Table Of Contents
Microsoft Point-to-Point Compression (MPPC)
Configure the Interface to Perform MPPC
MPPC BRI Interface Configuration Example
MPPC Asynchronous Interface Configuration Example
MPPC Serial and Virtual Template Interface Configuration Example
Microsoft Point-to-Point Compression (MPPC)
Feature Summary
Microsoft Point-to-Point Compression (MPPC) is a scheme used to compress Point-to-Point Protocol (PPP) packets between Cisco and Microsoft client devices. The MPPC algorithm is designed to optimize bandwidth utilization in order to support multiple simultaneous connections. The MPPC algorithm uses a Lempel-Ziv (LZ) based algorithm with a continuous history buffer, called a dictionary.
The Compression Control Protocol (CCP) configuration option for MPPC is 18.
Exactly one MPPC datagram is encapsulated in the PPP information field. The PPP protocol field indicates the hexadecimal type of 00FD for all compressed datagrams. The maximum length of the MPPC datagram transmitted over PPP is the same as the MTU of the PPP interface; however this length cannot be greater than 8192 bytes since the history buffer is limited to 8192 bytes. If compressing the data results in data expansion, the original data is sent as an uncompressed MPPC packet.
The history buffers between compressor and decompressor are synchronized by maintaining 12 bit coherency count. If the decompressor detects that the coherency count is out of sequence, then the error recovery process begins and is described through the following steps:
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Reset Request (RR) packet sent from the decompressor.
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Synchronization is achieved without CCP using the Reset Acknowledge (RA) packet that can be additionally time-consuming.
Compression negotiation between a router and a Windows 95 client occurs through the following steps:
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Benefits
MPPC provides the following benefits:
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Note
List of Terms
acknowledgment (ACK)—A notification sent from one network device to another to acknowledge that some event (receipt of a message, for example) has occurred. Usually abbreviated as ACK.
Compression Control Protocol (CCP)—A protocol that provides a defined method of negotiating data compression over the Point-to-Point Protocol (PPP).
Lempel-Ziv algorithm (LZ)—A compression algorithm, based on a dynamically encoded dictionary, that replaces a continuous stream of characters with codes. The symbols represented by the codes are stored in memory in a dictionary-style list. LZ-style compression is used in a number of compression algorithms, such as Stacker (STAC) compression. In contrast, statistical compression methods use a fixed and, oftentimes, a non-adaptive encoding method, which is best used where data is consistent and predictable.
Link Control Protocol (LCP)—A protocol that establishes, configures, and tests data link connections used by PPP.
Multilink PPP (MLP)—A protocol that allows packets to be fragmented, whereby the fragments can be simultaneously sent over multiple point-to-point links to the same remote address. MLP provides bandwidth on demand and reduces transmission latency across WAN links.
negative acknowledgment (NAK)—A response sent from a receiving device to a sending device indicating that the information received contained errors. Typically abbreviated as NAK.
Point-to-Point Protocol (PPP)—A protocol that encapsulates network layer protocol information over point-to-point links. The RFC for PPP is RFC 1661.
Stacker compression (STAC)—A data compression algorithm developed by STAC Electronics that is based on the LZ compression algorithm. Although effective, the STAC compression algorithm uses more CPU resources to perform compression. Cisco IOS software uses an optimized version of STAC compression.
Virtual Private Dial-Up Network (VPDN)—A networking service that allows separate and autonomous protocol domains to share common access infrastructure including modems, access servers, and ISDN routers. VPDN uses the Layer 2 Forwarding protocol (L2F) which permits the tunneling of link level frames.
Restrictions
The following restrictions apply to the MPPC feature:
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Platforms
This feature is supported on these platforms:
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Prerequisites
PPP encapsulation must be enabled. For information on how to configure PPP encapsulation refer to the Cisco IOS Release 11.3 Dial Solutions Configuration Guide.
Supported MIBs and RFCs
This feature supports the following RFC:
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No MIBs are supported by this feature.
Configuration Task
Once the router is configured for PPP encapsulation, you can configure the interface to perform MPPC as described in the following section.
Configure the Interface to Perform MPPC
There is only one command required to configure MPPC. The existing compress command now supports the mppc keyword, which prepares the interface to initiate CCP and negotiates MPPC with the Microsoft client. To configure MPPC on the interface, perform the following task in interface configuration mode:
The ignore-pfc keyword instructs the router to ignore the protocol field compression flag negotiated by LCP. For example, the uncompressed standard protocol field value for IP is 0x0021 and 0x21 when compression is enabled. When the ignore-pfc option is enabled, the router will continue to use the uncompressed value (0x0021). Using the ignore-pfc option is helpful for some asynchronous driver devices which use an uncompressed protocol field (0x0021), even though the pfc is negotiated between peers. displays protocol rejections when the debug ppp negotiation command is enabled. These errors can be remedied by setting the ignore-pfc option.
Figure 1 Sample Debug PPP Negotiation Showing Protocol Reject
PPP Async2: protocol reject received for protocol = 0x2145PPP Async2: protocol reject received for protocol = 0x2145PPP Async2: protocol reject received for protocol = 0x2145Configuration Examples
This section provides the following examples:
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MPPC BRI Interface Configuration Example
The following example configures BRI interface 0 to perform MPPC:
interface BRI0ip unnumbered ethernet0encapsulation pppisdn spid1 5551234dialer map ip 172.21.71.74 5551234dialer-group 1compress mppcMPPC Asynchronous Interface Configuration Example
The following example configures asynchronous interface 1 to implement MPPC and ignore the protocol field compression flag negotiated by LCP:
interface async1ip unnumbered ethernet0encapsulation pppasync default routingasync dynamic routingasync mode interactivepeer default ip address 172.21.71.74compress mppc ignore-pfcMPPC Serial and Virtual Template Interface Configuration Example
The following example creates a virtual access interface (virtual-template interface 1) and serial interface 0, which is configured for X.25 encapsulation. MPPC values are configured on the virtual-template interface and will ignore the negotiated protocol field compression flag.
interface ethernet0ip address 172.20.30.102 255.255.255.0!interface virtual-template1ip unnumbered ethernet0peer default ip address pool vtemp1compress mppc ignore-pfc!interface serial0no ipaddressno ip mroute-cacheencapsulaiton x25x25 win 7x25 winout 7x25 ips 512x25 ops 512clock rate 50000!ip local pool vtemp1 172.20.30.103 172.20.30.104ip route 0.0.0.0 0.0.0.0 172.20.30.1!translate x25 31320000000000 virtual-template 1Command Reference
This section documents the modified compress command. The compress command is revised to add the mppc keyword that supports compression for Microsoft clients, such as Windows 95 and Windows NT. Only the information that applies to the mppc keyword is provided. Refer to the Cisco IOS Release 11.3 Dial Solutions Command Reference for other keywords available with the compress command.
compress mppc
To configure software compression for PPP encapsulation, use the compress interface configuration command. To disable compression on the interface, use the no form of this command.
compress [mppc [ignore-pfc]]
no compress [mppc [ignore-pfc]]Syntax Description
mppc
Specifies that the MPPC compression algorithm will be used.
ignore-pfc
(Optional) Specifies that the protocol field compression flag negotiated through LCP will be ignored.
Default
PPP compression is disabled.
Command Mode
Interface configuration
Usage Guidelines
This command first appeared in Cisco IOS Release 11.3 T.
The compress mppc command is used for point-to-point connections between Cisco and Microsoft clients.
PPP encapsulation supports predictor, STAC LZS-DCP, and MPPC compression algorithms.
Compression is a means of optimizing traffic by running a data set through specific algorithms that either reduce space or bandwidth required to transmit the data set. Some algorithms reduce packet header size while others condense data within packets.
MPPC implements an LZ based compression algorithm that uses a compression dictionary to compress PPP packets connecting to Microsoft clients.
Compression is performed in software and may significantly affect system performance. We recommend that you disable compression if CPU load exceeds 65 percent. To display the CPU load, use the show process cpu EXEC command.
Both end-point devices must be configured to use the same compression method (predictor, Stacker or MPPC).
If the majority of your traffic is already compressed files, we recommend that you not use compression. If the files are already compressed, the additional processing time spent in attempting unsuccessfully to compress them again will slow system performance.
Example
The following example configures asynchronous interface 0 to perform MPPC compression and ignore the protocol field compression flag:
interface async0encapsulation pppcompress mppc ignore-pfcRelated Commands
show compress
show process cpuDebug Commands
The debug ppp command is revised to add the mppc keyword that supports compression for Microsoft clients such, as Windows 95 and Windows NT. Only the information that applies to debug ppp mppc is provided. Refer to the Cisco IOS Release 11.3 Debug Command Reference for complete debug ppp information.
debug ppp
Use the debug ppp EXEC command with the mppc keyword to display information specific to the exchange of PPP connections using MPPC. To disable debugging output, use the no form of this command.
debug ppp mppc
[no] debug ppp mppcSyntax Description
mppc
Causes the debug ppp command to display decompressed MPPC header compression information for incoming packets.
Usage Guidelines
Use this command to debug PPP connections on point-to-point links using MPPC.
This command is useful for obtaining incorrect packet sequence number information where MPPC compression is enabled.
The debug ppp command currently exists; only the mppc keyword is added to support MPPC.
Refer to the Cisco IOS Release 11.3 Debug Command Reference for other keywords available with the debug ppp command.
CautionThe debug ppp mppc command is CPU intensive and should be used with caution. This command should be disabled immediately after debugging.
Sample Display
shows a typical PPP packet exchange between the router and Microsoft client where the MPPC header sequence numbers increment correctly.Sample Debug PPP MPPC Output
Router# debug ppp mppcMPPC Decomp. :mppc_hdr = 0x2027,hdr->coherency_count = 39, coherency_count = 39MPPC Decomp. :mppc_hdr = 0x2028,hdr->coherency_count = 40, coherency_count = 40MPPC Decomp. :mppc_hdr = 0x2029,hdr->coherency_count = 41, coherency_count = 41describes the fields for the debug ppp mppc output.1
shows the output from debug ppp negotiation and debug ppp error commands which can be used to troubleshoot initial ppp negotiation and setup errors. This example shows a virtual interface (virtual interface 1) during normal PPP operation and CCP negotiation. Refer to the Cisco IOS Release 11.3 Debug Command Reference for details and field descriptions about these debug commands.
Figure 2 Sample Debug PPP Negotiation and Debug PPP Errors Output
Router# debug ppp nego errorVt1 PPP: Unsupported or un-negotiated protocol. Link arpVPDN: Chap authentication succeeded for p5200Vi1 PPP: Phase is DOWN, SetupVi1 VPDN: Virtual interface created for dinesh@cisco.comVi1 VPDN: Set to Async interfaceVi1 PPP: Phase is DOWN, SetupVi1 VPDN: Clone from Vtemplate 1 filterPPP=0 blockingVi1 CCP: Re-Syncing history using legacy method%LINK-3-UPDOWN: Interface Virtual-Access1, changed state to upVi1 PPP: Treating connection as a dedicated lineVi1 PPP: Phase is ESTABLISHING, Active OpenVi1 LCP: O CONFREQ [Closed] id 1 len 25Vi1 LCP: ACCM 0x000A0000 (0x0206000A0000)Vi1 LCP: AuthProto CHAP (0x0305C22305)Vi1 LCP: MagicNumber 0x000FB69F (0x0506000FB69F)Vi1 LCP: PFC (0x0702)Vi1 LCP: ACFC (0x0802)Vi1 VPDN: Bind interface direction=2Vi1 PPP: Treating connection as a dedicated lineVi1 LCP: I FORCED CONFREQ len 21Vi1 LCP: ACCM 0x000A0000 (0x0206000A0000)Vi1 LCP: AuthProto CHAP (0x0305C22305)Vi1 LCP: MagicNumber 0x12A5E4B5 (0x050612A5E4B5)Vi1 LCP: PFC (0x0702)Vi1 LCP: ACFC (0x0802)Vi1 VPDN: PPP LCP accepted sent & rcv CONFACKVi1 PPP: Phase is AUTHENTICATING, by this endVi1 CHAP: O CHALLENGE id 1 len 27 from "l_4000"Vi1 CHAP: I RESPONSE id 20 len 37 from "dinesh@cisco.com"Vi1 CHAP: O SUCCESS id 20 len 4Vi1 PPP: Phase is UPVi1 IPCP: O CONFREQ [Closed] id 1 len 10Vi1 IPCP: Address 15.2.2.3 (0x03060F020203)Vi1 CCP: O CONFREQ [Not negotiated] id 1 len 10Vi1 CCP: MS-PPC supported bits 0x00000001 (0x120600000001)Vi1 IPCP: I CONFREQ [REQsent] id 1 len 34Vi1 IPCP: Address 0.0.0.0 (0x030600000000)Vi1 IPCP: PrimaryDNS 0.0.0.0 (0x810600000000)Vi1 IPCP: PrimaryWINS 0.0.0.0 (0x820600000000)Vi1 IPCP: SecondaryDNS 0.0.0.0 (0x830600000000)Vi1 IPCP: SecondaryWINS 0.0.0.0 (0x840600000000)Vi1 IPCP: Using the default poolVi1 IPCP: Pool returned 11.2.2.5Vi1 IPCP: O CONFREJ [REQsent] id 1 len 16Vi1 IPCP: PrimaryWINS 0.0.0.0 (0x820600000000)Vi1 IPCP: SecondaryWINS 0.0.0.0 (0x840600000000)Vi1 CCP: I CONFREQ [REQsent] id 1 len 15Vi1 CCP: MS-PPC supported bits 0x00000001 (0x120600000001)Vi1 CCP: Stacker history 1 check mode EXTENDED (0x1105000104)Vi1 CCP: Already accepted another CCP option, rejecting this STACKERVi1 CCP: O CONFREJ [REQsent] id 1 len 9Vi1 CCP: Stacker history 1 check mode EXTENDED (0x1105000104)Vi1 IPCP: I CONFACK [REQsent] id 1 len 10Vi1 IPCP: Address 15.2.2.3 (0x03060F020203)Vi1 CCP: I CONFACK [REQsent] id 1 len 10Vi1 CCP: MS-PPC supported bits 0x00000001 (0x120600000001)Vi1 CCP: I CONFREQ [ACKrcvd] id 2 len 10Vi1 CCP: MS-PPC supported bits 0x00000001 (0x120600000001)Vi1 CCP: O CONFACK [ACKrcvd] id 2 len 10Vi1 CCP: MS-PPC supported bits 0x00000001 (0x120600000001)Vi1 CCP: State is OpenVi1 IPCP: I CONFREQ [ACKrcvd] id 2 len 22Vi1 IPCP: Address 0.0.0.0 (0x030600000000)Vi1 IPCP: PrimaryDNS 0.0.0.0 (0x810600000000)Vi1 IPCP: SecondaryDNS 0.0.0.0 (0x830600000000)Vi1 IPCP: O CONFNAK [ACKrcvd] id 2 len 22Vi1 IPCP: Address 11.2.2.5 (0x03060B020205)Vi1 IPCP: PrimaryDNS 171.69.1.148 (0x8106AB450194)Vi1 IPCP: SecondaryDNS 171.69.2.132 (0x8306AB450284)Vi1 IPCP: I CONFREQ [ACKrcvd] id 3 len 22Vi1 IPCP: Address 11.2.2.5 (0x03060B020205)Vi1 IPCP: PrimaryDNS 171.69.1.148 (0x8106AB450194)Vi1 IPCP: SecondaryDNS 171.69.2.132 (0x8306AB450284)Vi1 IPCP: O CONFACK [ACKrcvd] id 3 len 22Vi1 IPCP: Address 11.2.2.5 (0x03060B020205)Vi1 IPCP: PrimaryDNS 171.69.1.148 (0x8106AB450194)Vi1 IPCP: SecondaryDNS 171.69.2.132 (0x8306AB450284)Vi1 IPCP: State is OpenVi1 IPCP: Install route to 11.2.2.5
