Subject: Re: [nemo] Jim's comments on Basic Support

From: Alexandru Petrescu <[email-masked]>
Date: Wed, 19 Nov 2003 21:32:32 +0100

Vijay Devarapalli wrote:
> hi Jim,
> 
> I have filed your comments as Issues 20 and 21 at 
> http://people.nokia.net/vijayd/nemo/issues.html.
> 
>> When the Mobile Router is at home, it MAY be configured to send 
>> Router Advertisements and reply to Router Solicitations on the 
>> interface attached to the home link.  The value of the Router 
>> Lifetime field MUST be set to zero to prevent other nodes from 
>> configuring the Mobile Router as the default router.
>> 
>> jak> What happens if the Mobile Router advertises prefix A on the 
>> home link, then moves and advertises prefix B? This could happen if
>>  the Mobile Router was configured for a particular prefix on the 
>> home link, then received a separate prefix when it moved away.

I agree there might be a problem if MR is allowed to advertise _any_
prefix (send RA's) on the visited link (be it prefix A, or a dynamically
acquired prefix B from HA).  I think that's why spec says MR SHOULD NOT
send RA's on the visited link.  What could be discussed is whether this
should be a "SHOULD NOT" or a "MUST NOT".

I suggest to keep it "SHOULD NOT".

>> A Mobile Router SHOULD NOT send unsolicited Router Advertisements 
>> and SHOULD NOT reply to Router Solicitations on any egress 
>> interface when that interface is attached to a visited link. 
>> However, the Mobile Router SHOULD reply with Neighbor 
>> Advertisements to Neighbor Solicitations received on the egress 
>> interface, for topologically correct addresses.
>> 
>> jak> What happens to hosts that are utilizing the router due to it
>>  having sent unsolicted RAs on the egress interface on the home
>> link when the router moves away?

So are you suggesting making it "MUST NOT"?

>> Wouldn't it be better just to prohibit the Mobile Router from 
>> responding to RSs and sending unsolicited RAs on its egress 
>> interface?

Prohibit that, maybe yes, but only when MR is away from home.

I suggest to keep it as SHOULD NOT, in order to allow for an extreme
case that is this:

MR attaches to AR.  A new MH attaches to same AR.  Fade AR disappear
away.  At this point, if MR does not send RA's on the visited link it
has no way of talking to MH.  This would be a limited case, and if MR
could send RA's in the ether (when AR is dead) then MH autoconfigures an
address and can talk directly to MR (of course, not using their home
addresses, and MH can not talk to LFN's inside the moving network).

I think this is the only reason that could be a "SHOULD NOT" instead of
a "MUST NOT".

>> A Mobile Router MUST NOT ignore Router Advertisements received on 
>> the egress interface.  The received Router Advertisements MAY be 
>> used for address configuration, default router selection or 
>> movement detection.
>> 
>> jak> In fact, it MUST utilize these as described in the base MIP6 
>> protocol for movement detection.

What the MIPv6 spec does not observe (even if the MN terminology
suggests so) is that that MN could be an MR and send RA's natively.
Thinking in a MIPv6 for hosts context exclusively does not make it
obvious that that MH might be able to talk to another MH, when they're
both under the same AR and when that AR disappears.

Alex