determines other routers are present
in the LAN, and that another
router is advertising
a ULA prefix, the device MUST be configurable to
automatically use
this information to decide not to advertise its own
ULA prefix. MUST
any opinion on these requirements and how they compare with
expected behavour as specified in RFC4861?
cheers,
Ole
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