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author | Yoshinobu Inoue <shin@FreeBSD.org> | 2000-02-26 19:44:12 +0000 |
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committer | Yoshinobu Inoue <shin@FreeBSD.org> | 2000-02-26 19:44:12 +0000 |
commit | 80d21dc41ba277a75179ae197a69ae0255a9132c (patch) | |
tree | ba6036af6a1712f91ce2686f9a43088b7bddea5d /share/doc/IPv6 | |
parent | 99aa831bd47cd5d05523a22194e605a88e90e7a3 (diff) | |
download | src-80d21dc41ba277a75179ae197a69ae0255a9132c.tar.gz src-80d21dc41ba277a75179ae197a69ae0255a9132c.zip |
Add IPv6 related docs.
Reviewed by: phantom
Notes
Notes:
svn path=/head/; revision=57522
Diffstat (limited to 'share/doc/IPv6')
-rw-r--r-- | share/doc/IPv6/IMPLEMENTATION | 998 |
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diff --git a/share/doc/IPv6/IMPLEMENTATION b/share/doc/IPv6/IMPLEMENTATION new file mode 100644 index 000000000000..5909a7262480 --- /dev/null +++ b/share/doc/IPv6/IMPLEMENTATION @@ -0,0 +1,998 @@ + Implementation Note + + KAME Project + http://www.kame.net/ + $FreeBSD$ + +1. IPv6 + +1.1 Conformance + +The KAME kit conforms, or tries to conform, to the latest set of IPv6 +specifications. For future reference we list some of the relevant documents +below (NOTE: this is not a complete list - this is too hard to maintain...). +For details please refer to specific chapter in the document, RFCs, manpages +come with KAME, or comments in the source code. + +Conformance tests have been performed on the KAME STABLE kit +at TAHI project. Results can be viewed at http://www.tahi.org/report/KAME/. +We also attended Univ. of New Hampshire IOL tests (http://www.iol.unh.edu/) +in the past, with our past snapshots. + +RFC1639: FTP Operation Over Big Address Records (FOOBAR) + * RFC2428 is preferred over RFC1639. ftp clients will first try RFC2428, + then RFC1639 if failed. +RFC1886: DNS Extensions to support IPv6 +RFC1933: Transition Mechanisms for IPv6 Hosts and Routers + * IPv4 compatible address is not supported. + * automatic tunneling (4.3) is not supported. + * "gif" interface implements IPv[46]-over-IPv[46] tunnel in a generic way, + and it covers "configured tunnel" described in the spec. + See 1.5 in this document for details. +RFC1981: Path MTU Discovery for IPv6 +RFC2080: RIPng for IPv6 + * KAME-supplied route6d, bgpd and hroute6d support this. +RFC2283: Multiprotocol Extensions for BGP-4 + * so-called "BGP4+". + * KAME-supplied bgpd supports this. +RFC2292: Advanced Sockets API for IPv6 + * For supported library functions/kernel APIs, see sys/netinet6/ADVAPI. +RFC2362: Protocol Independent Multicast-Sparse Mode (PIM-SM) + * RFC2362 defines packet formats for PIM-SM. draft-ietf-pim-ipv6-01.txt + is written based on this. +RFC2373: IPv6 Addressing Architecture + * KAME supports node required addresses, and conforms to the scope + requirement. +RFC2374: An IPv6 Aggregatable Global Unicast Address Format + * KAME supports 64-bit length of Interface ID. +RFC2375: IPv6 Multicast Address Assignments + * Userland applications use the well-known addresses assigned in the RFC. +RFC2428: FTP Extensions for IPv6 and NATs + * RFC2428 is preferred over RFC1639. ftp clients will first try RFC2428, + then RFC1639 if failed. +RFC2460: IPv6 specification +RFC2461: Neighbor discovery for IPv6 + * See 1.2 in this document for details. +RFC2462: IPv6 Stateless Address Autoconfiguration + * See 1.4 in this document for details. +RFC2463: ICMPv6 for IPv6 specification + * See 1.8 in this document for details. +RFC2464: Transmission of IPv6 Packets over Ethernet Networks +RFC2465: MIB for IPv6: Textual Conventions and General Group + * Necessary statistics are gathered by the kernel. Actual IPv6 MIB + support is provided as patchkit for ucd-snmp. +RFC2466: MIB for IPv6: ICMPv6 group + * Necessary statistics are gathered by the kernel. Actual IPv6 MIB + support is provided as patchkit for ucd-snmp. +RFC2467: Transmission of IPv6 Packets over FDDI Networks +RFC2472: IPv6 over PPP +RFC2492: IPv6 over ATM Networks + * only PVC is supported. +RFC2497: Transmission of IPv6 packet over ARCnet Networks +RFC2545: Use of BGP-4 Multiprotocol Extensions for IPv6 Inter-Domain Routing +RFC2553: Basic Socket Interface Extensions for IPv6 + * IPv4 mapped address (3.7) and special behavior of IPv6 wildcard bind + socket (3.8) are supported. + see 1.12 in this document for details. +RFC2675: IPv6 Jumbograms + * See 1.7 in this document for details. +RFC2710: Multicast Listener Discovery for IPv6 +RFC2711: IPv6 router alert option +draft-ietf-ipngwg-router-renum-08: Router renumbering for IPv6 +draft-ietf-ipngwg-icmp-namelookups-02: IPv6 Name Lookups Through ICMP +draft-ietf-ipngwg-icmp-name-lookups-03: IPv6 Name Lookups Through ICMP +draft-ietf-pim-ipv6-01.txt: PIM for IPv6 + * pim6dd implements dense mode. pim6sd implements sparse mode. +draft-ietf-dhc-dhcpv6-14.txt: DHCPv6 +draft-ietf-dhc-v6exts-11.txt: Extensions for DHCPv6 + * kame/dhcp6 has test implementation, which will not be compiled in + default compilation. +draft-itojun-ipv6-tcp-to-anycast-00: + Disconnecting TCP connection toward IPv6 anycast address +draft-yamamoto-wideipv6-comm-model-00 + * See 1.6 in this document for details. +draft-ietf-ipngwg-scopedaddr-format-00.txt: + An Extension of Format for IPv6 Scoped Addresses + +1.2 Neighbor Discovery + +Neighbor Discovery is fairly stable. Currently Address Resolution, +Duplicated Address Detection, and Neighbor Unreachability Detection +are supported. In the near future we will be adding Proxy Neighbor +Advertisement support in the kernel and Unsolicited Neighbor Advertisement +transmission command as admin tool. + +If DAD fails, the address will be marked "duplicated" and message will be +generated to syslog (and usually to console). The "duplicated" mark +can be checked with ifconfig. It is administrators' responsibility to check +for and recover from DAD failures. +The behavior should be improved in the near future. + +Some of the network driver loops multicast packets back to itself, +even if instructed not to do so (especially in promiscuous mode). +In such cases DAD may fail, because DAD engine sees inbound NS packet +(actually from the node itself) and considers it as a sign of duplicate. +You may want to look at #if condition marked "heuristics" in +sys/netinet6/nd6_nbr.c:nd6_dad_timer() as workaround (note that the code +fragment in "heuristics" section is not spec conformant). + +Neighbor Discovery specification (RFC2461) does not talk about neighbor +cache handling in the following cases: +(1) when there was no neighbor cache entry, node received unsolicited + RS/NS/NA/redirect packet without link-layer address +(2) neighbor cache handling on medium without link-layer address + (we need a neighbor cache entry for IsRouter bit) +For (1), we implemented workaround based on discussions on IETF ipngwg mailing +list. For more details, see the comments in the source code and email +thread started from (IPng 7155), dated Feb 6 1999. + +IPv6 on-link determination rule (RFC2461) is quite different from assumptions +in BSD network code. At this moment, KAME does not implement on-link +determination rule when default router list is empty (RFC2461, section 5.2, +last sentence in 2nd paragraph - note that the spec misuse the word "host" +and "node" in several places in the section). + +To avoid possible DoS attacks and infinite loops, KAME stack will accept +only 10 options on ND packet. Therefore, if you have 20 prefix options +attached to RA, only the first 10 prefixes will be recognized. +If this troubles you, please contact KAME team and/or modify +nd6_maxndopt in sys/netinet6/nd6.c. If there are high demands we may +provide sysctl knob for the variable. + +1.3 Scope Index + +IPv6 uses scoped addresses. Therefore, it is very important to +specify scope index (interface index for link-local address, or +site index for site-local address) with an IPv6 address. Without +scope index, scoped IPv6 address is ambiguous to the kernel, and +kernel will not be able to determine the outbound interface for a +packet. + +Ordinary userland applications should use advanced API (RFC2292) to +specify scope index, or interface index. For similar purpose, +sin6_scope_id member in sockaddr_in6 structure is defined in RFC2553. +However, the semantics for sin6_scope_id is rather vague. If you +care about portability of your application, we suggest you to use +advanced API rather than sin6_scope_id. + +In the kernel, an interface index for link-local scoped address is +embedded into 2nd 16bit-word (3rd and 4th byte) in IPv6 address. +For example, you may see something like: + fe80:1::200:f8ff:fe01:6317 +in the routing table and interface address structure (struct +in6_ifaddr). The address above is a link-local unicast address +which belongs to a network interface whose interface identifier is 1. +The embedded index enables us to identify IPv6 link local +addresses over multiple interfaces effectively and with only a +little code change. +Routing daemons and configuration programs, like route6d and +ifconfig, will need to manipulate the "embedded" scope index. +These programs use routing sockets and ioctls (like SIOCGIFADDR_IN6) +and the kernel API will return IPv6 addresses with 2nd 16bit-word +filled in. The APIs are for manipulating kernel internal structure. +Programs that use these APIs have to be prepared about differences +in kernels anyway. + +When you specify scoped address to the command line, NEVER write the +embedded form (such as ff02:1::1 or fe80:2::fedc). This is not supposed +to work. Always use standard form, like ff02::1 or fe80::fedc, with +command line option for specifying interface (like "ping6 -I ne0 ff02::1). +In general, if a command does not have command line option to specify +outgoing interface, that command is not ready to accept scoped address. +This may seem to be opposite from IPv6's premise to support "dentist office" +situation. We believe that specifications need some improvements for this. + +Some of the userland tools support extended numeric IPv6 syntax, as +documented in draft-ietf-ipngwg-scopedaddr-format-00.txt. You can specify +outgoing link, by using name of the outgoing interface like "fe80::1%ne0". +This way you will be able to specify link-local scoped address without much +trouble. +To use this extension in your program, you'll need to use getaddrinfo(3), +and getnameinfo(3) with NI_WITHSCOPEID. +The implementation currently assumes 1-to-1 relationship between a link and an +interface, which is stronger than what specs say. + +1.4 Plug and Play + +The KAME kit implements most of the IPv6 stateless address +autoconfiguration in the kernel. +Neighbor Discovery functions are implemented in the kernel as a whole. +Router Advertisement (RA) input for hosts is implemented in the +kernel. Router Solicitation (RS) output for endhosts, RS input +for routers, and RA output for routers are implemented in the +userland. + +1.4.1 Assignment of link-local, and special addresses + +IPv6 link-local address is generated from IEEE802 adddress (ethernet MAC +address). Each of interface is assigned an IPv6 link-local address +automatically, when the interface becomes up (IFF_UP). Also, direct route +for the link-local address is added to routing table. + +Here is an output of netstat command: + +Internet6: +Destination Gateway Flags Netif Expire +fe80:1::%ed0/64 link#1 UC ed0 +fe80:2::%ep0/64 link#2 UC ep0 + +Interfaces that has no IEEE802 address (pseudo interfaces like tunnel +interfaces, or ppp interfaces) will borrow IEEE802 address from other +interfaces, such as ethernet interfaces, whenever possible. +If there is no IEEE802 hardware attached, last-resort pseudorandom value, +which is from MD5(hostname), will be used as source of link-local address. +If it is not suitable for your usage, you will need to configure the +link-local address manually. + +If an interface is not capable of handling IPv6 (such as lack of multicast +support), link-local address will not be assigned to that interface. +See section 2 for details. + +Each interface joins the solicited multicast address and the +link-local all-nodes multicast addresses (e.g. fe80::1:ff01:6317 +and ff02::1, respectively, on the link the interface is attached). +In addition to a link-local address, the loopback address (::1) will be +assigned to the loopback interface. Also, ::1/128 and ff01::/32 are +automatically added to routing table, and loopback interface joins +node-local multicast group ff01::1. + +1.4.2 Stateless address autoconfiguration on hosts + +In IPv6 specification, nodes are separated into two categories: +routers and hosts. Routers forward packets addressed to others, hosts does +not forward the packets. net.inet6.ip6.forwarding defines whether this +node is router or host (router if it is 1, host if it is 0). + +When a host hears Router Advertisement from the router, a host may +autoconfigure itself by stateless address autoconfiguration. +This behavior can be controlled by net.inet6.ip6.accept_rtadv +(host autoconfigures itself if it is set to 1). +By autoconfiguration, network address prefix for the receiving interface +(usually global address prefix) is added. Default route is also configured. +Routers periodically generate Router Advertisement packets. To request +an adjacent router to generate RA packet, a host can transmit Router +Solicitation. To generate a RS packet at any time, use the "rtsol" command. +"rtsold" daemon is also available. "rtsold" generates Router Solicitation +whenever necessary, and it works great for nomadic usage (notebooks/laptops). +If one wishes to ignore Router Advertisements, use sysctl to set +net.inet6.ip6.accept_rtadv to 0. + +To generate Router Advertisement from a router, use the "rtadvd" daemon. + +Note that, IPv6 specification assumes the following items, and nonconforming +cases are left unspecified: +- Only hosts will listen to router advertisements +- Hosts have single network interface (except loopback) +Therefore, this is unwise to enable net.inet6.ip6.accept_rtadv on routers, +or multi-interface host. A misconfigured node can behave strange +(KAME code allows nonconforming configuration, for those who would like +to do some experiments). + +To summarize the sysctl knob: + accept_rtadv forwarding role of the node + --- --- --- + 0 0 host (to be manually configured) + 0 1 router + 1 0 autoconfigured host + (spec assumes that host has single + interface only, autoconfigured host + with multiple interface is + out-of-scope) + 1 1 invalid, or experimental + (out-of-scope of spec) + +RFC2462 has validation rule against incoming RA prefix information option, +in 5.5.3 (e). This is to protect hosts from malicious (or misconfigured) +routers that advertise very short prefix lifetime. +There was an update from Jim Bound to ipngwg mailing list (look +for "(ipng 6712)" in the archive) and KAME implements Jim's update. + +See 1.2 in the document for relationship between DAD and autoconfiguration. + +1.4.3 DHCPv6 (not yet put into freebsd4.0) + +We supply a tiny DHCPv6 server/client in kame/dhcp6. However, the +implementation is very premature (for example, this does NOT +implement address lease/release), and it is not in default compilation +tree. If you want to do some experiment, compile it on your own. + +DHCPv6 and autoconfiguration also needs more work. "Managed" and "Other" +bits in RA have no special effect to stateful autoconfiguration procedure +in DHCPv6 client program ("Managed" bit actually prevents stateless +autoconfiguration, but no special action will be taken for DHCPv6 client). + +1.5 Generic tunnel interface + +GIF (Generic InterFace) is a pseudo interface for configured tunnel. +Details are described in gif(4) manpage. +Currently + v6 in v6 + v6 in v4 + v4 in v6 + v4 in v4 +are available. Use "gifconfig" to assign physical (outer) source +and destination address to gif interfaces. +Configuration that uses same address family for inner and outer IP +header (v4 in v4, or v6 in v6) is dangerous. It is very easy to +configure interfaces and routing tables to perform infinite level +of tunneling. Please be warned. + +gif can be configured to be ECN-friendly. See 4.5 for ECN-friendliness +of tunnels, and gif(4) manpage for how to configure. + +If you would like to configure an IPv4-in-IPv6 tunnel with gif interface, +read gif(4) carefully. You will need to remove IPv6 link-local address +automatically assigned to the gif interface. + +1.6 Source Address Selection + +Source selection of KAME is scope oriented (there are some exceptions - +see below). For a given destination, a source IPv6 address is selected +by the following rule: + 1. If the source address is explicitly specified by the user + (e.g. via the advanced API), the specified address is used. + 2. If there is an address assigned to the outgoing interface + (which is usually determined by looking up the routing table) + that has the same scope as the destination address, the address + is used. + This is the most typical case. + 3. If there is no address that satisfies the above condition, + choose a global address assigned to one of the interfaces + on the sending node. + 4. If there is no address that satisfies the above condition, + and destination address is site local scope, + choose a site local address assigned to one of the interfaces + on the sending node. + 5. If there is no address that satisfies the above condition, + choose the address associated with the routing table + entry for the destination. + This is the last resort, which may cause scope violation. + +For instance, ::1 is selected for ff01::1, fe80:1::200:f8ff:fe01:6317 +for fe80:1::2a0:24ff:feab:839b (note that embedded interface index - +described in 1.3 - helps us choose the right source address. Those +embedded indices will not be on the wire). +If the outgoing interface has multiple address for the scope, +a source is selected longest match basis (rule 3). Suppose +3ffe:501:808:1:200:f8ff:fe01:6317 and 3ffe:2001:9:124:200:f8ff:fe01:6317 +are given to the outgoing interface. 3ffe:501:808:1:200:f8ff:fe01:6317 +is chosen as the source for the destination 3ffe:501:800::1. + +Note that the above rule is not documented in the IPv6 spec. It is +considered "up to implementation" item. +There are some cases where we do not use the above rule. One +example is connected TCP session, and we use the address kept in tcb +as the source. +Another example is source address for Neighbor Advertisement. +Under the spec (RFC2461 7.2.2) NA's source should be the target +address of the corresponding NS's target. In this case we follow +the spec rather than the above longest-match rule. + +For new connections (when rule 1 does not apply), deprecated addresses +(addresses with preferred lifetime = 0) will not be chosen as source address +if other choises are available. If no other choices are available, +deprecated address will be used as a last resort. If there are multiple +choice of deprecated addresses, the above scope rule will be used to choose +from those deprecated addreses. If you would like to prohibit the use +of deprecated address for some reason, configure net.inet6.ip6.use_deprecated +to 0. The issue related to deprecated address is described in RFC2462 5.5.4 +(NOTE: there is some debate underway in IETF ipngwg on how to use +"deprecated" address). + +1.7 Jumbo Payload + +KAME supports the Jumbo Payload hop-by-hop option used to send IPv6 +packets with payloads longer than 65,535 octets. But since currently +KAME does not support any physical interface whose MTU is more than +65,535, such payloads can be seen only on the loopback interface(i.e. +lo0). + +If you want to try jumbo payloads, you first have to reconfigure the +kernel so that the MTU of the loopback interface is more than 65,535 +bytes; add the following to the kernel configuration file: + options "LARGE_LOMTU" #To test jumbo payload +and recompile the new kernel. + +Then you can test jumbo payloads by the ping6 command with -b and -s +options. The -b option must be specified to enlarge the size of the +socket buffer and the -s option specifies the length of the packet, +which should be more than 65,535. For example, type as follows; + % ping6 -b 70000 -s 68000 ::1 + +The IPv6 specification requires that the Jumbo Payload option must not +be used in a packet that carries a fragment header. If this condition +is broken, an ICMPv6 Parameter Problem message must be sent to the +sender. KAME kernel follows the specification, but you cannot usually +see an ICMPv6 error caused by this requirement. + +If KAME kernel receives an IPv6 packet, it checks the frame length of +the packet and compares it to the length specified in the payload +length field of the IPv6 header or in the value of the Jumbo Payload +option, if any. If the former is shorter than the latter, KAME kernel +discards the packet and increments the statistics. You can see the +statistics as output of netstat command with `-s -p ip6' option: + % netstat -s -p ip6 + ip6: + (snip) + 1 with data size < data length + +So, KAME kernel does not send an ICMPv6 error unless the erroneous +packet is an actual Jumbo Payload, that is, its packet size is more +than 65,535 bytes. As described above, KAME kernel currently does not +support physical interface with such a huge MTU, so it rarely returns an +ICMPv6 error. + +TCP/UDP over jumbogram is not supported at this moment. This is because +we have no medium (other than loopback) to test this. Contact us if you +need this. + +IPsec does not work on jumbograms. This is due to some specification twists +in supporting AH with jumbograms (AH header size influences payload length, +and this makes it real hard to authenticate inbound packet with jumbo payload +option as well as AH). + +There are fundamental issues in *BSD support for jumbograms. We would like to +address those, but we need more time to finalize these. To name a few: +- mbuf pkthdr.len field is typed as "int" in 4.4BSD, so it will not hold + jumbogram with len > 2G on 32bit architecture CPUs. If we would like to + support jumbogram properly, the field must be expanded to hold 4G + + IPv6 header + link-layer header. Therefore, it must be expanded to at least + int64_t (u_int32_t is NOT enough). +- We mistakingly use "int" to hold packet length in many places. We need + to convert them into larger integral type. It needs a great care, as we may + experience overflow during packet length computation. +- We mistakingly check for ip6_plen field of IPv6 header for packet payload + length in various places. We should be checking mbuf pkthdr.len instead. + ip6_input() will perform sanity check on jumbo payload option on input, + and we can safely use mbuf pkthdr.len afterwards. +- TCP code needs a careful update in bunch of places, of course. + +1.8 Loop prevention in header processing + +IPv6 specification allows arbitrary number of extension headers to +be placed onto packets. If we implement IPv6 packet processing +code in the way BSD IPv4 code is implemented, kernel stack may +overflow due to long function call chain. KAME sys/netinet6 code +is carefully designed to avoid kernel stack overflow. Because of +this, KAME sys/netinet6 code defines its own protocol switch +structure, as "struct ip6protosw" (see netinet6/ip6protosw.h). +There is no such update to IPv4 part (sys/netinet) for +compatibility, but small change is added to its pr_input() +prototype. So "struct ipprotosw" is also defined. +Because of this, if you receive IPsec-over-IPv4 packet with massive +number of IPsec headers, kernel stack may blow up. IPsec-over-IPv6 is okay. +(Off-course, for those all IPsec headers to be processed, each +such IPsec header must pass each IPsec check. So an anonymous +attacker won't be able to do such an attack.) + +1.9 ICMPv6 + +After RFC2463 was published, IETF ipngwg has decided to disallow ICMPv6 error +packet against ICMPv6 redirect, to prevent ICMPv6 storm on a network medium. +KAME already implements this into the kernel. + +1.10 Applications + +For userland programming, we support IPv6 socket API as specified in +RFC2553, RFC2292 and upcoming internet drafts. + +TCP/UDP over IPv6 is available and quite stable. You can enjoy "telnet", +"ftp", "rlogin", "rsh", "ssh", etc. These applications are protocol +independent. That is, they automatically chooses IPv4 or IPv6 +according to DNS. + +1.11 Kernel Internals + + (*) TCP/UDP part is handled differently between operating system platforms. + See 1.12 for details. + +The current KAME has escaped from the IPv4 netinet logic. While +ip_forward() calls ip_output(), ip6_forward() directly calls +if_output() since routers must not divide IPv6 packets into fragments. + +ICMPv6 should contain the original packet as long as possible up to +1280. UDP6/IP6 port unreach, for instance, should contain all +extension headers and the *unchanged* UDP6 and IP6 headers. +So, all IP6 functions except TCP never convert network byte +order into host byte order, to save the original packet. + +tcp_input(), udp6_input() and icmp6_input() can't assume that IP6 +header is preceding the transport headers due to extension +headers. So, in6_cksum() was implemented to handle packets whose IP6 +header and transport header is not continuous. TCP/IP6 nor UDP6/IP6 +header structure don't exist for checksum calculation. + +To process IP6 header, extension headers and transport headers easily, +KAME requires network drivers to store packets in one internal mbuf or +one or more external mbufs. A typical old driver prepares two +internal mbufs for 96 - 204 bytes data, however, KAME's reference +implementation stores it in one external mbuf. + +"netstat -s -p ip6" tells you whether or not your driver conforms +KAME's requirement. In the following example, "cce0" violates the +requirement. (For more information, refer to Section 2.) + + Mbuf statistics: + 317 one mbuf + two or more mbuf:: + lo0 = 8 + cce0 = 10 + 3282 one ext mbuf + 0 two or more ext mbuf + +Each input function calls IP6_EXTHDR_CHECK in the beginning to check +if the region between IP6 and its header is +continuous. IP6_EXTHDR_CHECK calls m_pullup() only if the mbuf has +M_LOOP flag, that is, the packet comes from the loopback +interface. m_pullup() is never called for packets coming from physical +network interfaces. + +Both IP and IP6 reassemble functions never call m_pullup(). + +1.12 IPv4 mapped address and IPv6 wildcard socket + +RFC2553 describes IPv4 mapped address (3.7) and special behavior +of IPv6 wildcard bind socket (3.8). The spec allows you to: +- Accept IPv4 connections by AF_INET6 wildcard bind socket. +- Transmit IPv4 packet over AF_INET6 socket by using special form of + the address like ::ffff:10.1.1.1. +but the spec itself is very complicated and does not specify how the +socket layer should behave. +Here we call the former one "listening side" and the latter one "initiating +side", for reference purposes. + +Almost all KAME implementations treat tcp/udp port number space separately +between IPv4 and IPv6. You can perform wildcard bind on both of the adderss +families, on the same port. + +The following table show the behavior of FreeBSD4x. + + listening side initiating side + (AF_INET6 wildcard (connetion to ::ffff:10.1.1.1) + socket gets IPv4 conn.) + --- --- +FreeBSD4x configurable supported + default: enabled + +The following sections will give you more details, and how you can +configure the behavior. + +Comments on listening side: + +It looks that RFC2553 talks too little on wildcard bind issue, +especially on the port space issue, failure mode and relationship +between AF_INET/INET6 wildcard bind. There can be several separate +interpretation for this RFC which conform to it but behaves differently. +So, to implement portable application you should assume nothing +about the behavior in the kernel. Using getaddrinfo() is the safest way. +Port number space and wildcard bind issues were discussed in detail +on ipv6imp mailing list, in mid March 1999 and it looks that there's +no concrete consensus (means, up to implementers). You may want to +check the mailing list archives. + +If a server application would like to accept IPv4 and IPv6 connections, +there will be two alternatives. + +One is using AF_INET and AF_INET6 socket (you'll need two sockets). +Use getaddrinfo() with AI_PASSIVE into ai_flags, and socket(2) and bind(2) +to all the addresses returned. +By opening multiple sockets, you can accept connections onto the socket with +proper address family. IPv4 connections will be accepted by AF_INET socket, +and IPv6 connections will be accepted by AF_INET6 socket. + +Another way is using one AF_INET6 wildcard bind socket. +Use getaddrinfo() with AI_PASSIVE into ai_flags and with +AF_INET6 into ai_family, and set the 1st argument hostname to +NULL. And socket(2) and bind(2) to the address returned. +(should be IPv6 unspecified addr) +You can accept either of IPv4 and IPv6 packet via this one socket. + +To support only IPv6 traffic on AF_INET6 wildcard binded socket portably, +always check the peer address when a connection is made toward +AF_INET6 listening socket. If the address is IPv4 mapped address, you may +want to reject the connection. You can check the condition by using +IN6_IS_ADDR_V4MAPPED() macro. +To resolv this issue more easily, there is system dependent setsockopt() +option, IPV6_BINDV6ONLY, used like below. + int on; + + setsockopt(s, IPPROTO_IPV6, IPV6_BINDV6ONLY, + (char *)&on, sizeof (on)) < 0)); +When this call succeed, then this socket only receive IPv6 packets. + + +Comments on initiating side: + +Advise to application implementers: to implement a portable IPv6 application +(which works on multiple IPv6 kernels), we believe that the following +is the key to the success: +- NEVER hardcode AF_INET nor AF_INET6. +- Use getaddrinfo() and getnameinfo() throughout the system. + Never use gethostby*(), getaddrby*(), inet_*() or getipnodeby*(). + (To update existing applications to be IPv6 aware easily, + sometime getipnodeby*() will be useful. But if possible, try to + rewrite the code to use getaddrinfo() and getnameinfo().) +- If you would like to connect to destination, use getaddrinfo() and try + all the destination returned, like telnet does. +- Some of the IPv6 stack is shipped with buggy getaddrinfo(). Ship a minimal + working version with your application and use that as last resort. + +If you would like to use AF_INET6 socket for both IPv4 and IPv6 outgoing +connection, you will need to use getipnodebyname(). When you would like to +update your existing appication to be IPv6 aware with minimal effort, +this approach might be choosed. But please note that it is a temporal +solution, because getipnodebyname() itself is not recommended as it does +not handle scoped IPv6 addresses at all. For IPv6 name resolution, +getaddrinfo() is the preferred API. So you should rewrite your +application to use getaddrinfo(), when you get the time to do it. + +When writing applications that make outgoing connections, story goes much +simpler if you treat AF_INET and AF_INET6 as totally seaprate address family. +{set,get}sockopt issue goes simpler, DNS issue will be made simpler. We do +not recommend you to rely upon IPv4 mapped address. + +1.12.1 FreeBSD4x + +FreeBSD4x uses shared tcp4/6 code (from sys/netinet/tcp*) and separete +udp4/6 code. It uses unified inpcb/in6pcb structure. + +The platform can be configured to support IPv4 mapped address. +Kernel configuration is summarized as follows: +- By default, AF_INET6 socket will grab IPv4 connections in certain condition, + and can initiate connection to IPv4 destination embedded in + IPv4 mapped IPv6 address. +- You can disable it on entire system with sysctl like below. + sysctl -w net.inet6.ip6.mapped_addr=0 + +1.12.1.1 FreeBSD4x, listening side + +Each socket can be configured to support special AF_INET6 wildcard bind +(enabled by default). +You can disable it on each socket basis with setsockopt() like below. + int on; + + setsockopt(s, IPPROTO_IPV6, IPV6_BINDV6ONLY, + (char *)&on, sizeof (on)) < 0)); + +Wildcard AF_INET6 socket grabs IPv4 connection if and only if the following +conditions are satisfied: +- there's no AF_INET socket that matches the IPv4 connection +- the AF_INET6 socket is configured to accept IPv4 traffic, i.e. + getsockopt(IPV6_BINDV6ONLY) returns 0. +There's no problem with open/close ordering. + +1.12.1.2 FreeBSD4x, initiating side + +FreeBSD4x supports outgoing connetion to IPv4 mapped address +(::ffff:10.1.1.1), if the node is configured to support IPv4 mapped address. + +1.13 sockaddr_storage + +When RFC2553 was about to be finalized, there was discusson on how struct +sockaddr_storage members are named. One proposal is to prepend "__" to the +members (like "__ss_len") as they should not be touched. The other proposal +was that don't prepend it (like "ss_len") as we need to touch those members +directly. There was no clear consensus on it. + +As a result, RFC2553 defines struct sockaddr_storage as follows: + struct sockaddr_storage { + u_char __ss_len; /* address length */ + u_char __ss_family; /* address family */ + /* and bunch of padding */ + }; +On the contrary, XNET draft defines as follows: + struct sockaddr_storage { + u_char ss_len; /* address length */ + u_char ss_family; /* address family */ + /* and bunch of padding */ + }; + +In December 1999, it was agreed that RFC2553bis should pick the latter (XNET) +definition. + +KAME kit prior to December 1999 used RFC2553 definition. KAME kit after +December 1999 (including December) will conform to XNET definition, +based on RFC2553bis discusson. + +If you look at multiple IPv6 implementations, you will be able to see +both definitions. As an userland programmer, the most portable way of +dealing with it is to: +(1) ensure ss_family and/or ss_len are available on the platform, by using + GNU autoconf, +(2) have -Dss_family=__ss_family to unify all occurences (including header + file) into __ss_family, or +(3) never touch __ss_family. cast to sockaddr * and use sa_family like: + struct sockaddr_storage ss; + family = ((struct sockaddr *)&ss)->sa_family + +2. Network Drivers + +KAME requires two items to be added into the standard drivers: + +(1) mbuf clustering requirement. In this stable release, we changed + MINCLSIZE into MHLEN+1 for all the operating systems in order to make + all the drivers behave as we expect. + +(2) multicast. If "ifmcstat" yields no multicast group for a + interface, that interface has to be patched. + +If any of the driver don't support the requirements, then the driver +can't be used for IPv6 and/or IPsec communication. If you find any +problem with your card using IPv6/IPsec, then, please report it to +freebsd-bugs@freebsd.org. + +(NOTE: In the past we required all pcmcia drivers to have a call to +in6_ifattach(). We have no such requirement any more) + +3. Translator + +We categorize IPv4/IPv6 translator into 4 types. + +Translator A --- It is used in the early stage of transition to make +it possible to establish a connection from an IPv6 host in an IPv6 +island to an IPv4 host in the IPv4 ocean. + +Translator B --- It is used in the early stage of transition to make +it possible to establish a connection from an IPv4 host in the IPv4 +ocean to an IPv6 host in an IPv6 island. + +Translator C --- It is used in the late stage of transition to make it +possible to establish a connection from an IPv4 host in an IPv4 island +to an IPv6 host in the IPv6 ocean. + +Translator D --- It is used in the late stage of transition to make it +possible to establish a connection from an IPv6 host in the IPv6 ocean +to an IPv4 host in an IPv4 island. + +KAME provides an TCP relay translator for category A. This is called +"FAITH". We also provide IP header translator for category A. +(The latter is not yet put into FreeBSD4.x yet.) + +3.1 FAITH TCP relay translator + +FAITH system uses TCP relay daemon called "faithd" helped by the KAME kernel. +FAITH will reserve an IPv6 address prefix, and relay TCP connection +toward that prefix to IPv4 destination. + +For example, if the reserved IPv6 prefix is 3ffe:0501:0200:ffff::, and +the IPv6 destination for TCP connection is 3ffe:0501:0200:ffff::163.221.202.12, +the connection will be relayed toward IPv4 destination 163.221.202.12. + + destination IPv4 node (163.221.202.12) + ^ + | IPv4 tcp toward 163.221.202.12 + FAITH-relay dual stack node + ^ + | IPv6 TCP toward 3ffe:0501:0200:ffff::163.221.202.12 + source IPv6 node + +faithd must be invoked on FAITH-relay dual stack node. + +For more details, consult src/usr.sbin/faithd/README. + +3.2 IPv6-to-IPv4 header translator + +(to be written) + +4. IPsec + +IPsec is mainly organized by three components. + +(1) Policy Management +(2) Key Management +(3) AH and ESP handling + +4.1 Policy Management + +The kernel implements experimental policy management code. There are two way +to manage security policy. One is to configure per-socket policy using +setsockopt(3). In this cases, policy configuration is described in +ipsec_set_policy(3). The other is to configure kernel packet filter-based +policy using PF_KEY interface, via setkey(8). + +The policy entry is not re-ordered with its +indexes, so the order of entry when you add is very significant. + +4.2 Key Management + +The key management code implemented in this kit (sys/netkey) is a +home-brew PFKEY v2 implementation. This conforms to RFC2367. + +The home-brew IKE daemon, "racoon" is included in the kit +(kame/kame/racoon). +Basically you'll need to run racoon as daemon, then setup a policy +to require keys (like ping -P 'out ipsec esp/transport//use'). +The kernel will contact racoon daemon as necessary to exchange keys. + +4.3 AH and ESP handling + +IPsec module is implemented as "hooks" to the standard IPv4/IPv6 +processing. When sending a packet, ip{,6}_output() checks if ESP/AH +processing is required by checking if a matching SPD (Security +Policy Database) is found. If ESP/AH is needed, +{esp,ah}{4,6}_output() will be called and mbuf will be updated +accordingly. When a packet is received, {esp,ah}4_input() will be +called based on protocol number, i.e. (*inetsw[proto])(). +{esp,ah}4_input() will decrypt/check authenticity of the packet, +and strips off daisy-chained header and padding for ESP/AH. It is +safe to strip off the ESP/AH header on packet reception, since we +will never use the received packet in "as is" form. + +By using ESP/AH, TCP4/6 effective data segment size will be affected by +extra daisy-chained headers inserted by ESP/AH. Our code takes care of +the case. + +Basic crypto functions can be found in directory "sys/crypto". ESP/AH +transform are listed in {esp,ah}_core.c with wrapper functions. If you +wish to add some algorithm, add wrapper function in {esp,ah}_core.c, and +add your crypto algorithm code into sys/crypto. + +Tunnel mode is partially supported in this release, with the following +restrictions: +- IPsec tunnel is not combined with GIF generic tunneling interface. + It needs a great care because we may create an infinite loop between + ip_output() and tunnelifp->if_output(). Opinion varies if it is better + to unify them, or not. +- MTU and Don't Fragment bit (IPv4) considerations need more checking, but + basically works fine. +- Authentication model for AH tunnel must be revisited. We'll need to + improve the policy management engine, eventually. + +4.4 Conformance to RFCs and IDs + +The IPsec code in the kernel conforms (or, tries to conform) to the +following standards: + "old IPsec" specification documented in rfc182[5-9].txt + "new IPsec" specification documented in rfc240[1-6].txt, rfc241[01].txt, + rfc2451.txt and draft-mcdonald-simple-ipsec-api-01.txt (draft expired, + but you can take from ftp://ftp.kame.net/pub/internet-drafts/). + (NOTE: IKE specifications, rfc241[7-9].txt are implemented in userland, + as "racoon" IKE daemon) + +Currently supported algorithms are: + old IPsec AH + null crypto checksum (no document, just for debugging) + keyed MD5 with 128bit crypto checksum (rfc1828.txt) + keyed SHA1 with 128bit crypto checksum (no document) + HMAC MD5 with 128bit crypto checksum (rfc2085.txt) + HMAC SHA1 with 128bit crypto checksum (no document) + old IPsec ESP + null encryption (no document, similar to rfc2410.txt) + DES-CBC mode (rfc1829.txt) + new IPsec AH + null crypto checksum (no document, just for debugging) + keyed MD5 with 96bit crypto checksum (no document) + keyed SHA1 with 96bit crypto checksum (no document) + HMAC MD5 with 96bit crypto checksum (rfc2403.txt + HMAC SHA1 with 96bit crypto checksum (rfc2404.txt) + new IPsec ESP + null encryption (rfc2410.txt) + DES-CBC with derived IV + (draft-ietf-ipsec-ciph-des-derived-01.txt, draft expired) + DES-CBC with explicit IV (rfc2405.txt) + 3DES-CBC with explicit IV (rfc2451.txt) + BLOWFISH CBC (rfc2451.txt) + CAST128 CBC (rfc2451.txt) + RC5 CBC (rfc2451.txt) + each of the above can be combined with: + ESP authentication with HMAC-MD5(96bit) + ESP authentication with HMAC-SHA1(96bit) + +The following algorithms are NOT supported: + old IPsec AH + HMAC MD5 with 128bit crypto checksum + 64bit replay prevention + (rfc2085.txt) + keyed SHA1 with 160bit crypto checksum + 32bit padding (rfc1852.txt) + +IPsec (in kernel) and IKE (in userland as "racoon") has been tested +at several interoperability test events, and it is known to interoperate +with many other implementations well. Also, KAME IPsec has quite wide +coverage for IPsec crypto algorithms documented in RFC (we cover +algorithms without intellectual property issues only). + +4.5 ECN consideration on IPsec tunnels + +KAME IPsec implements ECN-friendly IPsec tunnel, described in +draft-ipsec-ecn-00.txt. +Normal IPsec tunnel is described in RFC2401. On encapsulation, +IPv4 TOS field (or, IPv6 traffic class field) will be copied from inner +IP header to outer IP header. On decapsulation outer IP header +will be simply dropped. The decapsulation rule is not compatible +with ECN, since ECN bit on the outer IP TOS/traffic class field will be +lost. +To make IPsec tunnel ECN-friendly, we should modify encapsulation +and decapsulation procedure. This is described in +http://www.aciri.org/floyd/papers/draft-ipsec-ecn-00.txt, chapter 3. + +KAME IPsec tunnel implementation can give you three behaviors, by setting +net.inet.ipsec.ecn (or net.inet6.ipsec6.ecn) to some value: +- RFC2401: no consideration for ECN (sysctl value -1) +- ECN forbidden (sysctl value 0) +- ECN allowed (sysctl value 1) +Note that the behavior is configurable in per-node manner, not per-SA manner +(draft-ipsec-ecn-00 wants per-SA configuration, but it looks too much for me). + +The behavior is summarized as follows (see source code for more detail): + + encapsulate decapsulate + --- --- +RFC2401 copy all TOS bits drop TOS bits on outer + from inner to outer. (use inner TOS bits as is) + +ECN forbidden copy TOS bits except for ECN drop TOS bits on outer + (masked with 0xfc) from inner (use inner TOS bits as is) + to outer. set ECN bits to 0. + +ECN allowed copy TOS bits except for ECN use inner TOS bits with some + CE (masked with 0xfe) from change. if outer ECN CE bit + inner to outer. is 1, enable ECN CE bit on + set ECN CE bit to 0. the inner. + +General strategy for configuration is as follows: +- if both IPsec tunnel endpoint are capable of ECN-friendly behavior, + you'd better configure both end to "ECN allowed" (sysctl value 1). +- if the other end is very strict about TOS bit, use "RFC2401" + (sysctl value -1). +- in other cases, use "ECN forbidden" (sysctl value 0). +The default behavior is "ECN forbidden" (sysctl value 0). + +For more information, please refer to: + http://www.aciri.org/floyd/papers/draft-ipsec-ecn-00.txt + RFC2481 (Explicit Congestion Notification) + KAME sys/netinet6/{ah,esp}_input.c + +(Thanks goes to Kenjiro Cho <kjc@csl.sony.co.jp> for detailed analysis) + +4.6 Interoperability + +Here are (some of) platforms we have tested IPsec/IKE interoperability +in the past. Note that both ends (KAME and others) may have modified their +implementation, so use the following list just for reference purposes. + Altiga, Ashley-laurent (vpcom.com), Data Fellows (F-Secure), Ericsson + ACC, FreeS/WAN, HITACHI, IBM AIX, IIJ, Intel, Microsoft WinNT, NIST + (linux IPsec + plutoplus), Netscreen, OpenBSD, RedCreek, Routerware, + SSH, Secure Computing, Soliton, Toshiba, VPNet, Yamaha RT100i + +5. IPComp +(not yet put into FreeBSD4.x, due to inflate related changes in 4.x.) + +IPComp stands for IP payload compression protocol. This is aimed for +payload compression, not the header compression like PPP VJ compression. +This may be useful when you are using slow serial link (say, cell phone) +with powerful CPU (well, recent notebook PCs are really powerful...). +The protocol design of IPComp is very similar to IPsec. + +KAME implements the following specifications: +- RFC2393: IP Payload Compression Protocol (IPComp) +- RFC2394: IP Payload Compression Using DEFLATE + +Here are some points to be noted: +- IPComp is treated as part of IPsec protocol suite, and SPI and + CPI space is unified. Spec says that there's no relationship + between two so they are assumed to be separate. +- IPComp association (IPCA) is kept in SAD. +- It is possible to use well-known CPI (CPI=2 for DEFLATE for example), + for outbound/inbound packet, but for indexing purposes one element from + SPI/CPI space will be occupied anyway. +- pfkey is modified to support IPComp. However, there's no official + SA type number assignment yet. Portability with other IPComp + stack is questionable (anyway, who else implement IPComp on UN*X?). +- Spec says that IPComp output processing must be performed before IPsec + output processing, to achieve better compression ratio and "stir" data + stream before encryption. However, with manual SPD setting, you are able to + violate the ordering requirement (KAME code is too generic, maybe). +- Though MTU can be significantly decreased by using IPComp, no special + consideration is made about path MTU (spec talks nothing about MTU + consideration). IPComp is designed for serial links, not ethernet-like + medium, it seems. +- You can change compression ratio on outbound packet, by changing + deflate_policy in sys/netinet6/ipcomp_core.c. You can also change history + buffer size by changing deflate_window in the same source code. + (should it be sysctl accessible? or per-SAD configurable?) +- Tunnel mode IPComp is not working right. KAME box can generate tunnelled + IPComp packet, however, cannot accept tunneled IPComp packet. + +6. ALTQ + (not yet put into FreeBSD4.x) + + <end of IMPLEMENTATION> |