Network Working Group S. Venaas Internet-Draft UNINETT Intended status: Informational H. Santos Expires:
January 10,May 22, 2008 July 9,NEC Europe Ltd. November 19, 2007 ssmping Protocol draft-ietf-mboned-ssmping-01draft-ietf-mboned-ssmping-02 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 10,May 22, 2008. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract The ssmping is a tool that is used to checkprotocol specified in this document allows for checking whether one can receive SSM,multicast, both Source-Specific Multicast (SSM) and Any-Source Multicast (ASM), as well as obtaining someto obtain additional multicast related information. This protocol is based on an implementation of tools called ssmping requires both a clientand a server supporting the ssmping protocol to work. We here specify this protocol.asmping. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 . Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Protocol specification . . . . . . . . . . . . . . . . . . . . 4 3.1. Option format . . . . . . . . . . . . . . . . . . . . . . 5 3.2. Defined Options . . . . . . . . . . . . . . . . . . . . . 5 4. Packet Format . . . . . . . . . . . . . . . . . . . . . . . . 78 5. Message types and options . . . . . . . . . . . . . . . . . . 9 6. Client Behaviour . . . . . . . . . . . . . . . . . . . . . . . 10 7. Server Behaviour . . . . . . . . . . . . . . . . . . . . . . . 11 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8 6.12 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 7.13 10. Security Considerations . . . . . . . . . . . . . . . . . . . 8 8.13 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 8.1.13 11.1. Normative References . . . . . . . . . . . . . . . . . . . 9 8.2.13 11.2. Informative References . . . . . . . . . . . . . . . . . . 913 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 913 Intellectual Property and Copyright Statements . . . . . . . . . . 1015 1. Introduction The ssmping is a tool that is designed to allow a local host to check whether it is able to receive aprotocol specified in this document allows for checking multicast connectivity. Not only reception of multicast flow(SSM by default,or ASM when specific options are used) originated by a remote host. Additionally it is able to reportASM), but can also provide other information such as the amount of time used to establish thelike multicast tree,tree setup time, the number of hops the flow'spackets have traveledtraveled, as well as the packet delay and loss. This functionality resemblesresembles, in partpart, the ICMP Echo Request/ Reply infrastructureRequest/Reply infrastructure, but overuses UDP and implemented byrequires both the ssmpinga client and server.a server implementing this protocol. The protocol here specified is based on the actual implementation of the ssmping tooland asmping tools  which isare widely used by the Internet community to conduct multicast connectivity tests. 2. Architecture Before going intodescribing the protocol detailsin detail, we will describeprovide a brief overview of how it isthe protocol may be used and what information it may provide. The typical usage of an ssmpingssmping/asmping session is as follows. A server runs continuously in orderto serve requestrequests from clients. When a hostuser decides to verify the multicast reception from a specific server (knowing one of the server's unicast addresses is required), the ssmpingclient joins an SSM channel (S,G) where S iswill send a unicast address ofmessage to the targetserver and G is the standard multicast group definedasking for use by ssmping. Aftera group to use. Optionally the user may have requested a specific group or scope, in which case the client will ask for a group matching the user's request. The server will respond with a group to use, or an error if no group is available. Next, the client joins an SSM channel (S,G) where S is a unicast address of the target server, or an ASM group G, where G is the group specified by the server. After joining the channel, the client sendsunicasts ssmping requests encapsulated into the server. The requests are sent using UDP with destination port set to the standardised ssmping port and the unicast address of the server.[TBD]. The requests are sent periodically, e.g.e.g., once per second, to the server. The requests contain a serialsequence number, and typically a timestamp. The requests are typically, but not necessarily always, simplyechoed back by the server.server, except the server may add a few options. To each request, the server sends two replies. One as unicast back to the port and address the request was sourcedsent from, and also one as multicast back to the port the request came from. It is currently left openfrom which portthe request is sourced from, whether this port should be standardised or not.originated with the requested group G as destination address. The server should specify the TTL or Hop Limit ofused for both the replies are setunicast and multicast messages (we recommend at least 64) and includes a TTL option for the client to 64.compute the number of hops. The client should leave the SSM channelchannel/group when it has finished its measurements. By use of this protocol, a client can obtain information onabout several aspects of themulticast quality. First of all,delivery characteristics. First, by receiving unicast replies, it can verify that the server is receiving the unicast requests, is operational and responding. HenceHence, provided that the client receives unicast replies, a failure in receivingto receive multicast indicates either a multicast problem or a multicast administrative restriction. If it does receive multicast, it knows not only that it can receive; it may also estimate the amount of time it took to establish the multicast tree (at least if it is in the range of seconds), whether there are packet drops, and the length and variation of round trip timesRound Trip Times (RTT). For unicastunicast, the RTT is the time from when the unicast request is sent to when the reply is received. The measured multicast RTT also references the client's unicast request. SinceBy use of the server setsTTL or Hop Limit to 64, itoption specifying the TTL of the replies when they are originated, the client can also knowdetermine the number of router hops it is awayfrom the source. By obtaining the same values bySince similar information is obtained in the unicast replies, the host may compare its multicast and unicast results and is able to check for differences in the number of hops, RTT, etc. Provided that the server sends the unicast and multicast replies nearly simultaneously, it may also be able to measure the difference in one way delay for unicast and multicast on the path from server to client, and also differences in delay variation.delay. Servers may optionally specify a timestamp. This may be useful since the unicast and multicast replies can not be sent simultaneously (the delay depending on the host's operating system and load), or whenwhether the client and server have synchronised clocks. 3. Protocol specification TheThere are four different ssmping requestsmessage types. There are Echo Request and replies haveEcho Reply messages used for the actual measurements; there is an Init message that SHOULD be used to initialise a ping session and negotiate which group to use; and finally a Server Response message that is mainly used in response to the Init message. The ssmping messages share a common format,format: one octet specifying the message type, followed by a number of options in TLV (Type, Length and Value) format. This makes the protocol easily extendible. Generally the client includesThe Init message generally contains some prefix options asking the server for a numbergroup from one of the specified prefixes. The server responds with a Server Response message that contains the group address to use, or possibly prefix options indescribing what multicast groups the request,server may be able to provide. For an Echo Request the client generally includes a number of options, and a server may simply echo the content back (only changing the message type), without inspecting the options. However, the server SHOULD add a TTL option, and there are a number ofsome other options that a server implementation mayMAY support, wheree.g., the client may ask for acertain information or a specific behaviour from the server. In some cases the server will need to add options in the response.The response will thenEcho Replies (one unicast and one multicast) MUST first contain the exact options from the request,request (in the same order), and then right after those,then, immediately following, options appended by the server. This document defines a number of different options. Some options don'tdo not require processing by servers and are simply returned unmodified in the reply. There are howeverare, however, other client options that the server may care about, and also server options that may be requested by a client. Generally a simple client will only include a few options, and get exactly the same options and values echoed back. Strictly speaking the protocol could work without any options. The protocol here defined does not require the use of any options, and a client may operate without specifying any. However some of the options allow the client to obtain additional information.Unless otherwise specified, an option MUST NOT be used multiple times in a request. Also unless otherwise specified, an option MUST NOT be appended by the server multiple times. Note that some options, like timestamp, may be added by both the client and the server. In that case the timestamp option would be in the response twice. But as said above, it is not used multiple times in the request, and not appended multiple times bythe server.same message. 3.1. Option format All options are TLVs formatted as specified below. 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 (2 octets) specifies the option. The different options are defined below. Length (2 octets) specifies the length of the value field. Depending on the option typetype, it can be from 0 to 65535. Value. The value must always be of the specified length. See the respective option definitions for possible values. If the length is 0, the value field is not included. 3.2. Defined Options Version, type 0. Length MUST be 1. This option MUST always be included in all messages, and the value MUST be set to 2 (in decimal). Note that there are older implementations of ssmping that only partly follow this specification. They can be regarded as version 1 and do not use this option. Client Identifier,ID, type 1. Length MUST be non-zero. Only used by clients.A client SHOULD always include this.this option in all messages (both Init and Request). The client may use any value it likes to be able to detect whether a reply is a reply to this queryInit/Request or not. A server should treat this as opaque data, and simply leave it unchanged in the reply.reply (both Server Response and Reply). The value might be a process ID, perhaps process ID combined with an IP address because it may receive multicastedmulticast responses to queries from other clients. It is left to the client implementor how to make use of this.this option. Sequence number, type 2. Length MUST be 4. Only used by clients.A client SHOULDMUST always include this in Request messages and MUST NOT include this.it in Init messages. A server replying to a Request message MUST copy it into the Reply (or Server Response message on error). This contains a 32 bit sequence number. The values would typically start at 1 and increase by one for each request in a sequence. Timestamp, type 3. Length MUST be 8 bytes. A client SHOULD include this.this in Request messages and MUST NOT include it in Init messages. A server MAY support this. If supportedreplying to a request MUST copy it into the Reply. In addition, a server supporting this option, SHOULD be includedinclude it in the replyReply messages, if requested by the client. Note that this means that the option may be present in the Reply message twice; both a client timestamp as part of the echoed Request, and another timestamp added by the server. The timestamp specifies the time when the message (query or reply) is sent. The first 4 bytes specify the number of seconds since the Epoch (beginning of the year 1970). The next 4 bytes specify the number of microseconds since the last second since the Epoch. Multicast group, type 4. Length MUST be greater than 1. It is optional for clients and serversMAY be used in Server Response messages to support this. It allows atell the client to specify whichwhat group the server should send to. This is currentlyto use in subsequent Request messages. It MUST be used by a tool called "asmping"in Request messages to test ASM connectivity. Thetell the server may have restrictions on which groups canwhat group address to respond to (this group would typically be used.previously obtained in a Server Response message). It MUST be used in Reply messages (copied from the Request message). It MUST NOT be used in Init messages. The format of the option value is as below. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AddrAddress Family | Multicast group address... | +-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ .... | The address family is a value 0-1270-65535 as assigned by IANA for Internet Address Families . This is followed by the group address. For IPv4 the option value length will be 5,6, for IPv6 17.18. Option Request Option, type 5. Length MUST be greater than 1. TheThis option MAY be used in Init and Request messages. It MUST NOT be used in any other messages, except that a server will, in a Reply, echo back this option if present in the Request. This option contains a list of option types offor options that the client requestsis requesting from the server. SupportingSupport for this option is optional for both clients and servers. The length of this option will be a non-zero even number, since it contains one or more option types that eachare two octets.octets each. The format of the option value is as below. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Type | Option Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ..... | The value might contain an odd number of options, including just one.This option might be used by the client to ask the server to include options like timestampTimestamp or version. Version, type 6. Length MUST be non-zero. Supporting this option is optional.Server Information. A server supporting this option SHOULD add it if andclient MAY request Server Information in Init messages; it MUST NOT request it in other messages. A client MAY request a Timestamp in Request messages; it MUST NOT request it in other messages. Server Information, type 6. Length MUST be non-zero. It MAY be used in Server Response messages and MUST NOT be used in other messages. Support for this option is optional. A server supporting this option SHOULD add it in Server Response messages if and only if requested by the client. The value is just unformatted texta UTF-8 string that might contain vendor and version information for the server implementation. It may also contain information on which options the server supports. An interactive client MAY support this option, and SHOULD then allow a user to request this string and display it. Type 7, Reserved. This option code value was used by early implementations for an option that nowis now deprecated. This option should no longer be used. Clients MUST not use this option, and Servers MUST ignore it. Pad, type 8. Length can be anything, including 0. This option is used by clients to increase the request sizessize in order to gethave the server deliver responses of a particular size. If the server adds any options when responding, it shouldshould, if possible make the response the same size as the request by shrinking the pad option (i.e., not simply including itit, as is, like forall other client options). If the options added by the server consume as much space as the pad option does, or more, the server should remove the entire pad option. 4. Packet Format The formatTTL, type 9. Length MUST be 1. This option contains a single octet specifying the TTL of a Reply message. Every time a server sends a unicast or multicast Reply message, it SHOULD include this option specifying the TTL. This is used by clients to determine the number of hops the ssmpingmessages have traversed. It MUST NOT be used in other messages. Although this option is not absolutely required, the server is expected to use it if it knows what the TTL of the Reply will be. In general the server can specify a one octet message type, followed byspecific TTL to the host stack. Multicast prefix, type 10. Length MUST be greater than 2. It MAY be used in Init messages to request a variable number of options.group within the prefix(es), it MAY be used in Server Response messages to tell the client what prefix(es) it may try to obtain a group from. It MUST NOT be used in Request/Reply messages. 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 | Option | +-+-+-+-+-+-+-+-+ . | | . | | . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option | | . | | .Address Family | Prefix Length |Partial address| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ .... | .The address family is a value 0-65535 as assigned by IANA for Internet Address Families . This is followed by a prefix length (0-32 for IPv4, 0-128 for IPv6), and finally a group address. The group address need only contain enough octets to cover the prefix length bits (e.g., there need be no group address if the prefix length is 0, the group address would have to be 3 octets long if the prefix length is 17-24). Any bits past the prefix length MUST be ignored. For IPv4 the option value length will be 3-7, while for IPv6 3-19. Session ID, type 11. Length MUST be non-zero. A server MAY include this in Server Response and Reply messages. If a client receives this option in a message, the client MUST echo the Session ID option in Reply messages, with the exact same value, until the next message is received from the server. If the next message from the server has no Session ID or a new Session ID value, the client should do the same, either not use the Session ID, or use the new value. 4. Packet Format The format of all messages is a one octet message type, directly followed by a variable number of options. 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 | Option | +-+-+-+-+-+-+-+-+ . | | . | | . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option | | . | | . | | . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option | | . | | . | | . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ There are twofour message types defined. Type 81 (the character Q in ASCII) specifies a query.an Echo Request (Query). Type 65 (the character A in ASCII) specifies an Echo Response (Answer). Type 73 (the character I in ASCII) is an Init message, and type 83 (the character S in ACII) is a Server Response message. The options directly follow the type octet and are not aligned in any way (no spacing or padding), i.e., options might start at any octet boundary. The option format is specified above. 5. Message types and options For the readers convenience we provide the matrix below, showing what options can go in what messages. Option / Message Type | Init | Server Response | Request | Reply | -----------------------------------------------------------------+ Version (0) | MUST | MUST | MUST | ECHO | Client ID (1) |SHOULD| ECHO | SHOULD | ECHO | Sequence number (2) | NOT | ECHO | MUST | ECHO | Timestamp (3) | NOT | NOT | SHOULD |ECHO/RQ| Multicast group (4) | NOT | MAY | MUST | ECHO | Option Request (5) | MAY | NOT | MAY | ECHO | Server Information (6)| NOT | RQ | NOT | NOT | Reserved (7) | NOT | NOT | NOT | NOT | Pad (8) | NOT | NOT | MAY | ECHO* | TTL (9) | NOT | NOT | NOT |SHOULD | Multicast prefix (10) | MAY | MAY | NOT | NOT | Session ID (11) | NOT | MAY | ECHO | MAY | NOT means that the option MUST NOT be included. ECHO for a server means that if the option is specified by the client, then the server MUST echo the option back in the response, with the exact same option value. The exception is ECHO* where the option value may be modified. ECHO for a client means that it MUST echo the option it got in the last message from the server in the following messages it sends. RQ means that the server SHOULD include the option in the response, when requested by the client using the Option Request option. 6. Client Behaviour We will consider how a typical interactive client using the above protocol would behave. A client need only require a user to specify the unicast address of the server. It can then send an Init message with a prefix option containing the desired address family and zero prefix length. The server is then free to decide which group it should return. A client may also allow a user to specify a group address(es) or prefix(es) (for IPv6, the user may only be required to specify a scope or an RP address, from which the client can construct the desired prefix, possibly embedded-RP). From this the client can specify one or more prefix options in an Init message to tell the server which address it would prefer. If the user specifies a group address, that can be encoded as a prefix of maximal length (e.g. 32 for IPv4). The prefix options are in prioritised order, i.e., the client should put the most preferred prefix first. If the client receives a Server Response message containing a group address it can start sending Request messages, see the next paragraph. If there is no group address option, it would typically exit with an error message. The server may have included some prefix options in the Server Response. The client may use this to provide the user some feedback on what prefixes or scopes are available. Assuming the client got a group address in a Server Response it can start pinging. Before it does that it should let the user know which group is being used. When sending ping Requests the client must always specifiy the group option. If the last message from the server contained a Session ID, then it MUST also include that with the same value. Typically it would receive a Session ID in a Server Response together with the group address, and then the ID would stay the same during the entire ping sequence. However, if for instance the server process is restarted, it may still be possible to continue pinging but the Session ID MAY be changed by the server. Hence a client implementation MUST always use the last Session ID it received, and not necessarily the one from the Server Response message. If a client receives a Server Response message in response to a Request message (that is, a Server Response message containing a sequence number), this means there is an error and it should stop sending Requests. This may for instance happen after server restart. The client may have an option for the user to obtain server information. If the user asks for server information, the client can send an Init message with no prefix options, but with an Option Request Option, requesting the server to return a Server Information option. The server will return server information if supported, and it may also return a list of prefixes it supports. It will however not return a group address. The client may also try to obtain only a list of prefixes by sending an Init message with no prefixes and not requesting any specific options. Note that a client may pick a multicast group and send Request messages without first going through the Init - Server Response negotiation. If this is supported by the server and the server is okay with the group used, the server can then send Reply messages as usual. If the server is not okay, it will send a Server Response telling the client to stop and possibly pick a new group. 7. Server Behaviour We will consider how a typical server using the above protocol would behave. First we consider how to respond to Init messages. If the Init message contains prefix options, the server should look at them in order and see if it can assign a multicast address in the given range. The server would be configured, possibly have a default, specifying which groups it can offer. It may have a large pool just picking a group at random, possibly choose a group based on hashing of the clients IP address or identifier, or just use a fixed group. It is left to the server to decide whether it should allow the same address to be used simultaneously by multiple clients. If the server finds a suitable group address, it returns this in a group option in a Server Response message. The server may additionally include a Session ID. This may help the server if it is to keep some state, for instance for making sure the client uses the group it got assigned. A good Session ID would be a random byte string that is hard to predict. If the server cannot find a suitable group address, or if there were no prefixes in the Init message, it may send a Server Response message containing prefix options listing what prefixes may be available to the client. Finally, if the Init message requests the Server Information option, it should include that. When the server receives a Request message, it may first check that the group address and Session ID (if provided) are valid. If the server is satisfied it will send a unicast Reply message back to the client, and also a multicast Reply message to the group address. The Reply messages contain the exact options and in the same order, as in the Request (only exception is the pad option), and after that the server adds a TTL option and additional options if needed. E.g., it may add a timestamp if requested by the client. If the server is not happy with the group address and Session ID, it may send a Server Response message asking the client to stop. This Server Response must echo the sequence number from the Request. This Server Response may contain which prefixes the client can try to request addresses from. The unicast and multicast Reply messages have identical UDP payload apart from possibly TTL and timestamp option values. Note that the server may receive Request messages with no prior Init message. This may happen when the server restarts or if a response (answer).client sends a Request with no prior Init message. The options follow right after the type octetserver may go ahead and are not alignedrespond if it is okay with the group used. In the responses it may add a Session ID which will then be in any way (no spacing or padding). I.e., options might start at any octet boundary.later requests from the client. If the group is not okay, the server sends back a Server Response. The option formatResponse is specified above. 5.just as if it got an Init message with no prefixes. If the server adds or modifies the SessionID in replies, it MUST use the exact same SessionID in the unicast and multicast replies. 8. Acknowledgements The ssmping concept was proposed by Pavan Namburi, Kamil Sarac and Kevin C. Almeroth in the paper SSM-Ping: A Ping Utility for Source Specific Multicast, and also the Internet Draft draft-sarac-mping-00.txt. Mickael Hoerdt has contributed with several ideas. Alexander Gall, Nicholas Humfrey, Nick Lamb and Dave Thaler have contributed in different ways to mythe implementation of the ssmping tools at . Many people in communities like TERENA, Internet2 and the M6Bone have used early implementations of ssmping and provided feedback that have influenced the current protocol. Thanks to Kevin Almeroth, Toerless Eckert, Gorry Fairhurst, Liu Hui, Bharat Joshi, Olav Kvittem, Kamil Sarac, Pekka Savola, Trond Skjesol and Cao Wei for reviewing and providing feedback on this draft. 6.9. IANA Considerations As currently specified, ssmping would needIANA is requested to provide a well knownUDP port number which the servers listen to. It might be desirable tofor use SRV records instead or in addition to this. For IPv6 SSM ssmping should ideally have a reserved group ID. For the optional ASM functionality it would be useful to have a reserved IPv6 group ID,by this may be the same as the one used for SSM. It may also be useful to have a dedicated group for the optional IPv4 ASM functionality. This section needs further work. There mayprotocol, and also beprovide a needregistry for anssmping option registry. The exact IANA considerations need to be clarified before this document can go to working group last call. 7.types. 10. Security Considerations There are some security issues to consider. One is that a host may send a request with an IP source address of another host, and make a randoman arbitrary ssmping server on the Internet send packets to this other host. This hehaviour is fairly harmless. The worst case is if the host receiving the unicast replies also happen to be performing an ssmping test towards that particular server. In this unlikely eventevent, there would be an amplification effect where the host receives twice as many replies as there are requests sent. An ssmping server should perform rate limiting, to guard against this function being used as a DoS attack. A client should also use the client identifierID option to be able todistinguish replies to its own requests from replies that might be to other requests. How the protocol should be designed to cope with rate limiting at the server requires further study. One possibility might be that the server can choose to send generic replies, e.g. a packet every second without the usual client options but including sequence number and server time stamp, and where clients do not send requests as long as they receive generic replies. 8.11. References 126.96.36.199. Normative References  Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.  "IANA, Address Family Numbers", <http://www.iana.org/assignments/address-family-numbers>. 188.8.131.52. Informative References  "ssmping implementation", <http://www.venaas.no/multicast/ssmping/>. Authors' Addresses Stig Venaas UNINETT Trondheim NO-7465 Norway Email: firstname.lastname@example.org Hugo Santos Urb Glicinias, Smart Residence, 211 Aveiro 3810 PortugalNEC Europe Ltd. Kurfuersten-Anlage 36 Heidelberg 69115 Germany Email: email@example.com@nw.neclab.eu Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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