Asymmetric routing is typically referred when the client to server packets take one path and server to client traffic take another path. It typically happens when there are multiple WAN links from Enterprise network to the ISP where the traffic from/to the ISP can come/go in any WAN link (packet level load balancing). It is also possible in Enterprise data centers where the machines are reachable from more than one router and servers are configured to send the packet to one router (via default gateway).
Proxy based appliances expects the full control of the connection traffic (both client to server and server to client traffic of any TCP or UDP session). If there is no asymmetric routing, these devices can be placed in line of traffic.
WCCPv2 (Web Caching Communication Protocol) can be used in cases where the routing is not symmetric. WCCP is widely implemented in routers and switches. If the routers where the asymmetric traffic is passing through, has WCCP capability, then this feature can be used to redirect the traffic to 'proxy based appliances'. WCCP feature allows routers to take traffic flow information from the WCCP client (proxy based appliances). Router then redirect the matching to the WCCP clients via GRE tunnel. WCCP also has a feature to return the traffic on GRE to the routers for further packet processing. The feature 'packet return' is optional, but in my view it is required for following reasons.
- Proxy appliances need not have sophisticated routing protocols.
- Router/switch which are redirecting the traffic can do processing on the packets in similar way whether or not the traffic is redirected, such as applying QoS policies, Firewall policies and any other processing that is configured on the router.
- Router load balancing features can be utilized on all traffic including redirected traffic. If proxy based appliance is doing its own forwarding, it may not have facility or visibility to balance the traffic across multiple WAN links.
How can the proxy appliances ensure to send the packets to the right router?
Due to asymmetric routing, for each connection there are two routers involved. One router sends the client to server traffic to Proxy appliance and second router passes server to client traffic to the appliance. Proxy appliance should ensure to the right traffic of the connection to the right router.
Proxies terminate the client initiated connections and make new connection to the server. Assuming that R1 router is sending the client traffic for a given TCP connection to the Proxy appliance and Router R2 is redirecting the traffic of TCP connection to the proxy appliance. That is, any traffic going to the client for this connection would be going through R2 and any traffic going to the actual server would be going via the router R1. So, proxy appliance when they come in picture should ensure the same behavior for the traffic. Proxy appliance is expected to keep the state and should give packets destined for client to R2 and destined to server to R1. This might require some changes to Linux Kernel TCP/IP stack or this can be implemented in IP Tables connection tracking module.
WCCPv2 protocol is documented at http://www.wrec.org/Drafts/draft-wilson-wrec-wccp-v2-00.txt.
For fear of this link vanishing in future, I have copied the text here.
INTERNET-DRAFT M CieslakD Forster
G Tiwana
R Wilson
Cisco Systems
13 Jul 2000
Expires Jan 2001
Web Cache Coordination Protocol V2.0
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.
1. Abstract
This document describes version 2.0 of the Web Cache Coordination
Protocol (WCCP). The WCCP V2.0 protocol specifies interactions between
one or more routers and one or more web-caches. The purpose of the
interaction is to establish and maintain the transparent redirection
of selected types of traffic flowing through a group of routers. The
selected traffic is redirected to a group of web-caches with the aim
of optimising resource usage and lowering response times.
The protocol does not specify any interaction between the web-caches
within a group or between a web-cache and a web-server.
2. Definitions
Assignment Method
The method by which redirected packets are distributed between
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web-caches.
Designated Web-Cache.
The web-cache in a web-cache farm responsible for dictating to the
router or routers how redirected traffic should be distributed between
the members of the farm.
Forwarding Method
The method by which redirected packets are transported from router to
web-cache.
Packet Return Method
The method by which packets redirected to a web-cache are returned to
a router for normal forwarding.
Redirection Hash Table.
A 256-bucket hash table maintained by the router or routers. This
table maps the hash index derived from a packet to be redirected to
the IP address of a destination web-cache.
Service Group
A group of one or more routers plus one or more web-caches working
together in the redirection of traffic whose characteristics are part
of the Service Group definition.
Transparent Redirection.
Transparent redirection is a technique used to deploy caching without
the need for reconfiguration of clients or servers. It involves the
interception and redirection of traffic to one or more web-caches by a
router or switch transparently to the end points of the traffic flow.
Usable Web-Cache.
From the viewpoint of a router a web-cache is considered a usable
member of a Service Group when it has sent that web-cache a
WCCP2_I_SEE_YOU message and has received in response a WCCP2_HERE_I_AM
message with a valid "Receive ID".
Web-Cache Farm.
One or more web-caches associated with a router or routers.
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3. Introduction
3.1 Protocol Overview
WCCP V2.0 defines mechanisms to allow one or more routers enabled for
transparent redirection to discover, verify, and advertise
connectivity to one or more web-caches.
Having established connectivity the routers and web-caches form
Service Groups to handle the redirection of traffic whose
characteristics are part of the Service Group definition.
The protocol provides the means to negotiate the specific method
used for load distribution among web-caches and also the method used
to transport traffic between router and cache.
A single web-cache within a Service Group is elected as the designated
web-cache. It is the responsibility of the designated web-cache to
provide routers with the data which determines how redirected traffic
is distributed between the web-caches in the Service Group.
3.2 WCCP V2.0 enhancements
WCCP V2.0 supports the following enhancements to the WCCP V1.0
protocol.
* Multi-Router Support.
WCCP V2.0 allows a farm of web-caches to be attached to more than one
router.
* Multicast Support.
WCCP V2.0 supports multicasting of protocol messages between
web-caches and routers.
* Improved Security.
WCCP V2.0 provides optional authentication of protocol packets
received by web-caches and routers.
* Support for redirection of non-HTTP traffic.
WCCP V2.0 supports the redirection of traffic other than HTTP traffic
through the concept of Service Groups.
* Packet return.
WCCP V2.0 allows a web-cache to decline to service a redirected packet
and to return it to a router to be forwarded. The method by which
packets are returned to a router is negotiable.
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* Alternative Hashing.
WCCP V2.0 allows the designated web-cache to mark individual buckets
in the Redirection Hash Table for a secondary hash. This allows the
traffic being hashed to a particular bucket to be distributed across
the members of a Service Group.
* Multiple Forwarding Methods
WCCP V2.0 allows individual web-caches to negotiate the method by
which packets are forwarded to a web-cache from a router. Packets
may now be forwarded unencapsulated using a Layer 2 destination
address rewrite.
* Multiple Assignment Methods
WCCP V2.0 allows the designated web-cache to negotiate the method by which
packets are distributed between the web-caches in a service group.
Packets may now be assigned using a hashing scheme or a masking scheme.
* Command and Status Information
WCCP V2.0 includes a mechanism to allow a web-cache to pass a command
to the routers in a Service Group. The same mechanism can be employed
by the routers to pass status information to the web-caches in a
Service Group.
4. Protocol Description
4.1 Joining a Service Group
A web-cache joins and maintains its membership of a Service Group by
transmitting a WCCP2_HERE_I_AM message to each router in the Group at
HERE_I_AM_T (10) second intervals. This may be by unicast to each
router or multicast to the configured Service Group multicast
address. The Web Cache Info component in the WCCP2_HERE_I_AM message
identifies the web-cache by IP address. The Service Info component of
the WCCP2_HERE_I_AM message identifies and describes the Service Group in
which the web-cache wishes to participate.
A router responds to a WCCP2_HERE_I_AM message with a WCCP2_I_SEE_YOU
message. If the WCCP2_HERE_I_AM message was unicast then the router will
respond immediately with a unicast WCCP2_I_SEE_YOU message. If the
WCCP2_HERE_I_AM message was multicast the router will respond via the
scheduled multicast WCCP2_I_SEE_YOU message for the Service Group.
A router responds to multicast web-cache members of a Service Group
using a multicast WCCP2_I_SEE_YOU message transmitted at 9 second
intervals with a 10% jitter.
The Router Identity component in a WCCP2_I_SEE_YOU message includes a list
of the web-caches to which the packet is addressed. A web-cache not
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in the list should discard the WCCP2_I_SEE_YOU message.
4.2 Describing a Service Group
The Service Info component of a WCCP2_HERE_I_AM message describes the
Service Group in which a web-cache wishes to participate. A Service
Group is identified by Service Type and Service ID. There are two
types of Service Group:
* Well Known Services
* Dynamic Services.
Well Known Services are known by both routers and web-caches and do
not require a description other than a Service ID.
In contrast Dynamic Services must be described to a router. A router
may be configured to participate in a particular Dynamic Service
Group, identified by Service ID, without any knowledge of the
characteristics of the traffic associated with the Service Group. The
traffic description is communicated to the router in the
WCCP2_HERE_I_AM message of the first web-cache to join the Service
Group. A web-cache describes a Dynamic Service using the Protocol,
Service Flags and Port fields of the Service Info component. Once a
Dynamic Service has been defined a router will discard any subsequent
WCCP2_HERE_I_AM message which contains a conflicting description. A
router will also discard a WCCP2_HERE_I_AM message which describes a
Service Group for which the router has not been configured.
4.3 Establishing Two-Way Connectivity
WCCP V2.0 uses a "Receive ID" to verify two-way connectivity between a
router and a web-cache. The Router Identity Info component of a
WCCP2_I_SEE_YOU message contains a "Receive ID" field. This field is
maintained separately for each Service Group and its value is
incremented each time the router sends a WCCP2_I_SEE_YOU message to
the Service Group.
The "Receive ID" sent by a router is reflected back by a web-cache in
the Web-Cache View Info component of a WCCP2_HERE_I_AM message. A
router checks the value of the "Receive ID" in each WCCP2_HERE_I_AM
message received from a Service Group member. If the value does not
match the "Receive ID" in the last WCCP2_I_SEE_YOU message sent to
that member the message is discarded.
A router considers a web-cache to be a usable member of a Service
Group only after it has sent that web-cache a WCCP2_I_SEE_YOU message
and received a WCCP2_HERE_I_AM message with a valid "Receive ID" in
response.
[Page 5]
4.4 Negotiating the Forwarding Method
A web-cache and router may negotiate the method by which packets are
forwarded to the web-cache by the router.
This negotiation is per web-cache, per Service Group. Thus web-caches
participating in the same Service Group may negotiate different
forwarding methods with the Service Group routers.
A router will advertise the supported forwarding methods for a Service
Group using the optional Capabilities Info component of the
WCCP2_I_SEE_YOU message. The absence of such an advertisement implies
the router supports the default GRE encapsulation method only.
A web-cache will inspect the forwarding method advertisement in the
first WCCP2_I_SEE_YOU message received from a router for a particular
Service Group. If the router does not advertise a method supported by
the web-cache then the web-cache will abort its attempt to join the
Service Group. Otherwise the web-cache will pick one method from those
advertised by the router and specify that in the optional Capabilities
Info component of its next WCCP2_HERE_I_AM message. Absence of a
forwarding method advertisement in a WCCP2_HERE_I_AM message implies
the cache is requesting the default GRE encapsulation method.
A router will inspect the forwarding method selected by a web-cache in
the WCCP2_HERE_I_AM message received in response to a WCCP2_I_SEE_YOU
message. If the selected method is not supported by the router the
router will ignore the WCCP2_HERE_I_AM message. If the forwarding
method is supported the router will accept the web-cache as usable and
add it to the Service Group.
4.5 Negotiating the Assignment Method
A web-cache and router may negotiate the method by which packets are
distributed between the web-caches in a Service Group.
The negotiation is per Service. Thus web-caches participating in
several Service Groups may negotiate a different assignment method for
each Service Group.
A router will advertise the supported assignment methods for a
Service Group using the optional Capabilities Info component of the
WCCP2_I_SEE_YOU message. The absence of such an advertisement implies
the router supports the default Hash assignment method only.
A web-cache will inspect the assignment method advertisement in the
first WCCP2_I_SEE_YOU message received from a router for the Service
Group. If the router does not advertise a method supported by the
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web-cache then the web-cache will abort its attempt to join the
Service Group. Otherwise the web-cache will pick one method from those
advertised by the router and specify that in the optional Capabilities
Info component of its next WCCP2_HERE_I_AM message. Absence of an
assignment method advertisement in a WCCP2_HERE_I_AM message implies
the cache is requesting the default Hash assignment method.
A router will inspect the assignment method selected by a web-cache in
the WCCP2_HERE_I_AM message received in response to a WCCP2_I_SEE_YOU
message. If the selected method is not supported by the router the
router will ignore the WCCP2_HERE_I_AM message. If the assignment
method is supported the router will accept the web-cache as usable and
add it to the Service Group.
4.5 Negotiating the Packet Return Method
A web-cache and router may negotiate the method by which packets are
returned from a web-cache to a router for normal forwarding.
The negotiation is per Service. Thus web-caches participating in
several Service Groups may negotiate a different packet return method
for each Service Group.
A router will advertise the supported packet return methods for a
Service Group using the optional Capabilities Info component of the
WCCP2_I_SEE_YOU message. The absence of such an advertisement implies
the router supports the default GRE packet return method only.
A web-cache will inspect the packet return method advertisement in the
first WCCP2_I_SEE_YOU message received from a router for the Service
Group. If the router does not advertise a method supported by the
web-cache then the web-cache will abort its attempt to join the
Service Group. Otherwise the web-cache will pick one method from those
advertised by the router and specify that method in the optional
Capabilities Info component of its next WCCP2_HERE_I_AM
message. Absence of a packet return method advertisement in a
WCCP2_HERE_I_AM message implies the cache is requesting the default
GRE packet return method.
A router will inspect the packet return method selected by a web-cache
in the WCCP2_HERE_I_AM message received in response to a
WCCP2_I_SEE_YOU message. If the selected method is not supported by
the router the router will ignore the WCCP2_HERE_I_AM message. If the
packet return method is supported the router will accept the web-cache
as usable and add it to the Service Group.
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4.6 Advertising Views of the Service Group
Each router advertises its view of a Service Group via the Router View
Info component in the WCCP2_I_SEE_YOU message it sends to web-caches.
This component includes a list of the useable web-caches in the
Service Group as seen by the router and a list of the routers in the
Service Group as reported in WCCP2_HERE_I_AM messages from
web-caches. A change number in the component is incremented if the
Service Group membership has changed since the last WCCP2_I_SEE_YOU
message sent by the router.
Each web-cache advertises its view of the Service Group via the Web
Cache View Info component in the WCCP2_HERE_I_AM message it sends to
routers in the Service Group. This component includes the list of
routers that have sent the web-cache a WCCP2_I_SEE_YOU message and a
list of web-caches learnt from the WCCP2_I_SEE_YOU messages. The Web
Cache View Info component also includes a change number which is
incremented each time Service Group membership information changes.
4.7 Security
WCCP V2.0 provides a security component in each protocol message to
allow simple authentication. Two options are supported:
* No Security (default)
* MD5 password security
MD5 password security requires that each router and web-cache wishing
to join a Service Group be configured with the Service Group
password. Each WCCP protocol packet sent by a router or web-cache for
that Service Group will contain in its security component the MD5
checksum of the WCCP protocol message (including the WCCP message
header) and a Service Group password. Each web-cache or router in the
Service Group will authenticate the security component in a received
WCCP message immediately after validating the WCCP message header.
Packets failing authentication will be discarded.
4.8 Distribution of Traffic Assignments
WCCP V2.0 allows the traffic assignment method to be negotiated. There
are two types of information to be communicated depending on the
assignment method:
* Hash Tables
* Mask/Value Sets
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4.8.1 Hash Tables
When using hash assignment each router uses a 256-bucket Redirection
Hash Table to distribute traffic for a Service Group across the member
web-caches. It is the responsibility of the Service Group's designated
web-cache to assign each router's Redirection Hash Table.
The designated web-cache uses a WCCP2_REDIRECT_ASSIGNMENT message to
assign the routers' Redirection Hash Tables. This message is
generated following a change in Service Group membership and is sent
to the same set of addresses to which the web-cache sends WCCP2_HERE_I_AM
messages. The designated web-cache will wait 1.5 HERE_I_AM_T
seconds following a change before generating the message in order to
allow the Service Group membership to stabilise.
The Redirection Hash Tables can be conveyed in either an Assignment
Info Component or an Alternate Assignment Component within a
WCCP2_REDIRECT_ASSIGNMENT. Both components contain an Assignment
Key. This will be reflected back to the designated web-cache in
subsequent WCCP2_I_SEE_YOU messages from the routers in the Service
Group. A WCCP2_REDIRECT_ASSIGNMENT may be repeated after HERE_I_AM_T
seconds if inspection of WCCP2_I_SEE_YOU messages indicates a router
has not received an assignment.
A router will flush its Redirection Hash Table if a
WCCP2_REDIRECT_ASSIGNMENT is not received within 5 HERE_I_AM_T seconds
of a Service Group membership change. A router will flush its
Redirection Hash Table if it receives a WCCP2_REDIRECT_ASSIGNMENT
message in which it is not listed.
The designated web-cache lists the web-caches to which traffic should
be distributed in either an Assignment Info Component or an Alternate
Assignment Component within a WCCP2_REDIRECT_ASSIGNMENT message. Only
those web-caches seen by every router in the Service Group are
included.
4.8.2 Mask/Value Sets
When using mask assignment each router uses masks and a table of
values to distribute traffic for a Service Group across the member
web-caches. It is the responsibility of the Service Group's designated
web-cache to assign each router's mask/value sets.
The designated web-cache uses the Alternate Assignment Component in a
WCCP2_REDIRECT_ASSIGNMENT message to assign the routers' mask/value
set. This message is generated following a change in Service Group
membership and is sent to the same set of addresses to which the
web-cache sends WCCP2_HERE_I_AM messages. The designated web-cache
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will wait 1.5 HERE_I_AM_T seconds following a change before generating
the message in order to allow the Service Group membership to
stabilise.
The Alternate Assignment Info component of the
WCCP2_REDIRECT_ASSIGNMENT contains an Assignment Key. This will be
reflected back to the designated web-cache in subsequent
WCCP2_I_SEE_YOU messages from the routers in the Service Group. A
WCCP2_REDIRECT_ASSIGNMENT message may be repeated after HERE_I_AM_T
seconds if inspection of WCCP2_I_SEE_YOU messages indicates a router
has not received an assignment.
A router will flush its mask/value set if a WCCP2_REDIRECT_ASSIGNMENT
is not received within 5 HERE_I_AM_T seconds of a Service Group
membership change. A router will flush its mask/value set if it
receives a WCCP2_REDIRECT_ASSIGNMENT in which it is not listed.
The designated web-cache lists the web-caches to which traffic should
be distributed in the Alternate Assignment Info component of the
WCCP2_REDIRECT_ASSIGNMENT message. Only those web-caches seen by every
router in the Service Group are included.
4.9 Electing the Designated Web-cache
Election of the designated web-cache will take place once a Service
Group membership has stabilised following a change. The designated
web-cache must be receiving a WCCP2_I_SEE_YOU message from every
router in the Service Group.
Election of the designated web-cache is not part of the WCCP
protocol. However it is recommended that the web-cache with the lowest
IP address is selected as designated web-cache for a Service Group.
4.10 Traffic Interception
A router will check packets passing through it against its set of
Service Group descriptions. The Service Group descriptions are
checked in priority order. A packet which matches a Service Group
description is a candidate for redirection to a web-cache in the
Service Group.
A router will not redirect a packet with a source IP address matching
any web-cache in the Service Group.
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4.11 Traffic Redirection
4.11.1 Redirection with Hash Assignment
Redirection with hash assignment is a two-stage process. In the first
stage a primary key is formed from the packet (as defined by the
Service Group description) and hashed to yield an index into the
Redirection Hash Table.
If the Redirection Hash Table entry contains an unflagged web-cache
index then the packet is redirected to that web-cache. If the bucket
is unassigned the packet is forwarded normally. If the bucket is
flagged as requiring a secondary hash then a secondary key is formed
(as defined by the Service Group description) and hashed to yield an
index into the Redirection Hash Table. If the secondary entry contains
a web-cache index then the packet is directed to that web-cache. If the
entry is unassigned the packet is forwarded normally.
4.11.2 Redirection with Mask Assignment
The first step in redirection using the mask assignment method is to
perform a bitwise AND operation between the mask from the first
mask/value set in the Service Group definition and the contents of the
packet. The output of this operation is the set of fields in the packet
which will be used for value matching. The selected fields from the
packet are then compared against each entry in the list of values for
that mask/value set. If a match is found the packet is redirected to
the web-cache associated with the value entry. If no match is found
the process is repeated for each mask/value set defined for the
Service Group. If, after trying all of the mask/value sets defined
for the Service Group, no match is found, the packet is forwarded
normally.
Mask/value sets are processed in the order in which they are
presented in the Alternate Assignment component. Value elements are
compared in the order in which they appear in the mask/value set of which
they are part.
4.12 Traffic Forwarding
WCCP allows the negotiation of the forwarding method between router
and web-cache (See Negotiating the Forwarding Method). The currently
defined forwarding methods are:
* GRE Encapsulated
* Unencapsulated with L2 rewrite
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4.12.1 Forwarding with GRE Encapsulation
Redirected packets are encapsulated in a new IP packet with a GRE [1]
header followed by a four-octet Redirect header.
The GRE encapsulation uses the simple four-octet GRE header with the
two Flags and Version octets set to zero and a Protocol Type of
0x883E.
The Redirect header is as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|D|A| Reserved | Service ID | Alt Bucket | Pri Bucket |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
D Dynamic Service
0: Well known service
1: Dynamic service
A Alternative bucket used
0: Primary bucket used
1: Alternative bucket used
Service ID
Service Group identifier
Alt Bucket
Alternative bucket index used to redirect the packet. Only valid
for hash assignment.
Pri Bucket
Primary bucket index used to redirect the packet. Only valid for hash
assignment.
4.12.2 Forwarding with L2 Rewrite
Redirected packets are not encapsulated. The router replaces the
packet's destination MAC address with the MAC address of the target
web-cache.
This forwarding method requires that the target web-cache
be directly-connected to the router at Layer 2. A router will not
allow a web-cache which is not directly attached to negotiate this
forwarding method.
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4.13 Packet Return
WCCP V2.0 allows a web-cache to decline a redirected packet and return
it to a router for normal forwarding as specified by the packet's
destination IP address. The method by which packets are returned from
router to cache is a matter for negotiation (see Negotiating the
Packet Return Method).
When a router receives a returned packet it must not attempt to
redirect that packet back to a web-cache. Two methods are available to
prevent any further redirection:
* Interface Configuration
* Encapsulation
The interface configuration method requires that a router is
configured to inhibit redirection of packets arriving over interfaces
connected to web-caches. Redirection may be disabled for all packets
arriving on an interface or for packets where the source MAC
address is that of a web-cache. This mechanism is efficient but is
topology dependant and thus may not always be suitable. In this case
the packet return method in use is L2.
The encapsulation method requires a web-cache to send returned packets
to a router with encapsulation. Returned packets are encapsulated in a
GRE packet [1] with a Protocol Type of 0x883E and contain the original
Redirect Header or a null Redirect Header if none was present in the
original redirected packet. The receiving router removes the GRE
encapsulation from the packets and forwards them without attempting to
redirect. The packet return method used in this case is GRE.
4.14 Querying Cache Time-Out
If a router does not receive a WCCP2_HERE_I_AM message from a Service
Group member for 2.5 * HERE_I_AM_T seconds it will query the member by
unicasting a WCCP2_REMOVAL_QUERY message to it. The target Service
Group member should respond by sending a series of 3 identical
WCCP2_HERE_I_AM messages, each separated by HERE_I_AM_T/10 seconds.
If a router does not receive a WCCP2_HERE_I_AM message from a Service
Group member for 3 * HERE_I_AM_T seconds it will consider the member
to be unusable and remove it from the Service Group. The web-cache
will no longer appear in the Router View Info component of the
WCCP2_I_SEE_YOU message.
The web-cache will be purged from the assignment data for the Service
Group.
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4.15 Command and Status Information
WCCP V2.0 includes a mechanism to allow web-caches to send commands to
routers within a service group. The same mechanism can be used by the
routers to provide status information to web-caches.
The mechanism is implemented by the Command Extension component. This
component is included in the WCCP2_HERE_I_AM message from a web-cache
passing commands to routers in a Service Group.
If a router needs to send status information to a web-cache it will
include a command in the Command Extension component within its own
WCCP2_I_SEE_YOU message. That command will indicate the type of status
information being carried.
5. Protocol Messages
Each WCCP protocol message is carried in a UDP packet with a
destination port of 2048. There are four WCCP V2.0 messages:
* Here I AM
* I See You
* Redirect Assign
* Removal Query
5.1 'Here I Am' Message
+--------------------------------------+
| WCCP Message Header |
+--------------------------------------+
| Security Info Component |
+--------------------------------------+
| Service Info Component |
+--------------------------------------+
| Web-Cache Identity Info Component |
+--------------------------------------+
| Web-Cache View Info Component |
+--------------------------------------+
| Capability Info Component (optional) |
+--------------------------------------+
|Command Extension Component (optional)|
+--------------------------------------+
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5.2 'I See You' Message
+--------------------------------------+
| WCCP Message Header |
+--------------------------------------+
| Security Info Component |
+--------------------------------------+
| Service Info Component |
+--------------------------------------+
| Router Identity Info Component |
+--------------------------------------+
| Router View Info Component |
+--------------------------------------+
| Assignment Info Component |
| OR |
| Assignment Map Component |
+--------------------------------------+
| Capability Info Component (optional) |
+--------------------------------------+
|Command Extension Component (optional)|
+--------------------------------------+
5.3 'Redirect Assign' Message
+--------------------------------------+
| WCCP Message Header |
+--------------------------------------+
| Security Info Component |
+--------------------------------------+
| Service Info Component |
+--------------------------------------+
| Assignment Info Component |
| OR |
| Alternate Assignment Component |
+--------------------------------------+
5.4 'Removal Query' Message
+--------------------------------------+
| WCCP Message Header |
+--------------------------------------+
| Security Info Component |
+--------------------------------------+
| Service Info Component |
+--------------------------------------+
| Router Query Info Component |
+--------------------------------------+
[Page 15]
5.5 WCCP Message Header
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
WCCP2_HERE_I_AM (10)
WCCP2_I_SEE_YOU (11)
WCCP2_REDIRECT_ASSIGN (12)
WCCP2_REMOVAL_QUERY (13)
Version
0x200
Length
Length of the WCCP message not including the WCCP Message Header.
5.6 Message Components
Each WCCP message comprises a WCCP Message Header followed by a number of
message components. The defined components are:
* Security Info
* Service Info
* Router Identity Info
* Web-Cache Identify Info
* Router View Info
* Web-Cache View Info
* Assignment Info
* Router Query Info
* Capabilities Info
* Alternate Assignment
* Assignment Map
* Command Extension
Components are padded to align on a four-octet boundary. Each
component has a 4-octet header specifying the component type and
length. Note that the length value does not include the 4-octet
component header.
[Page 16]
5.6.1 Security Info Component
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Security Option |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Security Implementation |
| . |
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
WCCP2_SECURITY_INFO (0)
Length
Length of the remainder of the component.
Security Option
WCCP2_NO_SECURITY (0)
WCCP2_MD5_SECURITY (1)
Security Implementation
If Security Option has the value WCCP2_NO_SECURITY then this field is
not present. If Security Option has the value WCCP2_MD5_SECURITY this
is a 16-octet field containing the MD5 checksum of the WCCP message and
the Service Group password. The maximum password length is 8 octets.
Prior to calculating the MD5 checksum the password should be padded
out to 8 octets with trailing zeros and the Security Implementation
field of the Security Option set to zero. The MD5 checksum is calculated
using the 8 octet padded password and the WCCP message (including the
WCCP Message Header).
[Page 17]
5.6.2 Service Info Component
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Type | Service ID | Priority | Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Port 0 | Port 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Port 6 | Port 7 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
WCCP2_SERVICE_INFO (1)
Length
Length of the remainder of the component.
Service Type
WCCP2_SERVICE_STANDARD (0).
Service is a well known service and is described by the Service ID.
All fields other than Service ID must be zero.
WCCP2_SERVICE_DYNAMIC (1).
Service is defined by the Protocol, Service Flags and Port fields.
Service ID
Service number. A number in the range 0-255. For well known services
numbers in the range 0-50 are reserved. The numbers currently defined
for well known services are:
0x00 HTTP
[Page 18]
Priority
Service priority. The lowest priority is 0, the highest is
255. Packets for redirection are matched against Services in priority
order, highest first. Well known services have a priority of 240.
Protocol
IP protocol identifier
Service Flags
0x0001 Source IP Hash
0x0002 Destination IP Hash
0x0004 Source Port Hash
0x0008 Destination Port Hash
0x0010 Ports Defined.
0x0020 Ports Source.
0x0100 Source IP Alternative Hash
0x0200 Destination IP Alternative Hash
0x0400 Source Port Alternative Hash
0x0800 Destination Port Alternative Hash
The primary hash flags (Source IP Hash, Destination IP Hash, Source
Port Hash, Destination Port Hash) determine the key which will be
hashed to yield the Redirection Hash Table primary bucket index. If
only the Destination IP Hash flag is set then the packet destination
IP address is used as the key. Otherwise if any of the primary hash
flags are set then the key is constructed by XORing the appropriate
fields from the packet with the key (which has an initial value of
zero).
The key is hashed using the following algorithm:
ulong hash = key;
hash ^= hash >> 16;
hash ^= hash >> 8;
return(hash & 0xFF);
If alternative hashing has been enabled for the primary bucket (see
Assignment Info Component) the alternate hash flags (Source IP
Alternative Hash, Destination IP Alternative Hash, Source Port
Alternative Hash, Destination Port Alternative Hash) determine the
key which will be hashed to yield a secondary bucket index. The key
is constructed by XORing the appropriate fields from the packet with
a key (which has an initial value of zero).
[Page 19]
Port 0-7
Zero terminated list of UDP or TCP port identifiers. Packets will be
matched against this set of ports if the Ports Defined flag is set. If
the Ports Source flag is set the port information refers to a source
port, if clear the port information refers to a destination port.
[Page 20]
5.6.3 Router Identity Info Component
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router ID Element |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sent To Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number Received From |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Received From Address 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Received From Address n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
WCCP2_ROUTER_ID_INFO (2)
Length
Length of the remainder of the component.
Router ID Element
Element containing the router's identifying IP address and Receive
ID. The IP address must be a valid, reachable address for the router.
Sent To Address
IP address to which the target web-cache sent the WCCP2_HERE_I_AM
message. When this component is present in a unicast WCCP2_I_SEE_YOU
message it will contain the IP address that the target web-cache
used. When present in a multicast WCCP2_I_SEE_YOU message it will
contain the Service Group multicast address.
Number Received From
The number of web-caches to which this message is directed. When using
multicast addressing it may be less than the number of caches which
[Page 21]
actually see the message.
Received From Address 0-n
List of the IP addresses of web-caches to which this message is
directed. When using multicast addressing it may be a subset of the
caches which actually see the message.
[Page 22]
5.6.4 Web-Cache Identity Info Component
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Web-Cache Identity Element |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
WCCP2_WC_ID_INFO (3)
Length
Length of the remainder of the component.
Web-Cache Identity Element
Element containing the web-cache IP address and Redirection Hash Table
mapping.
[Page 23]
5.6.5 Router View Info Component
This represents a router's view of the Service Group.
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Member Change Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Assignment Key |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Routers |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Web-Caches |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Web-Cache Identity Element 0 |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Web-Cache Identity Element n |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
WCCP2_RTR_VIEW_INFO (4)
Length
Length of the remainder of the component.
Member Change Number
Incremented each time there is a change in Service Group membership.
[Page 24]
Assignment Key
Assignment Key element received in the last WCCP2_REDIRECT_ASSIGNMENT
message. Used by the designated web-cache to verify that an assignment
has been executed.
Number of Routers
Number of routers in the Service Group
Router 0-n
IP addresses of routers in the Service Group. This list is constructed
from routers reported by web-caches via WCCP2_HERE_I_AM messages. Note
that a router does not include itself in the list unless it has also
been reported via a WCCP2_HERE_I_AM message.
Number of Web-Caches
Number of useable web-caches in the Service Group
Web-Cache Identity Element 0-n
Identity elements of useable web-caches in Service Group. This list
contains web-caches that have sent the router a WCCP2_HERE_I_AM
message with a valid "Received ID".
[Page 25]
5.6.6 Web Cache View Info Component
This represents a web-cache's view of the Service Group.
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Change Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Routers |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router ID Element 0 |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router ID Element n |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Web-Caches |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Web Cache address 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Web Cache address n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
WCCP2_WC_VIEW_INFO (5)
Length
Length of the remainder of the component.
Change Number
Incremented each time there is a change in the view.
Number of Routers
Number of routers in the Service Group
[Page 26]
Router ID Element 0-n
List of elements containing the identifying IP address for each router
in the Service Group and the last "Received ID" from each.
Number of Web-Caches
Number of web-caches in the Service Group
Web Cache address 0-n
List of web-cache IP addresses learnt from WCCP2_I_SEE_YOU messages.
[Page 27]
5.6.7 Assignment Info Component
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Assignment Key |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Routers |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router Assignment Element 0 |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router Assignment Element n |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Web-Caches |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Web-Cache 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Web-Cache n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bucket 0 | Bucket 1 | Bucket 2 | Bucket 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bucket 252 | Bucket 253 | Bucket 254 | Bucket 255 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
WCCP2_REDIRECT_ASSIGNMENT (6)
Length
Length of the remainder of the component.
[Page 28]
Assignment Key
The designated web-cache expects this element to be returned by a router
in subsequent WCCP2_I_SEE_YOU messages.
Number of Routers
Number of routers reachable by the designated web-cache.
Router Assignment Element 0-n
Elements containing the router IP address, "Receive ID" and "Change
Number" for each router.
Number of Web-Caches
Number of useable web-caches in the Service Group seen by all routers.
Web Cache 0-n
List of the IP addresses of useable web-caches in Service Group. The
position of a web-cache identifier in this list is the web-cache
index. The first entry in the list has an index of zero.
Bucket 0-255
Contents of the Redirection Hash Table. The content of each bucket is a
web-cache index value in the range 0-31. If set the A flag indicates
that alternative hashing should be used for this web-cache. The value
0xFF indicates no web-cache has been assigned to the bucket.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Index |A|
+-+-+-+-+-+-+-+-+
[Page 29]
5.6.8 Router Query Info Component
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receive ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sent To IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Target IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
WCCP2_QUERY_INFO (7)
Length
Length of the remainder of the component.
Router ID
Router IP address. The same address advertised in a WCCP2_I_SEE_YOU
message.
Receive ID
Receive ID expected by the router.
Sent To IP Address
IP address to which the web-cache sent its last WCCP2_HERE_I_AM
message. This will not be the Router ID if the web-cache is
multicasting its WCCP2_HERE_I_AM messages.
Target IP Address
IP address of web-cache being queried.
[Page 30]
5.6.9 Capabilities Info Component
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Capability Element 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Capability Element n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
WCCP2_CAPABILITY_INFO (8)
Length
Length of the remainder of the component.
Capability Element
Element in Type-Length-Value format (TLV) describing a router or
web-cache capability.
[Page 31]
5.6.10 Alternate Assignment Component
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Assignment Type | Assignment Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Assignment Body |
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
WCCP2_ALT_ASSIGNMENT (13)
Length
Length of the remainder of the component.
Assignment Type
Currently defined values:
WCCP2_HASH_ASSIGNMENT (0x00)
WCCP2_MASK_ASSIGNMENT (0x01)
Assignment Length
Length of Assignment Body
Assignment Body
The format of Assignment Body depends upon the value of Assignment Type.
Assignment Type = WCCP2_HASH_ASSIGNMENT
In this case the body of the message is identical to the Assignment
Info Component with the Type and Length fields omitted.
[Page 32]
Assignment Type = WCCP2_MASK_ASSIGNMENT
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Assignment Key |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Routers |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router Assignment Element 0 |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router Assignment Element n |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Mask/Value Set Elements (m) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask/Value Set Element 0 |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask/Value Set Element m |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Assignment Key
The designated web-cache expects this element to be returned by a
router in subsequent WCCP2_I_SEE_YOU messages.
Number of Routers
Number of routers reachable by the designated web-cache.
Router Assignment Element 0-n
Element containing the router IP address, Receive ID and Change
Number for each router.
Number of Mask/Value Set Elements (m)
Number of Mask/Value Set elements in this message
[Page 33]
Mask/Value Set Element 0-m
A list of the Mask/Value Element Sets for the Service Group
[Page 34]
5.6.11 Assignment Map Component
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Mask/Value Set Elements (n) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask/Value Set Element 0 |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask/Value Set Element n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
WCCP2_ASSIGN_MAP (14)
Length
Length of the remainder of the component.
Number of Mask/Value Set Elements (n)
Number of Mask/Value Set elements in the message
Mask/Value Set Element 0-n
A list of the Mask/Value Element Sets for the Service Group
[Page 35]
5.6.12 Command Extension Component
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Command Type | Command Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Command Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
WCCP2_COMMAND_EXTENSION (15)
Length
Length of the remainder of the component.
Command Type
The command specifier.
Command Length
The length of the Command Data field of this command
The defined Command Types are:
Command Type: WCCP2_COMMAND_TYPE_SHUTDOWN (01)
Command Length: 4
Command Data: Web-cache IP address
Description: This command is used by a web-cache to indicate to
the routers in a Service Group that it is shutting
down and should no longer receive any redirected traffic.
Command Type: WCCP2_COMMAND_TYPE_SHUTDOWN_RESPONSE (02)
Command Length: 4
Command Data: Web-cache IP address.
Description: This command is used by a router to acknowledge
receipt of a SHUTDOWN command received from the web-cache
identified by the IP address in the Command Data field.
[Page 36]
5.7 Information Elements
5.7.1 Router ID Element
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receive ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Router ID
Router's identifying IP address. This must be a valid IP address by
which the router is reachable.
Receive ID
Defined per Service Group. Incremented each time the router sends a WCCP
protocol message including a Router Identity Info component. Will never be
zero.
5.7.2 Web-Cache Identity Element
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| WC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hash Revision |U| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bucket Block 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bucket Block 7 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Assignment Weight | Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
WC Address
Web-Cache IP address
[Page 37]
Hash Revision
0x00
U
If set indicates that the web cache does not have an assignment in the
Redirection Hash Table and that Bucket Block data is historical.
Historical data may be used by the designated web-cache to re-assign
the same bucket set to a web-cache that left and subsequently
rejoined a Service Group.
Bucket Block 0-7
256-bit vector. A set bit indicates the corresponding Redirection
Hash Table bucket is assigned to this web-cache.
Assignment Weight
Hash weight. May be used to indicate to the designated web-cache how new
assignments should be made.
Status
Hash status. May be used to indicate to the designated web-cache how new
assignments should be made.
5.7.3 Assignment Key Element
This element identifies a particular assignment.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key Change Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Key IP Address
Designated web-cache IP address
Key Change Number
Incremented if a change has occurred.
[Page 38]
5.7.4 Router Assignment Element
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receive ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Change Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Router ID
Router's identifying IP address. It must be a valid address by which
the router is reachable.
Receive ID
Last Receive ID received from the router identified by Router
ID. A router will ignore an assignment if Receive ID is invalid.
Change Number
Last Member Change Number received from the router identified by
Router ID. A router will ignore an assignment if Change Number is
invalid.
5.7.5 Capability Element
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
Currently defined types are:
WCCP2_FORWARDING_METHOD 0x01
WCCP2_ASSIGNMENT_METHOD 0x02
WCCP2_PACKET_RETURN_METHOD 0x03
[Page 39]
Length
Length of Capability element Value
Value
The length and format of the value field is dependant on the capability type.
Type = WCCP2_FORWARDING_METHOD
A 32-bit bitmask indicating supported/selected forwarding methods.
Currently defined values are:
WCCP2_FORWARDING_METHOD_GRE 0x00000001
WCCP2_FORWARDING_METHOD_L2 0x00000002
Type = WCCP2_ASSIGNMENT_METHOD
A 32-bit bitmask indicating supported/selected assignment methods.
Currently defined values are:
WCCP2_ASSIGNMENT_METHOD_HASH 0x00000001
WCCP2_ASSIGNEMNT_METHOD_MASK 0x00000002
Type = WCCP2_PACKET_RETURN_METHOD
A 32-bit bitmask indicating supported/selected packet return methods.
Currently defined values are:
WCCP2_PACKET_RETURN_METHOD_GRE 0x00000001
WCCP2_PACKET_RETURN_METHOD_L2 0x00000002
5.7.6 Mask/Value Set Element
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask Element |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Value Elements (n) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value Element 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value Element n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Mask Element
Mask element for this set.
Number of Value Elements (n)
The number of value elements in this set.
Value Element 0-n
The list of value elements for this set.
5.7.7 Mask Element
Note that in all of the mask fields of this element a zero means
"Don't care".
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Address Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port Mask | Destination Port Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Source Address Mask
The 32 bit mask to be applied to the source IP address of the packet.
Destination Address Mask
The 32 bit mask to be applied to the destination IP address of the packet.
Source Port Mask
The 16 bit mask to be applied to the TCP/UDP source port field of the packet.
Destination Port Mask
The 16 bit mask to be applied to the TCP/UDP destination port field of the packet.
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5.7.8 Value Element
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Address Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port Value | Destination Port Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Web Cache IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Source Address Value
The value to match against the source IP address of the packet after
masking.
Destination Address Value
The value to match against the destination IP address of the packet after
masking.
Source Port Value
The value to match against the TCP/UDP source port number of the
packet after masking.
Destination Port Value
The value to match against the TCP/UDP destination port number of the
packet after masking.
Web-cache IP address
The IP address of the web-cache to which packets matching this value
element should be sent.
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6. Security Considerations
WCCP V2 provides a mechanism for message authentication. It is
described in section 4.7 of this document. The authentication
mechanism relies on a password known to all routers and web-caches in
a Service Group. The password is part of the Service Group
configuration and is used to compute message checksums which can be
verified by other members of the group. Should the password become
known to a host attempting to disrupt the operation of a Service Group
it would be possible for that host to spoof WCCP messages and appear
as either a router or web-cache in the Service Group.
To pose as a router in a Service Group a host would advertise its
presence to the members of the group in I_SEE_YOU messages. If
accepted as part of the Service Group the host would receive the
configuration for the group in a HERE_I_AM message from the designated
web-cache. This situation would not pose any threat to the operation
of the Service Group because the host would not be performing any
packet redirection and all packets would flow normally.
To pose as a web-cache within a Service Group a host would advertise
its presence in HERE_I_AM messages. Acceptance of the host as part of
the Service Group would be decided by the designated cache and may be
subject to additional security checks not specified by WCCP. Should
the host become part of the Service Group it would be assigned a
proportion of the traffic redirected by the routers in the Service
Group. Assuming that the host drops any redirected packets the net
effect to clients would be that some attempts to retrieve content via
the Service Group routers would fail.
7. References
[1] Hanks, Li, Farinacci & Traina, "Generic Routing Encapsulation
(GRE)", RFC 1701, October 1994
8. Authors' Addresses
Martin Cieslak
Cisco Systems
170 Tasman Drive
San Jose, CA 95143
David Forster
Cisco Systems
170 Tasman Drive
San Jose, CA 95143
[Page 43]
Gurumukh Tiwana
Cisco Systems
170 Tasman Drive
San Jose, CA 95143
Rob Wilson
Cisco Systems
170 Tasman Drive
San Jose, CA 95143
email: robewils@cisco.com
Expires January 2001
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