1dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\documentstyle[12pt,twoside]{article} 2dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\def\TITLE{IPv6 Flow Labels} 3dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\input preamble 4dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\begin{center} 5dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\Large\bf IPv6 Flow Labels in Linux-2.2. 6dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{center} 7dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 8dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 9dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\begin{center} 10dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat{ \large Alexey~N.~Kuznetsov } \\ 11dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\em Institute for Nuclear Research, Moscow \\ 12dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\verb|kuznet@ms2.inr.ac.ru| \\ 13dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\rm April 11, 1999 14dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{center} 15dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 16dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\vspace{5mm} 17dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 18dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\tableofcontents 19dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 20dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\section{Introduction.} 21dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 22dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatEvery IPv6 packet carries 28 bits of flow information. RFC2460 splits 23dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatthese bits to two fields: 8 bits of traffic class (or DS field, if you 24dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatprefer this term) and 20 bits of flow label. Currently there exist 25dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatno well-defined API to manage IPv6 flow information. In this document 26dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatI describe an attempt to design the API for Linux-2.2 IPv6 stack. 27dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 28dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\vskip 1mm 29dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 30dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatThe API must solve the following tasks: 31dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 32dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\begin{enumerate} 33dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 34dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item To allow user to set traffic class bits. 35dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 36dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item To allow user to read traffic class bits of received packets. 37dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatThis feature is not so useful as the first one, however it will be 38dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatnecessary f.e.\ to implement ECN [RFC2481] for datagram oriented services 39dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehator to implement receiver side of SRP or another end-to-end protocol 40dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatusing traffic class bits. 41dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 42dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item To assign flow labels to packets sent by user. 43dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 44dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item To get flow labels of received packets. I do not know 45dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatany applications of this feature, but it is possible that receiver will 46dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatwant to use flow labels to distinguish sub-flows. 47dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 48dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item To allocate flow labels in the way, compliant to RFC2460. Namely: 49dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 50dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\begin{itemize} 51dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item 52dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatFlow labels must be uniformly distributed (pseudo-)random numbers, 53dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatso that any subset of 20 bits can be used as hash key. 54dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 55dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item 56dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatFlows with coinciding source address and flow label must have identical 57dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatdestination address and not-fragmentable extensions headers (i.e.\ 58dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehathop by hop options and all the headers up to and including routing header, 59dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatif it is present.) 60dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 61dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\begin{NB} 62dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatThere is a hole in specs: some hop-by-hop options can be 63dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatdefined only on per-packet base (f.e.\ jumbo payload option). 64dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatEssentially, it means that such options cannot present in packets 65dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatwith flow labels. 66dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{NB} 67dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\begin{NB} 68dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatNB notes here and below reflect only my personal opinion, 69dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatthey should be read with smile or should not be read at all :-). 70dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{NB} 71dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 72dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 73dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item 74dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatFlow labels have finite lifetime and source is not allowed to reuse 75dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatflow label for another flow within the maximal lifetime has expired, 76dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatso that intermediate nodes will be able to invalidate flow state before 77dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatthe label is taken over by another flow. 78dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatFlow state, including lifetime, is propagated along datagram path 79dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatby some application specific methods 80dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat(f.e.\ in RSVP PATH messages or in some hop-by-hop option). 81dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 82dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 83dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{itemize} 84dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 85dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{enumerate} 86dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 87dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\section{Sending/receiving flow information.} 88dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 89dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\paragraph{Discussion.} 90dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\addcontentsline{toc}{subsection}{Discussion} 91dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatIt was proposed (Where? I do not remember any explicit statement) 92dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatto solve the first four tasks using 93dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\verb|sin6_flowinfo| field added to \verb|struct| \verb|sockaddr_in6| 94dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat(see RFC2553). 95dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 96dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\begin{NB} 97dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat This method is difficult to consider as reasonable, because it 98dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat puts additional overhead to all the services, despite of only 99dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat very small subset of them (none, to be more exact) really use it. 100dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat It contradicts both to IETF spirit and the letter. Before RFC2553 101dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat one justification existed, IPv6 address alignment left 4 byte 102dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat hole in \verb|sockaddr_in6| in any case. Now it has no justification. 103dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{NB} 104dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 105dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatWe have two problems with this method. The first one is common for all OSes: 106dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatif \verb|recvmsg()| initializes \verb|sin6_flowinfo| to flow info 107dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatof received packet, we loose one very important property of BSD socket API, 108dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatnamely, we are not allowed to use received address for reply directly 109dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatand have to mangle it, even if we are not interested in flowinfo subtleties. 110dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 111dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\begin{NB} 112dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat RFC2553 adds new requirement: to clear \verb|sin6_flowinfo|. 113dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat Certainly, it is not solution but rather attempt to force applications 114dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat to make unnecessary work. Well, as usually, one mistake in design 115dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat is followed by attempts to patch the hole and more mistakes... 116dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{NB} 117dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 118dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatAnother problem is Linux specific. Historically Linux IPv6 did not 119dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatinitialize \verb|sin6_flowinfo| at all, so that, if kernel does not 120dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatsupport flow labels, this field is not zero, but a random number. 121dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatSome applications also did not take care about it. 122dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 123dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\begin{NB} 124dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatFollowing RFC2553 such applications can be considered as broken, 125dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatbut I still think that they are right: clearing all the address 126dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatbefore filling known fields is robust but stupid solution. 127dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatUseless wasting CPU cycles and 128dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatmemory bandwidth is not a good idea. Such patches are acceptable 129dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatas temporary hacks, but not as standard of the future. 130dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{NB} 131dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 132dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 133dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\paragraph{Implementation.} 134dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\addcontentsline{toc}{subsection}{Implementation} 135dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatBy default Linux IPv6 does not read \verb|sin6_flowinfo| field 136dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatassuming that common applications are not obliged to initialize it 137dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatand are permitted to consider it as pure alignment padding. 138dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatIn order to tell kernel that application 139dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatis aware of this field, it is necessary to set socket option 140dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\verb|IPV6_FLOWINFO_SEND|. 141dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 142dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\begin{verbatim} 143dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat int on = 1; 144dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat setsockopt(sock, SOL_IPV6, IPV6_FLOWINFO_SEND, 145dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat (void*)&on, sizeof(on)); 146dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{verbatim} 147dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 148dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatLinux kernel never fills \verb|sin6_flowinfo| field, when passing 149dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatmessage to user space, though the kernels which support flow labels 150dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatinitialize it to zero. If user wants to get received flowinfo, he 151dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatwill set option \verb|IPV6_FLOWINFO| and after this he will receive 152dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatflowinfo as ancillary data object of type \verb|IPV6_FLOWINFO| 153dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat(cf.\ RFC2292). 154dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 155dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\begin{verbatim} 156dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat int on = 1; 157dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat setsockopt(sock, SOL_IPV6, IPV6_FLOWINFO, (void*)&on, sizeof(on)); 158dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{verbatim} 159dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 160dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatFlowinfo received and latched by a connected TCP socket also may be fetched 161dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatwith \verb|getsockopt()| \verb|IPV6_PKTOPTIONS| together with 162dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatanother optional information. 163dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 164dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatBesides that, in the spirit of RFC2292 the option \verb|IPV6_FLOWINFO| 165dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatmay be used as alternative way to send flowinfo with \verb|sendmsg()| or 166dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatto latch it with \verb|IPV6_PKTOPTIONS|. 167dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 168dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\paragraph{Note about IPv6 options and destination address.} 169dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\addcontentsline{toc}{subsection}{IPv6 options and destination address} 170dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatIf \verb|sin6_flowinfo| does contain not zero flow label, 171dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatdestination address in \verb|sin6_addr| and non-fragmentable 172dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatextension headers are ignored. Instead, kernel uses the values 173dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatcached at flow setup (see below). However, for connected sockets 174dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatkernel prefers the values set at connection time. 175dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 176dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\paragraph{Example.} 177dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\addcontentsline{toc}{subsection}{Example} 178dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatAfter setting socket option \verb|IPV6_FLOWINFO| 179dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatflowlabel and DS field are received as ancillary data object 180dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatof type \verb|IPV6_FLOWINFO| and level \verb|SOL_IPV6|. 181dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatIn the cases when it is convenient to use \verb|recvfrom(2)|, 182dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatit is possible to replace library variant with your own one, 183dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatsort of: 184dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 185dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\begin{verbatim} 186dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat#include <sys/socket.h> 187dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat#include <netinet/in6.h> 188dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 189dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatsize_t recvfrom(int fd, char *buf, size_t len, int flags, 190dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat struct sockaddr *addr, int *addrlen) 191dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat{ 192dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat size_t cc; 193dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat char cbuf[128]; 194dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat struct cmsghdr *c; 195dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat struct iovec iov = { buf, len }; 196dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat struct msghdr msg = { addr, *addrlen, 197dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat &iov, 1, 198dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat cbuf, sizeof(cbuf), 199dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 0 }; 200dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 201dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat cc = recvmsg(fd, &msg, flags); 202dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat if (cc < 0) 203dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat return cc; 204dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat ((struct sockaddr_in6*)addr)->sin6_flowinfo = 0; 205dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat *addrlen = msg.msg_namelen; 206dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat for (c=CMSG_FIRSTHDR(&msg); c; c = CMSG_NEXTHDR(&msg, c)) { 207dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat if (c->cmsg_level != SOL_IPV6 || 208dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat c->cmsg_type != IPV6_FLOWINFO) 209dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat continue; 210dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat ((struct sockaddr_in6*)addr)->sin6_flowinfo = *(__u32*)CMSG_DATA(c); 211dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat } 212dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat return cc; 213dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat} 214dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{verbatim} 215dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 216dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 217dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 218dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\section{Flow label management.} 219dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 220dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\paragraph{Discussion.} 221dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\addcontentsline{toc}{subsection}{Discussion} 222dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatRequirements of RFC2460 are pretty tough. Particularly, lifetimes 223dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatlonger than boot time require to store allocated labels at stable 224dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatstorage, so that the full implementation necessarily includes user space flow 225dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatlabel manager. There are at least three different approaches: 226dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 227dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\begin{enumerate} 228dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item {\bf ``Cooperative''. } We could leave flow label allocation wholly 229dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatto user space. When user needs label he requests manager directly. The approach 230dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatis valid, but as any ``cooperative'' approach it suffers of security problems. 231dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 232dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\begin{NB} 233dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatOne idea is to disallow not privileged user to allocate flow 234dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatlabels, but instead to pass the socket to manager via \verb|SCM_RIGHTS| 235dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatcontrol message, so that it will allocate label and assign it to socket 236dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatitself. Hmm... the idea is interesting. 237dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{NB} 238dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 239dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item {\bf ``Indirect''.} Kernel redirects requests to user level daemon 240dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatand does not install label until the daemon acknowledged the request. 241dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatThe approach is the most promising, it is especially pleasant to recognize 242dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatparallel with IPsec API [RFC2367,Craig]. Actually, it may share API with 243dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatIPsec. 244dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 245dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item {\bf ``Stupid''.} To allocate labels in kernel space. It is the simplest 246dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatmethod, but it suffers of two serious flaws: the first, 247dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatwe cannot lease labels with lifetimes longer than boot time, the second, 248dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatit is sensitive to DoS attacks. Kernel have to remember all the obsolete 249dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatlabels until their expiration and malicious user may fastly eat all the 250dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatflow label space. 251dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 252dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{enumerate} 253dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 254dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatCertainly, I choose the most ``stupid'' method. It is the cheapest one 255dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatfor implementor (i.e.\ me), and taking into account that flow labels 256dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatstill have no serious applications it is not useful to work on more 257dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatadvanced API, especially, taking into account that eventually we 258dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatwill get it for no fee together with IPsec. 259dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 260dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 261dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\paragraph{Implementation.} 262dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\addcontentsline{toc}{subsection}{Implementation} 263dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatSocket option \verb|IPV6_FLOWLABEL_MGR| allows to 264dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatrequest flow label manager to allocate new flow label, to reuse 265dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatalready allocated one or to delete old flow label. 266dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatIts argument is \verb|struct| \verb|in6_flowlabel_req|: 267dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 268dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\begin{verbatim} 269dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatstruct in6_flowlabel_req 270dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat{ 271dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat struct in6_addr flr_dst; 272dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat __u32 flr_label; 273dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat __u8 flr_action; 274dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat __u8 flr_share; 275dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat __u16 flr_flags; 276dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat __u16 flr_expires; 277dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat __u16 flr_linger; 278dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat __u32 __flr_reserved; 279dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat /* Options in format of IPV6_PKTOPTIONS */ 280dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat}; 281dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{verbatim} 282dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 283dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\begin{itemize} 284dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 285dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item \verb|dst| is IPv6 destination address associated with the label. 286dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 287dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item \verb|label| is flow label value in network byte order. If it is zero, 288dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatkernel will allocate new pseudo-random number. Otherwise, kernel will try 289dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatto lease flow label ordered by user. In this case, it is user task to provide 290dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatnecessary flow label randomness. 291dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 292dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item \verb|action| is requested operation. Currently, only three operations 293dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatare defined: 294dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 295dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\begin{verbatim} 296dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat#define IPV6_FL_A_GET 0 /* Get flow label */ 297dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat#define IPV6_FL_A_PUT 1 /* Release flow label */ 298dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat#define IPV6_FL_A_RENEW 2 /* Update expire time */ 299dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{verbatim} 300dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 301dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item \verb|flags| are optional modifiers. Currently 302dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatonly \verb|IPV6_FL_A_GET| has modifiers: 303dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 304dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\begin{verbatim} 305dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat#define IPV6_FL_F_CREATE 1 /* Allowed to create new label */ 306dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat#define IPV6_FL_F_EXCL 2 /* Do not create new label */ 307dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{verbatim} 308dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 309dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 310dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item \verb|share| defines who is allowed to reuse the same flow label. 311dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 312dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\begin{verbatim} 313dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat#define IPV6_FL_S_NONE 0 /* Not defined */ 314dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat#define IPV6_FL_S_EXCL 1 /* Label is private */ 315dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat#define IPV6_FL_S_PROCESS 2 /* May be reused by this process */ 316dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat#define IPV6_FL_S_USER 3 /* May be reused by this user */ 317dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat#define IPV6_FL_S_ANY 255 /* Anyone may reuse it */ 318dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{verbatim} 319dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 320dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item \verb|linger| is time in seconds. After the last user releases flow 321dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatlabel, it will not be reused with different destination and options at least 322dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatduring this time. If \verb|share| is not \verb|IPV6_FL_S_EXCL| the label 323dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatstill can be shared by another sockets. Current implementation does not allow 324dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatunprivileged user to set linger longer than 60 sec. 325dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 326dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item \verb|expires| is time in seconds. Flow label will be kept at least 327dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatfor this time, but it will not be destroyed before user released it explicitly 328dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehator closed all the sockets using it. Current implementation does not allow 329dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatunprivileged user to set timeout longer than 60 sec. Proviledged applications 330dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatMAY set longer lifetimes, but in this case they MUST save allocated 331dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatlabels at stable storage and restore them back after reboot before the first 332dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatapplication allocates new flow. 333dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 334dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{itemize} 335dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 336dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatThis structure is followed by optional extension headers associated 337dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatwith this flow label in format of \verb|IPV6_PKTOPTIONS|. Only 338dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\verb|IPV6_HOPOPTS|, \verb|IPV6_RTHDR| and, if \verb|IPV6_RTHDR| presents, 339dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\verb|IPV6_DSTOPTS| are allowed. 340dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 341dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\paragraph{Example.} 342dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\addcontentsline{toc}{subsection}{Example} 343dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat The function \verb|get_flow_label| allocates 344dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatprivate flow label. 345dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 346dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\begin{verbatim} 347dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatint get_flow_label(int fd, struct sockaddr_in6 *dst, __u32 fl) 348dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat{ 349dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat int on = 1; 350dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat struct in6_flowlabel_req freq; 351dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 352dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat memset(&freq, 0, sizeof(freq)); 353dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat freq.flr_label = htonl(fl); 354dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat freq.flr_action = IPV6_FL_A_GET; 355dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat freq.flr_flags = IPV6_FL_F_CREATE | IPV6_FL_F_EXCL; 356dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat freq.flr_share = IPV6_FL_S_EXCL; 357dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat memcpy(&freq.flr_dst, &dst->sin6_addr, 16); 358dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat if (setsockopt(fd, SOL_IPV6, IPV6_FLOWLABEL_MGR, 359dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat &freq, sizeof(freq)) == -1) { 360dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat perror ("can't lease flowlabel"); 361dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat return -1; 362dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat } 363dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat dst->sin6_flowinfo |= freq.flr_label; 364dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 365dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat if (setsockopt(fd, SOL_IPV6, IPV6_FLOWINFO_SEND, 366dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat &on, sizeof(on)) == -1) { 367dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat perror ("can't send flowinfo"); 368dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 369dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat freq.flr_action = IPV6_FL_A_PUT; 370dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat setsockopt(fd, SOL_IPV6, IPV6_FLOWLABEL_MGR, 371dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat &freq, sizeof(freq)); 372dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat return -1; 373dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat } 374dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat return 0; 375dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat} 376dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{verbatim} 377dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 378dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatA bit more complicated example using routing header can be found 379dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatin \verb|ping6| utility (\verb|iputils| package). Linux rsvpd backend 380dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatcontains an example of using operation \verb|IPV6_FL_A_RENEW|. 381dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 382dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\paragraph{Listing flow labels.} 383dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\addcontentsline{toc}{subsection}{Listing flow labels} 384dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatList of currently allocated 385dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatflow labels may be read from \verb|/proc/net/ip6_flowlabel|. 386dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 387dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\begin{verbatim} 388dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatLabel S Owner Users Linger Expires Dst Opt 389dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatA1BE5 1 0 0 6 3 3ffe2400000000010a0020fffe71fb30 0 390dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{verbatim} 391dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 392dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\begin{itemize} 393dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item \verb|Label| is hexadecimal flow label value. 394dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item \verb|S| is sharing style. 395dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item \verb|Owner| is ID of creator, it is zero, pid or uid, depending on 396dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat sharing style. 397dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item \verb|Users| is number of applications using the label now. 398dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item \verb|Linger| is \verb|linger| of this label in seconds. 399dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item \verb|Expires| is time until expiration of the label in seconds. It may 400dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat be negative, if the label is in use. 401dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item \verb|Dst| is IPv6 destination address. 402dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\item \verb|Opt| is length of options, associated with the label. Option 403dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat data are not accessible. 404dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{itemize} 405dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 406dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 407dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\paragraph{Flow labels and RSVP.} 408dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\addcontentsline{toc}{subsection}{Flow labels and RSVP} 409dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatRSVP daemon supports IPv6 flow labels 410dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatwithout any modifications to standard ISI RAPI. Sender must allocate 411dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatflow label, fill corresponding sender template and submit it to local rsvp 412dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatdaemon. rsvpd will check the label and start to announce it in PATH 413dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatmessages. Rsvpd on sender node will renew the flow label, so that it will not 414dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatbe reused before path state expires and all the intermediate 415dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatrouters and receiver purge flow state. 416dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 417dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\verb|rtap| utility is modified to parse flow labels. F.e.\ if user allocated 418dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehatflow label \verb|0xA1234|, he may write: 419dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 420dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\begin{verbatim} 421dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatRTAP> sender 3ffe:2400::1/FL0xA1234 <Tspec> 422dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{verbatim} 423dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 424dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatReceiver makes reservation with command: 425dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\begin{verbatim} 426dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San MehatRTAP> reserve ff 3ffe:2400::1/FL0xA1234 <Flowspec> 427dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{verbatim} 428dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat 429dcfb7a77f8709125e97c313cb8ab6ec4d87468f4San Mehat\end{document} 430