Re: [CARD Technical Issue] U flag and Unsolicited CARD

> > The draft also contains no guidelines about unsolicited. What is the
> default
> > intermessage time on broadcast/multicast? What about the port number and
> > TTL?
> >
> [eunsoo] Since it is the AR that sends the unsolicited CARD replies, the
> transmission rate will depend on the configuration. We tried to avoid
> recommending an arbitrary number as default values without base.
>

A default rate must be specified. The IESG will insist on this. See RFC 2608
for an example.

> The same port number as the solicited CARD reply is used for the
unsolicted
> CARD reply.
>

OK.

> What do you think would be the proper TTL for the unsolicited CARD reply?
I
> thought TTL 1 should be fine between MN-AR.
>

If you make it 255, then the reply must have come from a node on the same
link. This is a cheap way to prevent an offlink attacker from sending bogus
CARD replies. RFC 2461 uses this technique. The node should reject the
message if the TTL is not 255.

> > Also, I'm not clear about why an unsolicited message needs to be marked.
> How
> > would a MN utilize the U flag? How would processing of a solicited v.s.
> > unsolicited message differ?
> >
> >
>
> For solicited CARD replies, the receiver needs to match the reply to the
> request by the sequence number. For unsolicited replies, there is no
> matching request and thus the receiver should be able to distinguish the
> unsolicted replies from the solicited ones.
>

How are replay attacks prevented in the multicast case?

            jak