Internet DRAFT - draft-forster-wrec-wccp-v1

draft-forster-wrec-wccp-v1









INTERNET-DRAFT                                         M Cieslak
<draft-forster-wrec-wccp-v1-00.txt>                    D Forster
                                                       Cisco Systems
                                                       7 July 2000
                                                       Expires January 2001

                  Web Cache Coordination Protocol V1.0

Status of this Memo

   This document is an Internet-Draft and is in full conformance with all
   provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering Task
   Force (IETF), its areas, and its working groups. Note that other
   groups may also distribute working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time. It is inappropriate to use Internet-Drafts as reference material
   or to cite them other than as "work in progress".

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/lid-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html

   Cisco has a patent pending that may relate to WCCP V1.0. If any
   patents issue to Cisco or its subsidiaries with claims that are
   necessary for practicing WCCP V1.0, then any party will be able to
   obtain a license from Cisco to use any such patent claims under openly
   specified, reasonable, non-discriminatory terms to implement WCCP
   V1.0. No license is required for nonprofit institutions.

Abstract

   This draft documents the Web Cache Coordination Protocol (WCCP)
   V1.0. This protocol is used (a) to associate a single router with one
   or more web-caches for the purposes of transparent redirection of HTTP
   traffic, and (b) to allow one of the web-caches to dictate how the
   router distributes transparently-redirected traffic across the
   associated web-caches.

   This draft describes the interactions between a router and one or more
   web-caches. It does not describe the interactions between a group of
   associated web-caches or those between a web-cache and a web-server.




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Definitions

   Transparent Redirection.

      Transparent redirection is a technique used to deploy web-caching
      without the need for reconfiguration of web-clients. It involves the
      interception and redirection of HTTP traffic to one or more web-caches
      by a router or switch, transparently to the web-client.

   Web-Cache Farm.

      One or more web-caches associated with a router.

   Designated Web-Cache.

      The web-cache in a web-cache farm responsible for dictating to the
      router how redirected traffic should be distributed across the members
      of the farm.

   Redirection Hash Table.

      A 256-bucket hash table maintained by the router. This table maps the
      IP destination address of a packet for redirection to the IP address
      of a web-cache in the farm

Description of Protocol

   WCCP has two main functions. The first is to allow a router enabled
   for transparent redirection to discover, verify, and advertise
   connectivity to one or more web-caches.

   The second function is to allow one of the web-caches, the designated
   web-cache, to dictate how the router distributes redirected traffic
   across the web-cache farm.

   It is recommended that the web-cache with the lowest IP address is
   elected as designated web-cache for a farm.

Discovery

   WCCP V1.0 allows a single router to be associated with one or more
   web-caches. A group of web-caches associated with a router is referred
   to as a web-cache farm. A web-cache may be directly attached to the
   router or some hops distant.

Joining a web-cache farm

   A web-cache joins a web-cache farm by periodically unicasting a



                                                               [Page 2]

   WCCP_HERE_I_AM packet to the router associated with the farm at
   intervals of HERE_I_AM_T (10) seconds. The source IP address of the
   WCCP_HERE_I_AM uniquely identifies the web-cache. The router unicasts
   a WCCP_I_SEE_YOU packet back to the web-cache in response to each
   WCCP_HERE_I_AM it receives.

Verifying connectivity

   The Received_ID fields in the WCCP_HERE_I_AM and WCCP_I_SEE_YOU
   packets are used to verify two-way connectivity between the router and
   web-cache. The router increments the value of the Received_ID field
   each time it sends a WCCP_I_SEE_YOU to a web-cache and expects to
   receive the same value back in the Received_ID field of the next
   WCCP_HERE_I_AM from that cache. WCCP_HERE_I_AM packets containing an
   invalid Received_ID are ignored.

   The Received_ID in the initial WCCP_HERE_I_AM sent from a web-cache is
   ignored. The router will only consider a web-cache to be reachable
   when it has received a subsequent WCCP_HERE_I_AM with a correct
   Received_ID. Note that a useable web-cache is merely reachable; the
   router will not redirect traffic to a newly-acquired useable web-cache
   until instructed to do so in a WCCP_ASSIGN_BUCKETS packet from the
   designated web-cache.

Advertising connectivity

   The router includes a list of the web-caches it considers to be usable
   in each WCCP_I_SEE_YOU packet it transmits. Each entry in the list
   includes the IP address of the web-cache and indicates which buckets
   in the Redirection Hash Table are currently assigned to that
   web-cache. This information is provided for the benefit of the
   designated web-cache.

   A Change ID in the WCCP_I_SEE_YOU packet is incremented whenever the
   web-cache list changes or the bucket allocation for an entry in the
   list is modified.

Timing-out a web-cache

   If the router does not receive a valid WCCP_HERE_I_AM for 3 *
   HERE_I_AM_T seconds it will no longer consider a web-cache to be
   useable. In this case the web-cache is no longer advertised in the
   WCCP_I_SEE_YOU packet and all buckets previously assigned to the
   web-cache in the router's Redirection Hash Table are marked as
   unassigned.






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Assignment

   The router associated with a web-cache farm distributes redirected
   traffic by destination IP address across the members of the farm as
   directed by the designated web-cache via the WCCP_ASSIGN_BUCKETS
   packet.

   How the designated web-cache arrives at the traffic distribution
   described by the WCCP_ASSIGN_BUCKETS packet is outside the scope of
   this draft.

   Since the router has no knowledge of the designated web-cache election
   process it will accept a WCCP_ASSIGN_BUCKETS packet from any member of
   the web-cache farm.

   The value of the Received_ID in the WCCP_ASSIGN_BUCKETS packet must
   match that in the last WCCP_I_SEE_YOU sent to the designated
   web-cache. If the Received_ID is not valid the router will ignore the
   WCCP_ASSIGN_BUCKETS packet.

   On receipt of a valid WCCP_ASSIGN_BUCKETS packet the router will set
   its Redirection Hash Table from information contained in the
   packet. This information comprises a list of web-caches followed by a
   256-bucket hash table. The position of a web-cache in the list is its
   index number, the index number of the first entry being zero. Each
   bucket in the hash table may contain the value 0xFF, indicating no
   web-cache has been assigned to that bucket, or the index number of a
   web-cache.

   The router does not generate a packet in response to the
   WCCP_ASSIGN_BUCKET. However the change in the Redirection Hash Table
   will be reflected in subsequent WCCP_I_SEE_YOU packets generated by
   the router.

Packet Redirection

Detection

   The router detects HTTP packets (TCP packets with a destination port
   number of 80) and redirects them to a web-cache in the web-cache farm.

   The destination IP address of a candidate packet is hashed to yield an
   index into the 256-bucket Redirection Hash Table. The indexed bucket
   indicates to which web-cache the packet should be redirected. If the
   bucket in the Redirection Hash Table is unassigned the packet cannot
   be redirected and should be forwarded normally.





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Encapsulation

   Each redirected packet is encapsulated in a GRE packet[1]. The
   encapsulation uses the base four-octet GRE header with the two Flags
   and version octets set to zero and a Protocol Type of 0x883E.

   An encapsulated packet may be fragmented if it exceeds the output
   interface's MTU.

Returned packets

   The router must ensure that HTTP traffic passing through it from
   members of the web-cache farm en-route to a web-server is not
   redirected.

   The router will not redirect any packet with a source address
   belonging to a member of the web-cache farm.


































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Format of Protocol Packets

   This section defines the format of the WCCP packets.

   Each WCCP protocol packet is carried in a UDP packet with a
   destination port of 2048

Here I Am

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              Type                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Protocol Version                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Hash Revision                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Hash Information (0)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            .                                  |
   |                            .                                  |
   |                            .                                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Hash Information (7)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |U|                         Reserved                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Received ID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      WCCP_HERE_I_AM (7)

   Protocol Version

      4

   Hash Revision

      0

   Hash Information

      A 256-element bit-vector. A set bit indicates that the corresponding
      bucket in the Redirection Hash Table is assigned to this web-cache.
      Normally the value of the Hash Information present in the last



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      WCCP_I_SEE_YOU message received by this cache. In the initial
      WCCP_HERE_I_AM sent to the router it may be zero or the value assigned
      to the cache in a previous membership of this web-cache farm. This
      information may be used by the designated web-cache to re-assign
      buckets to the cache.

   U

      Normally the value of the U flag present in the last WCCP_I_SEE_YOU
      message received by this cache. Set in first WCCP_HERE_I_AM to
      indicate that Hash Information is historical.

   Received ID

      The value of the Received ID present in the last WCCP_I_SEE_YOU
      received by this web-cache.



































                                                               [Page 7]

I See You

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Type                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Protocol Version                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Change Number                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Received ID                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Number of WCs                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Web-Cache List Entry(0)                    |
   |                            .                                  |
   |                            .                                  |
   |                            .                                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Web-Cache List Entry(n)                    |
   |                            .                                  |
   |                            .                                  |
   |                            .                                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      WCCP_I_SEE_YOU (8)

   Protocol Version

      4

   Change Number

      Incremented if a Web-Cache List Entry has been added, removed or its
      hash information has been modified since the last WCCP_I_SEE_YOU sent
      by the router.

   Received ID

      Incremented each time the router generates a WCCP_I_SEE_YOU. Will
      never be zero.

   Number of WCs

      Number of Web-Cache List Entry elements in the packet.



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Web-Cache List Entry

   The Web-Cache List Entry describes a Web-Cache by IP Address and lists
   the redirection hash table entries assigned to it.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         IP Address                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Hash Revision                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Hash Information (0)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            .                                  |
   |                            .                                  |
   |                            .                                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Hash Information (7)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |U|                         Reserved                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   IP Address

      Web-cache IP Address

   Hash Revision

      0

   Hash Information

      A 256-element bit-vector. A set bit indicates that the corresponding
      bucket in the Redirection Hash Table is assigned to this web-cache.

   U

      If set indicates web-cache is not assigned in the Redirection Hash
      Table and that the web-cache hash information is historical. This
      information may be used by the designated web-cache to reassign
      buckets to a web-cache which has rejoined the farm.









                                                               [Page 9]

Assign Bucket

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Type                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Received ID                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Number of Web Caches                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Web-Cache 0 IP Address                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             .                                 |
   |                             .                                 |
   |                             .                                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Web-Cache n IP Address                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Bucket 0    |   Bucket 1    |   Bucket 2    |   Bucket 3    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             .                                 |
   |                             .                                 |
   |                             .                                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Bucket 252  |   Bucket 253  |   Bucket 254  |   Bucket 255  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      WCCP_ASSIGN_BUCKET (9)

   Received ID

      Value of Received ID in last WCCP_I_SEE_YOU received from router.

   Number of Web Caches

      Number of Web Caches to which redirect traffic can be sent.

   Web-Cache IP Address, 0-n

      IP Addresses of Web-Caches to which redirect traffic can be sent. The
      position of a Web-Cache's IP Address in this list is the Web-Cache's
      index number. The first entry in the list has an index number of zero.

   Bucket 0-255




                                                              [Page 10]

      These 256 buckets represent the redirection hash table. The value of
      each bucket may be 0xFF (Unassigned) or a Web-Cache index number
      (0-31).

References

   [1] Hanks, Li, Farinacci & Traina, "Generic Routing Encapsulation
   (GRE)", RFC 1701, October 1994

Authors' Addresses

   Martin Cieslak
   Cisco Systems
   170 Tasman Drive
   San Jose, CA 95143

   David Forster
   Cisco Systems
   170 Tasman Drive
   San Jose, CA 95143

   Phone: +44-208-7568967
   Email: dforster@cisco.com


   Expires January 2001

























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