[RRG] Re: LISP gleaning looks insecure and therefore unusable

[Dino Farinacci <dino@cisco.com>]

> Short version:    Gleaning seems to be completely insecure,
>                  so I can't imagine how it could be useful.

You just don't use a glean until you complete a Map-Request/Map-Reply  
exchange. That way you test the outer SA of the packet to echo a  
packet back to you with the nonce you provided.

Not only do you want to verify the locator, but you want to get the  
other locators associated with the EID-prefix.

> do not contain the word "glean".
>
> Here is my understanding of gleaning, by way of an example:
>
>   HostA-->--R1==>==R2==>==R3-->--HostB
>
> HostA sends a packet to HostB.  HostB's address is within a
> LISP-mapped EID prefix.  R1 functions as an ITR and (after gaining
> the mapping information for HostB's address) encapsulates the packet
> and tunnels it "==" to R3 which acts as an ETR.  The decapsulated
> packet is sent to HostB.  (Also, perhaps R1 had no mapping, but the
> packet gets to R3 via the ALT network.)
>
> As I understand it, "gleaning" involves R3, as an ETR, taking the
> outer source address of the packet it received (R1's address) as an
> RLOC location, presuming it to be the address of an ETR, and the
> inner packet's source address (HostA's address) and presuming this
> to be an EID.

Yes, so the Map-Reply that responds to the Map-Request also provides  
the EID-prefix associated with the inner SA (the source EID) from the  
invoking packet.

> The purpose is to have at least this gleaned mapping information:
>
>  EID (HostA's address) mapped to RLOC (R1's address)
>
> ready, without any delay due to mapping lookups, for the likely
> event that HostB will soon send a packet right to left to HostA.

Right, but you get an unvalidated partial mapping that one has to  
decide if it wants to use. In our prototype, we have gleaning turned  
off by default, but when enabled, we also allow you to verify the  
glean. So if you turn that off, you use the glean information right  
away, otherwise you drop packets until the Map-Reply comes back.

> The basic draft-farinacci-lisp-06 document can be hard to
> understand, because it primarily (or solely?) applies to LISP
> variants 1.0 and 1.5.  Where do LISP-NERD and LISP-ALT fit into
> this?  The reader is trying to construct a concrete understanding of
> how NERD and ALT would work while reading multiple documents which
> reference each other in general, but perhaps not in sufficient detail.

There is a datagram based mechanism to send and receive Map-Replies  
from the main spec. But how and where Map-Requests or Data Probes are  
sent, depends on the mapping database.

So Data Probes are used in:

1) LISP 1.0.
2) LISP-ALT

And Map-Requests only are used in:

1) LISP-CONS
2) Gleaning

And both Data Probes and Map-Requests are used in:

1) LISP-ALT

And Nerd doesn't use any Data Probe or Map-Request because the mapping  
data comes to you via the push mechanism.

Dino



--
to unsubscribe send a message to rrg-request@psg.com with the
word 'unsubscribe' in a single line as the message text body.
archive: <http://psg.com/lists/rrg/> & ftp://psg.com/pub/lists/rrg