Subject: [lisp] #92: Restriction on number of encapsulations (comment 13 reported by Y. Rekhter)

From: "lisp issue tracker" <[email-masked]>
Date: Wed, 28 Apr 2010 05:12:52 -0000

#92: Restriction on number of encapsulations (comment 13 reported by Y. Rekhter)
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Reporter:  wmhaddad@…          |       Owner:                 
    Type:  technical           |      Status:  new            
Priority:  major               |   Component:  draft-ietf-lisp
Severity:  -                   |    Keywords:                 
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 Section 4:

    An additional LISP header may be prepended to packets by a transit
    router (i.e.  TE-ITR) when re-routing of the path for a packet is
    desired.  An obvious instance of this would be an ISP router that
    needs to perform traffic engineering for packets in flow through its
    network.  In such a situation, termed Recursive Tunneling, an ISP
    transit acts as an additional ingress tunnel router and the RLOC it
    uses for the new prepended header would be either a TE-ETR within the
    ISP (along intra-ISP traffic engineered path) or a TE-ETR within
    another ISP (an inter-ISP traffic engineered path, where an agreement
    to build such a path exists).

    This specification mandates that no more than two LISP headers get
    prepended to a packet.  This avoids excessive packet overhead as well
    as possible encapsulation loops.  It is believed two headers is
    sufficient, where the first prepended header is used at a site for
    Location/Identity separation and second prepended header is used
    inside a service provider for Traffic Engineering purposes.

 The restriction on the number of encapsulations seems impossible to
 enforce, and therefore somewhat pointless.  Worse, it seems harmful; in
 order to foil ISP TE, all one needs to do is place an extra header in the
 LISP packets.  If the spec is obeyed,
 re-encapsulation will be prevented.

 The restriction on the number of headers would also seem to preclude host-
 based implementations of LISP being located behind site-based LISP
 routers.

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Ticket URL: <http://trac.tools.ietf.org/wg/lisp/trac/ticket/92>
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