full pass

draft-ietf-lsvr-l3dl.xml

@@ -11,14 +11,14 @@
 <?rfc tocindent="yes"?>
 <?rfc tocompact="yes"?>
 
-<rfc category="std" docName="draft-ietf-lsvr-l3dl-01" ipr="trust200902">
+<rfc category="std" docName="draft-ietf-lsvr-l3dl-02" ipr="trust200902">
 
 <front>
 
   <title>Layer 3 Discovery and Liveness</title>
 
     <author fullname="Randy Bush" initials="R." surname="Bush">
-      <organization>Arrcus &amp; IIJ</organization>
+      <organization>Arrcus &amp; Internet Initiative Japan</organization>
       <address>
         <postal>
           <street>5147 Crystal Springs</street>
@@ -60,9 +60,9 @@
     protocols are used to build topology and reachability databases.
     These protocols need to discover IP Layer 3 attributes of links,
     such as logical link IP encapsulation abilities, IP neighbor address
-    discovery, and link liveness.  The Layer 3 Discovery and Liveness
+    discovery, and link liveness.  This Layer 3 Discovery and Liveness
-    protocol specified in this document collects these data, which are
+    protocol collects these data, which may then be disseminated using
-    then disseminated using BGP-SPF and similar protocols.</t>
+    BGP-SPF and similar protocols.</t>
 
   </abstract>
 
@@ -83,10 +83,10 @@
   <section anchor="intro" title="Introduction">
 
     <t>The Massive Data Center (MDC) environment presents unusual
-    problems of scale, e.g. O(10,000) devices, while its homogeneity
+    problems of scale, e.g. O(10,000) forwarding devices, while its
-    presents opportunities for simple approaches.  Approaches such as
+    homogeneity presents opportunities for simple approaches.
-    Jupiter Rising <xref target="JUPITER"/> use a central controller to
+    Approaches such as Jupiter Rising <xref target="JUPITER"/> use a
-    deal with scaling, while BGP-SPF <xref
+    central controller to deal with scaling, while BGP-SPF <xref
     target="I-D.ietf-lsvr-bgp-spf"/> provides massive scale-out without
     centralization using a tried and tested scalable distributed control
     plane, offering a scalable routing solution in Clos <xref
@@ -99,17 +99,16 @@
 
     <t>Layer 3 Discovery and Liveness (L3DL) provides brutally simple
     mechanisms for devices to <list style="symbols">
-      <t>Discover unique identities of devices/ports/... on a logical
-      link,</t> 
-      <t>Run Layer 2 keep-alive messages for session continuity,</t>
       <t>Discover each other's unique endpoint identification,</t>
-      <t>Discover mutually supported encapsulations, e.g. IP/MPLS,</t>
+      <t>Discover mutually supported layer 3 encapsulations,
+      e.g. IP/MPLS,</t>
       <t>Discover Layer 3 IP and/or MPLS addressing of interfaces of the
       encapsulations,</t>
-      <t>Enable layer 3 link liveness such as BFD, and finally</t>
       <t>Present these data, using a very restricted profile of a BGP-LS
       <xref target="RFC7752"/> API, to BGP-SPF which computes the
-      topology and builds routing and forwarding tables.</t>
+      topology and builds routing and forwarding tables,</t>
+      <t>Enable layer 3 link liveness such as BFD, and finally</t>
+      <t>Provide Layer 2 keep-alive messages for session continuity.</t>
     </list></t>
 
     <t>This protocol may be more widely applicable to a range of routing
@@ -133,7 +132,7 @@
       external components using the BGP routing protocol.  See <xref
       target="RFC7752"/>.</t>
       <t hangText="BGP-SPF">A hybrid protocol using BGP transport but
-      a Dijkstra SPF decision process.  See <xref
+      a Dijkstra Shortest Path First decision process.  See <xref
       target="I-D.ietf-lsvr-bgp-spf"/>.</t>
       <t hangText="Clos:">A hierarchic subset of a crossbar switch
       topology commonly used in data centers.</t>
@@ -141,7 +140,7 @@
       frame.  A full L3DL PDU may be packaged in multiple Datagrams.</t>
       <t hangText="Encapsulation:">Address Family Indicator and
       Subsequent Address Family Indicator (AFI/SAFI).  I.e. classes of
-      layer 2.5 and 3 addresses such as IPv4, IPv6, MPLS, ...</t>
+      layer 2.5 and 3 addresses such as IPv4, IPv6, MPLS, etc.</t>
       <t hangText="Frame:">A Layer 2 packet.</t>
       <t hangText="Link or Logical Link:">A logical connection between
       two logical ports on two devices.  E.g. two VLANs between the same
@@ -153,8 +152,8 @@
       since they are used by all widely deployed Layer 2 network
       technologies of interest, especially Ethernet.  See <xref
       target="IEEE.802_2001"/>.</t>
-      <t hangText="MDC:">Massive Data Center, commonly thousands of
+      <t hangText="MDC:">Massive Data Center, commonly composed of
-      TORs.</t>
+      thousands of Top of Rack Switches (TORs).</t>
       <t hangText="MTU:">Maximum Transmission Unit, the size in octets
       of the largest packet that can be sent on a medium, see <xref
       target="RFC1122"/> 1.3.3.</t>
@@ -201,7 +200,7 @@
     in interfaces with thousands of disaggregated prefixes.</t>
 
     <t>Therefore the L3DL protocol is session oriented and uses
-    incremental announcement and widrawal with hot restart, a la BGP
+    incremental announcement and widrawal with session restart, a la BGP
     (<xref target="RFC4271"/>).</t>
 
     </section>
@@ -247,7 +246,7 @@
     </figure>
 
     <t>There are two protocols, the inter-device per-link layer 3
-    discovery and the interface to the upper level BGP-like API:
+    discovery and the API to the upper level BGP-like routing prototol:
       <list style="symbols">
 
       <t>Inter-device PDUs are used to exchange device and logical link
@@ -272,21 +271,21 @@
   <section anchor="ilpo" title="Inter-Link Protocol Overview">
 
     <t>Two devices discover each other and their respective identities
-    by sending multicast HELLO PDUs (<xref target="hello"/>).  To allow
+    by sending multicast HELLO PDUs (<xref target="hello"/>).  To assure
     discovery of new devices coming up on a multi-link topology, devices
     on such a topology send periodic HELLOs forever, see <xref
     target="dhello"/>.</t>
 
     <t>Once a new device is recognized, both devices attempt to
-    negotiate and establish peering by sending unicast OPEN PDUs (<xref
+    negotiate and establish a session by sending unicast OPEN PDUs
-    target="open"/>).  In an established peering, the Encapsulations
+    (<xref target="open"/>).  In an established session, the
-    (<xref target="afisafi"/>) configured on an end point may be
+    Encapsulations (<xref target="afisafi"/>) configured on an end point
-    announced and modified.  Note that these are only the encapsuation
+    may be announced and modified.  Note that these are only the
-    and addresses on the announcing interface; though a device's
+    encapsuation and addresses configured on the announcing interface;
-    loopback interface(s) may also be announced.  When two devices on a
+    though a device's loopback and overlay interface(s) may also be
-    link have compatible Encapsulations and addresses, i.e. the same
+    announced.  When two devices on a link have compatible
-    AFI/SAFI and the same subnet, the link is announced via the BGP-LS
+    Encapsulations and addresses, i.e. the same AFI/SAFI and the same
-    API.</t>
+    subnet, the link is announced via the BGP-LS API.</t>
  
     <section anchor="ladder" title="L3DL Ladder Diagram">
 
@@ -302,7 +301,7 @@
       PDUs are optional; though at least one encapsulation SHOULD be
       agreed at some point.</t>
       
-      <t>The following is a ladder-style sketch of the L3DL protocol
+      <t>The following is a ladder-style diagram of the L3DL protocol
       exchanges:</t>
 
     <figure>
@@ -380,8 +379,8 @@
   <section anchor="transport" title="Transport Layer">
 
     <t>L3DL PDUs are carried by a simple transport layer which allows
-    long PDUs to occupy many Ethernet frames.  An L3DL frame is referred
+    PDUs to occupy many Ethernet frames.  An L3DL Ethernet frame is
-    to as a Datagram.</t>
+    referred to as a Datagram.</t>
 
     <t>The L3DL Transport Layer encapsulates each Datagram using a
     common transport header.</t>
@@ -402,7 +401,7 @@
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |        Datagram Length        |            Checksum           ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-~                               |           Payload...          |
+~                               |           Payload...          ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         </artwork>
       </figure>
@@ -411,9 +410,9 @@
     <list style="hanging">
 
       <t hangText="Version:">Seven-bit Version number of the protocol,
-      currently 0.  Values other than 0 are treated as errors.  The
+      currently 0.  Values other than 0 MUST BE treated as an error.
-      protocol version nees to be in one and only one place, so it is in
+      The protocol version nees to be in one and only one place, so it
-      the datagram as opposed to, for example, the PDU header.</t>
+      is in the datagram as opposed to, for example, the PDU header.</t>
 
       <t hangText="L:">A bit that set to one if this Datagram is the
       last Datagram of the PDU.  For a PDU which fits in only one
@@ -436,6 +435,12 @@
       thereof.</t>
 
       </list></t>
+
+    <t>To avoid the need for a receiver to reassemble two PDUs at the
+    same time, a sender MUST NOT send a subsequent PDU when a PDU is
+    already in flight and not yet acknowledged if it is an ACKed PDU
+    Type.</t>
+    
     </section>
 
   <section anchor="checksum" title="The Checksum">
@@ -528,7 +533,7 @@ uint32_t sbox_checksum_32(const uint8_t *b, const size_t n)
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    Sig Type   |        Signature Length       |               ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               +
-~                           Signature                           |
+~                           Signature                           ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         </artwork>
       </figure>
@@ -557,7 +562,7 @@ uint32_t sbox_checksum_32(const uint8_t *b, const size_t n)
 
       <t hangText="Signature Length:">The length of the Signature,
       possibly including padding, in octets.  If Sig Type is 0,
-      Signature Length must be 0.</t>
+      Signature Length MUST BE 0.</t>
 
       <t hangText="Signature:">The result of running the signature
       algorithm specified in Sig Type over all octets of the PDU except
@@ -636,10 +641,6 @@ uint32_t sbox_checksum_32(const uint8_t *b, const size_t n)
 
   <section anchor="hello" title="HELLO">
 
-    <t>WARNING: The second multicast address below is incorrect.  We
-    need to get a new assignment.  , which is what we really wanted with the second address
-    below.</t>
-
     <t>The HELLO PDU is unique in that it is encapsulated in a multicast
     Ethernet frame.  It solicits response(s) from other LLEI(s) on the
     link.  See <xref target="dhello"/> for why multicast is used.  The
@@ -649,13 +650,15 @@ uint32_t sbox_checksum_32(const uint8_t *b, const size_t n)
 
       <t hangText="01-80-C2-00-00-0E:">Nearest Bridge = Propagation
       constrained to a single physical link; stopped by all types of
-      bridges (including MPRs (media converters)).</t>
+      bridges (including MPRs (media converters)).  This SHOULD BE used
+      when the link is known to be a simple point to point link.</t>
 
       <t hangText="To Be Assigned:"> When a switch receives a frame with
       a multicast destination MAC it does not recognize, it forwards to
       all ports.  This destination MAC is to be sent when the interface
       is known to be connected to a switch.  See <xref
-      target="ieee"/>.</t>
+      target="ieee"/>.  This SHOULD BE used when the link may be a
+      multi-point link.</t>
 
       <?rfc subcompact="no"?></list></t>
 
@@ -664,11 +667,12 @@ uint32_t sbox_checksum_32(const uint8_t *b, const size_t n)
     exchange.</t>
 
     <t>When an interface is turned up on a device, it SHOULD issue a
-    HELLO.</t>
+    HELLO if it is to participate in L3DL sessions.</t>
 
-    <t>If a constrained destination address configured, see above, then
+    <t>If a constrained Nearest Bridge destination address is configured
-    the HELLO need not be repeated once a session has been created by an
+    for a point-to-point interface, see above, then the HELLO SHOULD NOT
-    exchange of OPENs.</t>
+    be repeated once a session has been created by an exchange of
+    OPENs.</t>
 
     <t>If the configured destination address is one that is propagated
     by switches, the HELLO SHOULD be repeated at a configured interval,
@@ -696,8 +700,8 @@ uint32_t sbox_checksum_32(const uint8_t *b, const size_t n)
     separate logical link.</t>
 
     <t>When a HELLO is received from a source MAC address with which
-    there is no established L3DL adjacency, the receiver SHOULD respond
+    there is no established L3DL session, the receiver SHOULD respond
-    with an OPEN PDU.  The two devices establish an L3DL adjacency by
+    with an OPEN PDU.  The two devices establish an L3DL session by
     exchanging OPEN PDUs.</t>
 
     <t>The Payload Length is zero as there is no payload.</t>
@@ -711,7 +715,7 @@ uint32_t sbox_checksum_32(const uint8_t *b, const size_t n)
 
     <t>Each device has learned the other's MAC Address from the HELLO
     exchange, see <xref target="hello"/>.  Therefore the OPEN and
-    subsequent PDUs are unicast, as opposed to the HELLO's multicast
+    subsequent PDUs MUST BE unicast, as opposed to the HELLO's multicast
     frame.</t>
 
 <!--
@@ -754,9 +758,10 @@ q-->
     <t>My LLEI is the sender's LLEI, see <xref target="llei"/>.</t>
 
     <t>AttrCount is the number of attributes in the Attribute List.
-    Attributes are single octets whose semantics are user-defined.</t>
+    Attributes are single octets the semantics of which are
+    operator-defined.</t>
 
-    <t>A node may have zero or more user-defined attributes, e.g.
+    <t>A node may have zero or more operator-defined attributes, e.g.:
     spine, leaf, backbone, route reflector, arabica, ...</t>
 
     <t>Attribute syntax and semantics are local to an operator or
@@ -767,19 +772,19 @@ q-->
     target="tlv"/>.</t>
 
     <t>Key Length is a 16-bit field denoting the length in octets of the
-    Key itself, not including the Auth Type or the Key Lengths.  If
+    Key itself, not including the Auth Type or the Key Length.  If there
-    there is no Key, the Auth Type and key Length MUST both be zero.</t>
+    is no Key, the Auth Type and key Length MUST both be zero.</t>
 
     <t>The Key is specific to the operational environment.  A failure to
-    authenticate is a failure to start the L3DL session, an ERROR PDU is
+    authenticate is a failure to start the L3DL session, an ERROR PDU
-    sent (Error Code 2), and HELLOs MUST be restarted.</t>
+    MUST BE sent (Error Code 2), and HELLOs MUST be restarted.</t>
 
-    <t>The Serial Number is that of the last received and processed
+    <t>The Serial Number is that of the last received and processed PDU.
-    Encapsulation PDU.  This allows a receiver sending an OPEN to tell
+    This allows a receiver sending an OPEN to tell the sender that the
-    the sender that the receiver wants to resume a session and the
+    receiver wants to resume a session and the sender only needs to send
-    sender only needs to send data more recent than the Serial Number.
+    data more recent than the Serial Number.  If this OPEN is not trying
-    If this OPEN is not trying to restart a lost session, the Serial
+    to restart a lost session, the Serial Number MUST BE set to
-    Number MUST be set to zero.</t>
+    zero.</t>
 
     <t>The Signature fields are described in <xref target="tlv"/> and in
     an asymmetric key environment serve as a proof of possession of the
@@ -791,19 +796,29 @@ q-->
     keep the session semantics alive.  The timing and acceptable drop of
     KEEPALIVE PDUs are discussed in <xref target="keepalive"/>.</t>
 
-    <t>If a sender of OPEN does not receive an ACK of the OPEN PDU Type,
+    <t>If a sender of OPEN does not receive an ACK of the OPEN PDU, then
-    then they MUST resend the same OPEN PDU, with the same Nonce.
+    they MUST resend the same OPEN PDU, with the same Nonce.  Resending
-    Resending an unacknowledged OPEN PDU, like other ACKed PDUs, SHOULD
+    an unacknowledged OPEN PDU, like other ACKed PDUs, SHOULD use
-    use exponential back-off, see <xref target="RFC1122"/>.</t>
+    exponential back-off, see <xref target="RFC1122"/>.</t>
 
     <t>If a properly authenticated OPEN arrives with a new Nonce from an
     LLEI with which the receiving logical link endpoint believes it
-    already has an L3DL session (OPENs have already been exchanged), the
+    already has an L3DL session (OPENs have already been exchanged), and
-    receiver MAY assume that the sending LLEI or entire device has been
+    the Serial Number in the OPEN is non-zero, the receiver SHOULD
-    reset.  If the Serial Number in the OPEN is zero, then all
+    establish a new session by sending an OPEN with the Serial Number of
-    discovered encapsulation data SHOULD be withdrawn via the BGP-LS API
+    the last data it received.  Each party MUST resume sending
-    and the recipient MUST respond with a new OPEN.  In this
+    encapsulations etc. subsequent to the other party's Sequence Number.
-    circumstance encapsulations SHOULD NOT be kept.</t>
+    And each MUST retain all previously discovered encapsulation and
+    other data.</t>
+
+    <t>If a properly authenticated OPEN arrives with a new Nonce from an
+    LLEI with which the receiving logical link endpoint believes it
+    already has an L3DL session (OPENs have already been exchanged), and
+    the Serial Number in the OPEN is zero, then the receiver MUST assume
+    that the sending LLEI or entire device has been reset.  All
+    previously discovered encapsulation data MUST NOT be kept and MUST
+    be withdrawn via the BGP-LS API and the recipient MUST respond with
+    a new OPEN.</t>
 
     </section>
 
@@ -836,7 +851,7 @@ q-->
     PDU, etc.</t>
 
     <t>The ACKed PDU is the PDU Type of the PDU being acknowledged,
-    e.g., OPEN or one of the Encapsulations.</t>
+    e.g., OPEN, one of the Encapsulations, etc.</t>
 
     <t>If there was an error processing the received PDU, then the EType
     is non-zero.  If the EType is zero, Error Code and Error Hint MUST
@@ -848,12 +863,21 @@ q-->
     error.</t>
 
     <t>The decimal value of EType gives a strong hint how the receiver
-    sending the ACK believes things should proceed.  The ETypes are
+    sending the ACK believes things should proceed:
-    listed in <xref target="iana-error"/>.  Someone stuck in the 1990s
+    <list style="empty">
-    might think of the error codes as 0x1zzz, 0x2zzz, etc.  They might
+<?rfc subcompact="yes"?>
-    be right.  Or not.</t>
+        <t>0 - No Error, Error Code and Error Hint MUST be zero</t>
+        <t>1 - Warning, something not too serious happened, continue</t>
+        <t>2 - Session should not be continued, try to restart</t>
+        <t>3 - Restart is hopeless, call the operator</t>
+        <t>4-15 - Reserved</t>
+<?rfc subcompact="no"?>
+        </list></t>
 
-    <t>The Error Code indicates the type of error.</t>
+    <t>The Error Codes, noting protocol failures listed in thi document,
+    are listed in <xref target="iana-error"/>.  Someone stuck in the
+    1990s might think the catenation of EType and Error Code as an echo
+    of 0x1zzz, 0x2zzz, etc.  They might be right; or not.</t>
 
     <t>The Error Hint is any additional data the sender of the error PDU
     thinks will help the recipient or the debugger with the particular
@@ -873,8 +897,7 @@ q-->
       case of this ACK failure.</t>
 
       <t>If the link is broken at layer 2, retransmission MAY BE retried
-      when the link comes back up if data have not changed in the
+      when the link is restored.</t>
-      interim.</t>
 
       </section>
       
@@ -887,11 +910,10 @@ q-->
     session is considered established, and the devices SHOULD exchange
     L3 interface encapsulations, L3 addresses, and L2.5 labels.</t>
 
-    <t>The Encapsulation types the peers exchange may be IPv4
+    <t>The Encapsulation types the peers exchange may be IPv4 (<xref
-    Announcement (<xref target="ipv4"/>), IPv6 Announcement (<xref
+    target="ipv4"/>), IPv6 (<xref target="ipv6"/>), MPLS IPv4 (<xref
-    target="ipv6"/>), MPLS IPv4 Announcement (<xref target="mpls4"/>),
+    target="mpls4"/>), MPLS IPv6 (<xref target="mpls6"/>), and/or
-    MPLS IPv6 Announcement (<xref target="mpls6"/>), and/or possibly
+    possibly others not defined here.</t>
-    others not defined here.</t>
 
     <t>The sender of an Encapsulation PDU MUST NOT assume that the peer
     is capable of the same Encapsulation Type.  An ACK (<xref
@@ -937,12 +959,12 @@ q-->
         </artwork>
       </figure>
 
-      <t>The 24-bit Count is the number of Encapsulations in the
-      Encapsulation list.</t>
-
       <t>An Encapsulation PDU describes zero or more addresses of the
       encapsulation type.</t>
 
+      <t>The 24-bit Count is the number of Encapsulations in the
+      Encapsulation list.</t>
+
       <t>The Serial Number is a monotonically increasing 32-bit value
       representing the sender's state in time.  It may be an integer, a
       timestamp, etc.  On session restart (new OPEN), a receiver MAY
@@ -950,7 +972,7 @@ q-->
       send newer data.</t>
 
       <t>If a sender has multiple links on the same interface, separate
-      state: data, ACKs, etc. must be kept for each peer.</t>
+      state: data, ACKs, etc. must be kept for each peer session.</t>
 
       <t>Over time, multiple Encapsulation PDUs may be sent for an
       interface as configuration changes.</t>
@@ -988,9 +1010,10 @@ q-->
         </artwork>
       </figure>
 
-      <t>An Encapsulation PDU of Type T may announce new and/or withdraw
+      <t>Each encapsulation in an Encapsulation PDU of Type T may
-      old encapsulations of Type T.  It indicates this with the Ann/With
+      announce new and/or withdraw old encapsulations of Type T.  It
-      Encapsulation Flag, Announce == 1, Withdraw == 0.</t>
+      indicates this with the Ann/With Encapsulation Flag, Announce ==
+      1, Withdraw == 0.</t>
 
       <t>Each Encapsulation interface address in an Encapsulation PDU is
       either a new encapsulation be announced (Ann/With == 1) (yes, a la
@@ -1006,20 +1029,18 @@ q-->
       be marked as primary for a particular encapsulation type.</t>
 
       <t>An Encapsulation interface address in an Encapsulation PDU MAY
-      be marked as a loopback, in which case the Loopback bit is
+      be marked as a loopback, in which case the Loopback bit is set.
-      set.</t>
+      Loopback addresses are generally not seen directly on an external
-
+      interface.  One or more loopback addresses MAY be exposed by
-      <t>Loopback addresses are generally not seen directly on an
+      configuration on one or more L3DL speaking external interfaces,
-      external interface.  One or more loopback addresses MAY be exposed
-      by configuration on one or more L3DL speaking external interfaces,
       e.g. for iBGP peering.  They SHOULD be marked as such, Loopback
       Flag == 1.</t>
 
       <t>Each Encapsulation interface address in an Encapsulation PDU is
       that of the direct 'underlay interface (Under/Over == 1), or an
       'overlay' address (Under/Over == 0), likely that of a VM or
-      container guest bridged on to the interface with an underlay
+      container guest bridged or configured on to the interface already
-      address.</t>
+      having an underlay address.</t>
       
       </section>
 
@@ -1053,7 +1074,8 @@ q-->
         </artwork>
       </figure>
 
-      <t>The 24-bit Count is the number of IPv4 Encapsulations.</t>
+      <t>The 24-bit Count is the number of IPv4 Encapsulations being
+      announced and/or withdrawn.</t>
 
       </section>
 
@@ -1094,7 +1116,8 @@ q-->
           </artwork>
         </figure>
     
-      <t>The 24-bit Count is the number of IPv6 Encapsulations.</t>
+      <t>The 24-bit Count is the number of IPv6 Encapsulations being
+      announced and/or withdrawn.</t>
 
       </section>
 
@@ -1160,7 +1183,8 @@ q-->
         </artwork>
       </figure>
     
-      <t>The 24-bit Count is the number of MPLSv4 Encapsulations.</t>
+      <t>The 24-bit Count is the number of MPLSv4 Encapsulation being
+      announced and/or withdrawns.</t>
 
       </section>
 
@@ -1169,7 +1193,7 @@ q-->
       <t>The MPLS IPv4 Encapsulation describes a logical link's ability
       to exchange labeled IPv4 packets on one or more subnets.  It does
       so by stating the interface's addresses, the corresponding prefix
-      lengths, and the corresponding labels which will be accepted fpr
+      lengths, and the corresponding labels which will be accepted for
       each address.</t>
 <!--
     protocol "PDU Type = 7:8,Payload Length:32,Count:24,Serial Number:32,Encaps Flags:8,MPLS Label List ...:16,IPv6 Address:128,Prefix Len:8,more ...:8,Sig Type:8,Signature Length:16,Signature ...:32"
@@ -1203,14 +1227,9 @@ q-->
         </artwork>
       </figure>
 
-      <t>The 24-bit Count is the number of MPLSv6 Encapsulations.</t>
+      <t>The 24-bit Count is the number of MPLSv6 Encapsulations being
+      announced and/or withdrawn.</t>
 
-      <t>The MPLS IPv6 Encapsulation describes a logical link's ability
-      to exchange labeled IPv6 packets on one or more subnets.  It does
-      so by stating the interface's addresses, the corresponding prefix
-      lengths, and the corresponding labels which will be accepted fpr
-      each address.</t>
-      
       </section>
     </section>
 
@@ -1256,26 +1275,6 @@ q-->
 
   <section anchor="keepalive" title="KEEPALIVE - Layer 2 Liveness">
 
-    <t>L3DL devices SHOULD beacon frequent Layer 2 KEEPALIVE PDUs to
-    ensure session continuity.  A receiver may choose to ignore
-    KEEPALIVE PDUs.</t>
-
-    <t>An operational deployment MUST BE configured whether to use
-    KEEPALIVEs or not, either globally, or down to per-link granularity.
-    Disagreement MAY result in repeated session break and
-    reestablishment.</t>
-
-    <t>KEEPALIVEs SHOULD be beaconed at a configured frequency.  One per
-    second is the default.  Layer 3 liveness, such as BFD, may be more
-    (or less) aggressive.</t>
-
-    <t>If a KEEPALIVE is not received from a peer with which a receiver
-    has an open session for a configurable time (default 30 seconds),
-    the link SHOULD BE presumed down.  The devices MAY keep
-    configuration state and restore it without retransmission if no data
-    have changed.  Otherwise, a new session SHOULD BE established and
-    new Encapsulation PDUs exchanged.</t>
-    
 <!--
     protocol "PDU Type = 2:8,Payload Length = 0:32,Sig Type = 0:8,Signature Length = 0:16"
 -->
@@ -1292,6 +1291,31 @@ q-->
         </artwork>
       </figure>
 
+    <t>L3DL devices SHOULD beacon frequent Layer 2 KEEPALIVE PDUs to
+    ensure session continuity.  A receiver may choose to ignore
+    KEEPALIVE PDUs.</t>
+
+    <t>An operational deployment MUST BE configured whether to use
+    KEEPALIVEs or not, either globally, or down to per-link granularity.
+    Disagreement MAY result in repeated session break and
+    reestablishment.</t>
+
+    <t>KEEPALIVEs SHOULD be beaconed at a configured frequency.  One per
+    second is the default.  Layer 3 liveness, such as BFD, may be more
+    (or less) aggressive.</t>
+
+    <t>When a sender transmits a PDU which is not a KEEPALIVE, the
+    sender SHOULD reset the KEEPALIVE timer.  I.e. sending any PDU acts
+    as a keepalive.  Once the last fragment has been sent, the
+    KEEPALIVE timer SHOULD BE restarted.  Do not wait for the ACK.</t>
+
+    <t>If a KEEPALIVE or other PDUs have not been received from a peer
+    with which a receiver has an open session for a configurable time
+    (default 30 seconds), the link SHOULD BE presumed down.  The devices
+    MAY keep configuration state and restore it without retransmission
+    if no data have changed.  Otherwise, a new session SHOULD BE
+    established and new Encapsulation PDUs exchanged.</t>
+    
     </section>
 
   <section anchor="l3liveness" title="Layers 2.5 and 3 Liveness">
@@ -1303,7 +1327,7 @@ q-->
     technique.</t>
 
     <t>This protocol assumes that one or more Encapsulation addresses
-    will be used to ping, run BFD, or whatever the operator
+    may be used to ping, run BFD, or whatever the operator
     configures.</t>
 
     </section>
@@ -1317,7 +1341,7 @@ q-->
     LLEIs and Encapsulations on each logical link interface.</t>
 
     <t>Full topology discovery is not appropriate at the L3DL layer, so
-    Dijkstra à la IS-IS etc. is assumed to be done by higher level
+    Dijkstra a la IS-IS etc. is assumed to be done by higher level
     protocols such as BGP-SPF.</t>
 
     <t>Therefore the LLEIs, link Encapsulations, and state changes are
@@ -1370,24 +1394,15 @@ q-->
 
     <section anchor="dhello" title="HELLO Discussion">
 
-      <!--
-
-      <t>There is the question of whether to allow an intermediate
-      switch to be transparent to discovery.  We consider that an
-      interface on a device is a Layer 2 or a Layer 3 interface.  In
-      theory it could be a Layer 3 interface with no encapsulation or
-      Layer 3 addressing currently configured.</t>
-      -->
-
       <t>A device with multiple Layer 2 interfaces, traditionally called
       a switch, may be used to forward frames and therefore packets from
       multiple devices to one logical interface (LLEI), I, on an L3DL
       speaking device.  Interface I could discover a peer J across the
       switch.  Later, a prospective peer K could come up across the
       switch.  If I was not still sending and listening for HELLOs, the
-      potential peering with K could not be discovered.  Therefore,
+      potential peering with K could not be discovered.  Therefore, on
-      interfaces MUST continue to send HELLOs as long as they are turned
+      multi-link interfaces MUST continue to send HELLOs as long as they
-      up.</t>
+      are turned up.</t>
 
       </section>
      
@@ -1444,15 +1459,15 @@ q-->
     encapsulation, the implementation MAY mark it as primary by
     default.</t>
 
-    <t>An implementation SHOULD allow optional configuration which
+    <t>An implementation MAY allow optional configuration which updates
-    updates the local forwarding table with overlay and underlay data
+    the local forwarding table with overlay and underlay data both
-    both learned from L3DL peers and configured locally.</t>
+    learned from L3DL peers and configured locally.</t>
     
     </section>
 
   <section anchor="security" title="Security Considerations">
 
-    <t>The protocol as it is MUST NOT be used outside a datacenter or
+    <t>The protocol as is MUST NOT be used outside a datacenter or
     similarly closed environment due to lack of formal definition of the
     authentication and authorization mechanism.  Sufficient mechanisms
     may be described in separate documents.</t>
@@ -1588,12 +1603,13 @@ q-->
 
   <section anchor="acks" title="Acknowledgments">
 
-    <t>The authors thank Cristel Pelsser for multiple reviews, Jeff Haas
+    <t>The authors thank Cristel Pelsser for multiple reviews, Harsha
-    for review and comments, Joe Clarke for a useful review, John
+    Kovuru for comments during implementation, Jeff Haas for review and
-    Scudder for deeply serious review and comments, Larry Kreeger for a
+    comments, Joe Clarke for a useful review, John Scudder for deeply
-    lot of layer 2 clue, Martijn Schmidt for his contribution, Neeraj
+    serious review and comments, Larry Kreeger for a lot of layer 2
-    Malhotra for review, Russ Housley for checksum discussion and sBox,
+    clue, Martijn Schmidt for his contribution, Neeraj Malhotra for
-    and Steve Bellovin for checksum advice.</t>
+    review, Russ Housley for checksum discussion and sBox, and Steve
+    Bellovin for checksum advice.</t>
     
     </section>