My initial sense... for SPF-based protocols (OSPF/IS-IS) it actually
makes little difference whether they do or don't. If they are
forwarding directly to host in their subnet (my preferred term for
what Ole calls a LAN), and only the router beyond them is advertising
the prefix, they will in the normal case be the router en route to the
advertising router. As such, while it is possible to construct
exception cases, For SPF-based protocols it is sufficient of only the
router they learned it from advertises the prefix.
Distance vector protocols like RIP are a different case because we now
have to put a funny case in them - "if I learned it from another
router in the subnet but I am in the same subnet, ..." In distance
vector protocols, yes, they should advertise it away from the subnet.
On Jan 12, 2010, at 11:16 PM, Mark Smith wrote:
On Tue, 12 Jan 2010 21:07:53 -1000
Ralph Droms <[email protected]> wrote:
Ole - I have a problem with some of the terminology in the
requirements: specifically, the use of "LAN" is ambiguous and should,
I think, be replaced with some more specific like "to all links on
which the device has an active interface".
One issue with this mechanism is what to do if the "ULA-router"
flaps? Will another router begin to advertise a new ULA? Will the
original router honor the new ULA and refrain from advertising its
own
ULA when it comes back up? All of which leads to a "ULA-flap" in the
subscriber network, which seems like a bad event.
IIRC, Appletalk did this sort of thing, with "seed" routers etc. It
might be worth seeing if it dealt with these sorts of situations, and
how.
Another related issue, although not so much of one with small
residential/SOHO offices, is if a router configures it's local
interface with prefixes in other routers' RAs, should the learning
router then automatically announce those prefixes into any IGPs or
EGPs
its operating? I think Appletalk did, however these days I'd think
it'd
be better not to.
Regards,
Mark.
- Ralph
On Jan 12, 2010, at 7:50 AM 1/12/10, 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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