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Protocol Compliance Statements for the CSG 3.1(3)C7(1)

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Protocol Compliance Statements for the CSG 3.1(3)C7(1)

Table Of Contents

Protocol Compliance Statements for the CSG 3.1(3)C7(1)

Layer 4 Inspection (accounting type=other)

Layer 7 Inspection (accounting type=specific protocol)


Protocol Compliance Statements for the CSG 3.1(3)C7(1)


This appendix provides protocol compliance statements for the CSG 3.1(3)C7(1). Any RFCs that are not explicitly listed are not supported.

Layer 4 Inspection (accounting type=other)

The Cisco Content Services Gateway (CSG) differentiates TCP and User Datagram Protocol (UDP), and classifies all other protocols simply as IP. All protocols can be billed as TCP, UDP, or IP if further protocol-specific processing is not needed (or if deeper inspection for such protocols is not supported).

IP—Compliant with RFC 791. To avoid leakage, the CSG drops packets on a service for a prepaid user while reconciling the user's quota for that service. The frequency depends on how quickly the user is consuming quota on that service and generally amounts to a few packets. This is controlled by setting the CSG_BASIS_BYTE_RESERVED_MAX variable up to a setting of 256000. Settings above this value have no effect.

The CSG volume counters wrap at 0xFFFFFFFF (268435455 bytes). The volume counters are 32 bits unsigned.

The CSG supports IP fragmentation for generic Layer 4 flows, regardless of protocol and regardless of the order in which the flows arrive

UDP—Compliant with RFC 768.

TCP—Compliant with standard TCP (RFC 3168).

Layer 7 Inspection (accounting type=specific protocol)

IP—Compliant with RFC 791.

The CSG supports IP fragmentation for HTTP; Internet Message Application Protocol, version 4 (IMAP4); Post Office Protocol version 3 (POP3); Simple Mail Transfer Protocol (SMTP); Wireless Application Protocol (WAP) 2.0; and WAP 1.x, regardless of the order in which the flows arrive. The CSG does not support IP fragmentation for FTP, for Real Time Streaming Protocol (RTSP) control connections, or for RADIUS flows. The CSG drops IP fragments for those unsupported protocols.

The CSG volume counters wrap at 0xFFFFFFFF (268435455 bytes). The volume counters are 32 bits unsigned.

UDP—Compliant with RFC 768.

See the Layer 7 Inspection "IP" bullet for further restrictions.

TCP—Compliant with standard TCP (RFC 793), with the following exception:

When performing Layer 7 inspection of TCP-based protocols, the CSG buffers packets that are received out of order and processes them in the proper order. This does not guarantee that the CSG transmits the packets in any specific order, only that the CSG can handle them arriving out of order.

See the Layer 7 Inspection "IP" bullet for further restrictions.

WP-TCP—Compliant with mandatory elements of Wireless Profiled TCP (WP-TCP) (WAP-225-TCP-20010331-a at http://www.wapforum.org/what/technical.htm), with the exception of selective acknowledgment (SACK) (RFC 2018).

Impact: End-user latency for lossy transmissions.

See the Layer  Inspection "TCP" bullet for further restrictions.

HTTP—Compliant with RFC 1945 (HTTP 1.0) and RFC 2616 (HTTP 1.1), with the following exceptions:

1. Each HTTP method must be initiated by the same endpoint that initiated the TCP connection (that is, by the same side that sent the TCP SYN).

Impact: Client requests transfer no data (that is, the requests hang). See the "TO-TCP" sub-bullet under the Layer 7 Inspection "MMS for WAP 2.0" bullet for an example.

2. The maximum HTTP transaction volume is 268435455 bytes. If this length is exceeded, the CSG invokes Layer 4 billing for the remainder of the connection.

3. HTTP request parsing is limited to 64000 bytes.

Impact: Any headers beyond this limit are not recognized and therefore are not used in matching URL or header maps.

4. The CSG supports up to 65535 concurrent HTTP TCP connections.

5. If the HTTP server or client causes improper parsing, the CSG reverts to Layer 4 billing for the remainder of the TCP connection. Examples of improper parsing include:

- If an HTTP response does not begin with "HTTP", the CSG increments a Layer 7 error statistic, "HTTP invalid msgs", and invokes Layer 4 billing. (The CSG requires that all HTTP responses begin with the string "HTTP".)

- If a response contains characters other than ASCII decimal digits (0x30 through 0x39), the CSG increments the "HTTP invalid msgs" statistic and invokes Layer 4 billing. (When parsing the response for an HTTP return code, the CSG accepts only ASCII decimal digits.)

- If the CSG cannot parse the status line in the response, it invokes Layer 4 billing for all subsequent traffic.

6. HTTP status 101 (switching protocols) is not supported. The CSG expects all subsequent requests to be unencrypted and parsable by HTTP rules (see the Layer 7 Inspection "HTTPS" bullet for further restrictions).

Impact: The user TCP connection might hang until the content idle timer expires or until the connection closes for some other reason.

7. Error codes 204, 205, and 304 do not require a body. If a response contains one of these error codes, the CSG ignores "Content-Type:", "Content-Length:", and "Transfer-Encoding:chunked" headers that might be present in error.

8. The CSG does not support the CLOSING or TIME-WAIT states for TCP connections. After the end-points exchange FIN_ACK messages, the connection is terminated immediately, and the CSG does not process any out-of-order packets for the connection.

9. The CSG does not pass TCP header options when it performs HTTP deep packet inspection (accounting type http), other than Maximum Segment Size (MSS) header options.

10. The existence of an HTTP HEAD method in a persistent HTTP TCP connection causes the CSG to invoke Layer 4 billing for the remainder of the connection. This Layer 4 charging is reported via the HTTP statistics CDR for the Connect transaction. The CSG will not discern any additional transactions after the Head method is detected. If a method map is configured for the Connect method, the traffic is charged against the matching policy. If no policy exists with the method map, the CSG passes the traffic without charge.

11. An HTTP message that has a "Content-Type:" header, but no "Content-Length:" or "Transfer-Encoding:chunked" header, causes the CSG to invoke Layer 4 billing.

12. If there are multiple responses for one request, the CSG invokes Layer 4 billing.

13. Multipart content is supported. The CSG supports the standard "RANGE" header as well as the earlier "byterange" directive on the URI. In both cases, the "Content-Type: multipart..." header must be present in order for the CSG to consider the stream for multipart parsing. The particular subtype in the header does not matter, as long as multipart is specified as the type. If multipart is not specified in the "Content-Type:" header, the CSG parses the data as regular HTTP and reverts to Layer 4 billing if any errors in the format are detected.

Compliant with RFC 2774 (HTTP Extension Framework), subject to the restrictions above.

See the Layer  Inspection "TCP" bullet for further restrictions.

HTTPS—Because HTTPS URLs and other headers are encrypted, the CSG cannot provide Layer 7 information for HTTPS requests.

Also, switching from HTTP to HTTPS within the same persistent connection is subject to the following restrictions:

Switching via the Connect method (RFC 2817) is supported. The CSG detects the Connect method and invokes Layer 4 billing for the remainder of the TCP connection. This Layer 4 charging is reported via the HTTP statistics CDR for the Connect transaction. The CSG will not discern any additional transactions after the Connect method is detected. If a method map is configured for the Connect method, the traffic is charged against the matching policy. If no policy exists with the method map, the CSG passes the traffic without charge.

Switching via the "Upgrade" header (RFC 2817) is ignored. The CSG attempts to parse the traffic as normal HTTP. When parsing fails, the CSG invokes Layer 4 billing for all subsequent traffic on the TCP connection, charging against the last matching policy.

See the Layer 7 Inspection "HTTP" bullet for further restrictions.

WAP 2.0 (HTTP over WP-TCP transport)—The CSG supports the billing of WAP 2.0 over clear text HTTP and the differential billing of Multimedia Messaging Service (MMS) over WAP 2.0 over clear text HTTP (see the Layer 7 Inspection "MMS for WAP 2.0" for details) as specified by the WAP Forum, with the following exceptions:

There are two variants of Push Over the Air-HTTP (OTA-HTTP): Terminal-Originated TCP (TO-TCP) and Push Proxy Gateway-Originated TCP (PO-TCP). The CSG does not support TO-TCP, as described in WAP-235-PushOTA-20010425-a, for flows billed at Layer 7 (that is, those with HTTP policies). PO-TCP can be configured, but it requires more complex configuration (see the Layer 7 Inspection "MMS for WAP 2.0" bullet for details).

The CSG cannot bill Transport Layer Security (TLS) (encrypted connections) as WAP 2.0 flows. In WAP-235-PushOTA-20010425-a, TLS is referenced as OTA-HTTP-TLS.

See the Layer 7 Inspection "HTTPS" bullet for restrictions on switching from HTTP to HTTPS within the same persistent connection. WAP-219-TLS-20010411-a specifies that only the Connect method is supported (that is, portions of RFC 2817 pertaining to Upgrade requests or responses are not supported by WAP 2.0 clients).

Because the CSG does not currently pass TCP options, the CSG does not support the WAP-GW-STD-11, WAP-GW-STD-13, WAP-GW-STD-14, WAP-GW-STD-15, and WAP-GW-STD-17 standards.

See the Layer 7 Inspection "HTTP 1.1," "HTTPS," and "WP-TCP" bullets for further restrictions.

MMS for WAP 2.0 (HTTP transport)—At present the Multimedia Messaging Service (MMS) standard is very incomplete.

For MMS differentiation, the CSG requires that the "Content-Type" header in the request be set to "application/vnd.wap.mms-message" on all MMS, WAP 2.0, and HTTP exchanges, except for message retrieval requests.

For message retrieval, the "Content-Type" header is not present in the GET request, so the CSG uses the URL in the GET request and ignores the "Content-Type" header in the response. This method provides reasonable differentiation, although examining the "Content-Type" in the response is the preferred technique for MMS differentiation, in accordance with the standard.

MMS over WAP 2.0 allows three types of notification:

1. Short Message Service (SMS) notification carrying the Uniform Resource Identifier (URI) for the MMS. The handset then initiates a GET request to that URI to retrieve the information.

2. TO-TCP, which starts with SMS but provides only the IP address of the Push Proxy Gateway (PPG). The terminal must then open a TCP connection and wait for an HTTP request from the PPG. This HTTP request is an OPTIONS method and must succeed before the handset can retrieve the notification.

3. PO-TCP, which is similar to TO-TCP, except the TCP connection is opened by the PPG and is followed by the OPTIONS method.

The CSG Layer 7 billing for MMS relies entirely on notification types 1 and 3. The CSG does not support TO-TCP. If a terminal reuses a persistent PO-TCP to initiate a new method request, the packets are dropped and the PO-TCP connection appears to be hung until the TCP retry attempts expire.

See the Layer 7 Inspection "WAP 2.0" bullet for further restrictions.

POP3—Compliant with RFC 1939. The CSG reports the RFC 2822 (Internet Message Format) headers in the body of the POP3 message.

See the Layer  Inspection "TCP" bullet for further restrictions.

IMAP4—Compliant with RFC 3501.

See the Layer  Inspection "TCP" bullet for further restrictions.

SMTP—Compliant with RFC 2821. Reports headers in the SMTP are body formatted in accordance with RFC 2822 - Internet Message Format.

The CSG does not support SMTP command pipelining as defined in RFC 2920 - SMTP Service Extension for Command Pipelining.

Impact: Everything is charged for the first e-mail, and incomplete or no SMTP envelopes and RFC 2822 headers are reported (depending on the e-mail content).

See the Layer  Inspection "TCP" bullet for further restrictions.

FTP—Compliant with RFC 959. The CSG requires that the control connection use port 21 on the server.

See the Layer  Inspection "TCP" bullet for further restrictions.

RTSP—Compliant with RFC 2326, except that the RFC allows RTSP control flows on either TCP or UDP, but the CSG supports RTSP control flows only on TCP. The CSG requires that the control connection use port 554 on the server, even though some servers allow other ports to be used. The CSG does not parse Synchronized Multimedia Integration Language (SMIL) or Streaming Data Protocol (SDP) files, so correlation is not supported across multiple elements in the file.

For Interleaved RTSP (in which Control and Stream both share the control connection), and for RTSP over HTTP:554 (with policy of type=rtsp), the CSG parses only the first SETUP command.

See the Layer  Inspection "TCP" bullet for further restrictions.

WAP 1.x (WSP/WTP) —Compliant with the following specifications:

1. WAP-100, Wireless Application Protocol Architecture Specification (WAP-100-WAPArch-19980430-a)

2. WAP-165, Push Architectural Overview (WAP-165-PushArchOverview-19991108-a)

3. WAP-203, Wireless Session Protocol Specification (WAP-203-WSP-20000504-a)

4. WAP-201, Wireless Transaction Protocol Specification (WAP-201-WTP-20000219-a)

MMS for Wireless Session Protocol (WSP) is identified via WSP Content Type value 0X3E or via an application/vnd.wap.mms-message.

See the Layer 7 Inspection "UDP" bullet for further restrictions.

RADIUS—Compliant with RFC 2865 and RFC 2866. The CSG can inspect RADIUS Access and RADIUS Accounting messages.

For RADIUS inspection, the CSG does not support fragmented RADIUS messages or messages that exceed an Ethernet frame size (approximately 1470 bytes). Also, the CSG does not police the attributes that it does not use.

Specific to RFC 2865—Base RADIUS specification:

In order to parse information in the Access-Accept message (from the real server), the CSG requires attribute 1 (User-Name) or 31 (Calling-Station-Id), as configured. Page 63 of RFC 2865 shows a summary of the attributes for each of the RADIUS messages. It shows that attribute 31 is not included in the RADIUS Access-Accept message, while Attribute 1 can be. The description of attribute 31 says, "It is only used in Access-Request packets." There is no mention of MUST/SHALL/etc.

For VSA subattribute parsing, we require the String contents to be encoded as a sequence of vendor type / vendor length / value fields. This is a recommendation (SHOULD) on page 48 of RFC 2865. If subattribute parsing is not configured, this restriction does not apply.

Specific to RFC 2866—Accounting:

When operating as a RADIUS Accounting Endpoint, the RADIUS Accounting-Response generated by the CSG does not include any attributes, as per page 9 of the RFC:

"A RADIUS Accounting-Response is not required to have any attributes in it."

However, on page 5, step 3, of the RFC:

"The remote server logs the accounting-request (if desired), copies all Proxy-State attributes in order and unmodified from the request to the response packet, and sends the accounting-response to the forwarding server."

The CSG is not compliant with this latter statement, though it is not clear if this is a required element of the RFC.

Specific to RFC 2882—Extended practices:

The CSG supports the RADIUS Disconnect messages defined in this RFC:

40 Disconnect Request

41 Disconnect Ack

42 Disconnect Nak

Specific to RFC 3576—Dynamic extensions:

This RFC notes specific ports to which the Disconnect Request is to be sent. The CSG allows the customer to configure the NAS port. Also, note specific actions to be taken when the Ack or Nak is received—The CSG uses the Ack or Nak only to determine whether it is to send the Request. The CSG does not use, process, or report any attributes included in the Ack or Nak. Attributes that the CSG sends in the Request are defined by the customer.

The CSG does not support any other message types in this RFC.

See the Layer 7 Inspection "UDP" bullet for further restrictions.