FW: Simple dual homing experiment

["Christian Huitema" <huitema@windows.microsoft.com>]

Kurtis,

David and I wrote up a "simple dual homing" proposal, based on previous drafts and private conversations. This may be one of several ways of going forward in multi6.

-- Christian Huitema


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\fs24\lang1033\langfe1033\cgrid\langnp1033\langfenp1033 {\insrsid10837392\charrsid526897 Christian}{\insrsid10837392  Huitema}{\insrsid14700229  , David Kessens}{\insrsid10837392 \line  \par {\listtext\pard\plain\s1 \f35\fs36 \hich\af35\dbch\af0\loch\f35 1\tab}}\pard\plain \s1\ql \fi-432\li432\ri0\nowidctlpar\jclisttab\tx432\faauto\ls7\outlinelevel0\rin0\lin432\itap0\pararsid14700229  \f35\fs36\lang1033\langfe1033\cgrid\langnp1033\langfenp1033 {\insrsid10837392 Simple dual homing problem statement \par }\pard\plain \ql \li0\ri0\widctlpar\aspalpha\aspnum\faauto\adjustright\rin0\lin0\itap0\pararsid14700229 \fs24\lang1033\langfe1033\cgrid\langnp1033\langfenp1033 {\insrsid14700229  In order to make progress towards an IPv6 site multi-homing solution, we propose to start with a simple problem: how to multi-home the simplest site, i.e. a site composed of a single link, e.g. a switched Ethernet network.}{\insrsid10837392  \par }{\insrsid14700229  \par We believe that addressing the problem of simple, small networks is both urgent and useful. Providing a simple solution for the most numerous networks drastically reduces the danger that generalized multi-homing poses to the Internet.  A small network solution may or may not be easily extensible to larger networks, but we know that there are order of magnitude less large networks than small. If we have a solution for the small networks, the scope of the remaining problem will \'93only \'94 be the hundreds of thousands of larger networks, rather than the hundreds of millions of home networks. \par  \par Many small business networks use a simple pattern of multi-homing today: the }{\insrsid4355358 very }{\insrsid14700229 small business network is composed of a switched Ethernet, combining fixed line and wireless links}{\insrsid4355358 ; it connects to the Internet through two independent connections, such as two DSL lines. There is no coordination between the two providers. In a typical IPv4 set-up, each Internet connection terminates in a different NAT/Firewall; one connection is used as back-up, and is turned on if the other connection fails. \par  \par Other examples of this simple multi-homing pattern include home networks connected to a broadband service but also maintaining a dial-up connection for back-up; and home networks connected to two broadband connections such  as DSL and cable, or perhaps wireless services. \par  \par {\listtext\pard\plain\s1 \f35\fs36\insrsid4355358\charrsid4355358 \hich\af35\dbch\af0\loch\f35 2\tab}}\pard\plain \s1\ql \fi-432\li432\ri0\nowidctlpar\jclisttab\tx432\faauto\ls7\outlinelevel0\rin0\lin432\itap0\pararsid4355358  \f35\fs36\lang1033\langfe1033\cgrid\langnp1033\langfenp1033 {\insrsid4355358\charrsid4355358 Define }{\insrsid4355358 a simple set of requirements}{\insrsid4355358\charrsid4355358  \par }\pard\plain \ql \li0\ri0\widctlpar\aspalpha\aspnum\faauto\adjustright\rin0\lin0\itap0\pararsid14700229 \fs24\lang1033\langfe1033\cgrid\langnp1033\langfenp1033 {\insrsid4355358 For the small networks, the basic motivation for multi-homing is redundancy  and reliability. Reliability is defined, as a minimum, as the }{\insrsid71595 possibility to maintain operation in cases}{\insrsid4355358  of failure of one the Internet provider connections.  \par }{\insrsid71595  \par We will expect the site to contain both \'93simple\'94 and \'93smart\'94 hosts. Simple hosts have an implementation of IPv6 conformant to RFC 2641; smart hosts are supposed to be upgraded to become \'93site multi-homing aware\'94. The reliability  expectation is slightly different for the two kinds of hosts. In case of failure of a provider connection, the simple hosts may suffer from a temporary loss of connectivity; the expectation is that operation will shortly resume over the remaining  connection; this matches the expectation of current IPv4 \'93back-up\'94 services. On the contrary, the smart hosts are expected to obtain better services: established TCP-IP connections should survive the loss of one of the provider connections ; if connections cannot be maintained, operation should at least resume immediately; it should be possible to perform some amount of load balancing between the two connections. \par }{\insrsid4355358  \par We assume that it is entirely acceptable that the two Internet providers each allocate a \'93provider aggregated\'94 p}{\insrsid71595 refix to the small site. Simple hosts are expected to auto-configure addresses using at least one of these p refixes; smart hosts are expected to auto-configure addresses using both. It is reasonable to expect that hosts have to be renumbe}{\insrsid14695499 red a fter a connectivity event, although we also expect that addresses configured with one prefix will remain valid as long as this prefix is valid.}{\insrsid4355358  \par }{\insrsid14695499  \par The}{\insrsid10837392  following section details }{\insrsid14695499 specific problems that must be solved by the simple multi-homing solution. \par {\listtext\pard\plain\s1 \f35\fs36\insrsid10837392 \hich\af35\dbch\af0\loch\f35 3\tab}}\pard\plain \s1\ql \fi-432\li432\ri0\nowidctlpar\jclisttab\tx432\faauto\ls7\outlinelevel0\rin0\lin432\itap0\pararsid10837392  \f35\fs36\lang1033\langfe1033\cgrid\langnp1033\langfenp1033 {\insrsid10837392 M}{\insrsid14695499 ulti-homing issues}{\insrsid3560762\charrsid3560762  \par }\pard\plain \ql \li0\ri0\widctlpar\aspalpha\aspnum\faauto\adjustright\rin0\lin0\itap0\pararsid14695499 \fs24\lang1033\langfe1033\cgrid\langnp1033\langfenp1033 {\insrsid10837392 The five}{\insrsid14695499  multihoming issues that we want to solve are ingress filtering, avoidance of a \'93dead connection\'94}{\insrsid10837392  for outbound connections, avoidance of a dead address for inbound connections}{\insrsid14695499 ,  connection maintenance and exit selection.}{\insrsid3560762  We believe that the solution to these problems is in the realm of engineering, not research. For each problem, we give hint of one or several possible solutions. We also believe that relatively  simple solutions are possible, and should be preferred to \'93innovative\'94 constructs.}{\insrsid3560762\charrsid14695499  \par {\listtext\pard\plain\s2 \f35\fs32\insrsid14695499 \hich\af35\dbch\af0\loch\f35 3.1\tab}}\pard\plain \s2\ql \fi-576\li576\ri0\nowidctlpar\jclisttab\tx576\faauto\ls7\ilvl1\outlinelevel1\rin0\lin576\itap0\pararsid14695499  \f35\fs32\lang1033\langfe1033\cgrid\langnp1033\langfenp1033 {\insrsid14695499 I}{\insrsid10837392 ngress filtering \par }\pard\plain \ql \li0\ri0\widctlpar\aspalpha\aspnum\faauto\adjustright\rin0\lin0\itap0\pararsid14695499 \fs24\lang1033\langfe1033\cgrid\langnp1033\langfenp1033 {\insrsid14695499\charrsid14695499 We assume that each of the ISP may perform ingress  filtering, and will reject packets whose source address does not belong to the prefix allocated to the network by that ISP. This leads to a possible failure}{\insrsid10837392\charrsid14695499  scenario}{\insrsid14695499 :}{ \insrsid10837392\charrsid14695499  \par {\listtext\pard\plain\f3\charrsid14695499 \loch\af3\dbch\af0\hich\f3 \'b7\tab}}\pard \ql \fi-360\li720\ri0\widctlpar\jclisttab\tx720\aspalpha\aspnum\faauto\ls8\adjustright\rin0\lin720\itap0\pararsid14695499 {\insrsid10837392\charrsid14695499  Host choose source address A \par {\listtext\pard\plain\f3\charrsid14695499 \loch\af3\dbch\af0\hich\f3 \'b7\tab}Default route leads to router B \par {\listtext\pard\plain\f3\charrsid14695499 \loch\af3\dbch\af0\hich\f3 \'b7\tab}Router B forwards the packet to ISP B \par {\listtext\pard\plain\f3\charrsid14695499 \loch\af3\dbch\af0\hich\f3 \'b7\tab}Packet is dropped by ingress filtering. \par }\pard \ql \li0\ri0\widctlpar\aspalpha\aspnum\faauto\adjustright\rin0\lin0\itap0\pararsid14695499 {\insrsid14695499 The multi-homing proposal must present a solution to this problem.  We believe that this solution can be engineered by simple improvements in the small site exit routers, such as }{\insrsid10837392\charrsid14695499 check}{\insrsid14695499 ing the}{\insrsid10837392\charrsid14695499  source address}{\insrsid14695499  of the Internet bound packets and}{\insrsid10837392\charrsid14695499  redirect}{\insrsid14695499 ing these}{\insrsid10837392\charrsid14695499  packet}{\insrsid14695499 s}{\insrsid10837392\charrsid14695499  to }{\insrsid14695499 the }{ \insrsid10837392\charrsid14695499 \'93right\'94 }{\insrsid14695499 exit }{\insrsid10837392\charrsid14695499 router in case of problem}{\insrsid14695499 . This solution should not depend on any particular host behavior, beyond what i s mandated by RFC 2641; however, smart hosts may improve on the basic solution, e.g. by}{\insrsid10837392\charrsid14695499  select}{\insrsid14695499 ing a next hop exit}{\insrsid10837392\charrsid14695499  router }{\insrsid14695499  as a function of the source address.}{\insrsid10837392\charrsid14695499  \par {\listtext\pard\plain\s2 \f35\fs32\insrsid526897 \hich\af35\dbch\af0\loch\f35 3.2\tab}}\pard\plain \s2\ql \fi-576\li576\ri0\nowidctlpar\jclisttab\tx576\faauto\ls7\ilvl1\outlinelevel1\rin0\lin576\itap0\pararsid526897  \f35\fs32\lang1033\langfe1033\cgrid\langnp1033\langfenp1033 {\insrsid526897 A}{\insrsid10837392 void using dead router}{\insrsid10837392  for outbound connections}{\insrsid10837392  \par }\pard\plain \ql \li0\ri0\widctlpar\aspalpha\aspnum\faauto\adjustright\rin0\lin0\itap0\pararsid526897 \fs24\lang1033\langfe1033\cgrid\langnp1033\langfenp1033 {\insrsid526897 The purpose of multi-homing is to provide redundancy, and to avoid the following  f}{\insrsid10837392\charrsid526897 ailure scenario}{\insrsid526897 :}{\insrsid10837392\charrsid526897  \par {\listtext\pard\plain\f3\charrsid526897 \loch\af3\dbch\af0\hich\f3 \'b7\tab}}\pard \ql \fi-360\li720\ri0\widctlpar\jclisttab\tx720\aspalpha\aspnum\faauto\ls9\adjustright\rin0\lin720\itap0\pararsid526897 {\insrsid10837392\charrsid526897  Router A is dead, or link to ISP A is dead \par {\listtext\pard\plain\f3\charrsid526897 \loch\af3\dbch\af0\hich\f3 \'b7\tab}Host continue sending using source address A \par {\listtext\pard\plain\f3\insrsid526897 \loch\af3\dbch\af0\hich\f3 \'b7\tab}}{\insrsid526897 Because of ingress filtering, r}{\insrsid10837392\charrsid526897 outer B cannot forward the packets \par }\pard \ql \li0\ri0\widctlpar\aspalpha\aspnum\faauto\adjustright\rin0\lin0\itap0\pararsid526897 {\insrsid526897 The multi-homing proposal must present a solution to this problem, and the solution must work for both simple hosts and smart hosts. We believe that a solution can be engineered by an appropriate use of \'93router announce\'94 messages, such as stopping advertisement of a prefix if the connection is unavailable, or possibly advertising this prefix as \'93deprecated.\'94 }{\insrsid10837392\charrsid526897 Smart host}{\insrsid526897  may improve on that solution by implementing detecting the loss of connectivity independently of the router advertisements, and automatically preferring the other }{\insrsid10837392\charrsid526897 address}{\insrsid526897  for new connections.}{\insrsid10837392  \par {\listtext\pard\plain\s2 \f35\fs32\insrsid10837392 \hich\af35\dbch\af0\loch\f35 3.3\tab}}\pard\plain \s2\ql \fi-576\li576\ri0\nowidctlpar\jclisttab\tx576\faauto\ls7\ilvl1\outlinelevel1\rin0\lin576\itap0\pararsid10837392  \f35\fs32\lang1033\langfe1033\cgrid\langnp1033\langfenp1033 {\insrsid10837392 Avoid using dead address for outbound connections \par }\pard\plain \ql \li0\ri0\widctlpar\aspalpha\aspnum\faauto\adjustright\rin0\lin0\itap0\pararsid10837392 \fs24\lang1033\langfe1033\cgrid\langnp1033\langfenp1033 {\insrsid10837392 A variation of the previous f}{\insrsid10837392\charrsid526897  ailure scenario}{\insrsid10837392  occurs when a service is hosted on the small network:}{\insrsid10837392\charrsid526897  \par {\listtext\pard\plain\f3\insrsid10837392 \loch\af3\dbch\af0\hich\f3 \'b7\tab}}\pard \ql \fi-360\li720\ri0\widctlpar\jclisttab\tx720\aspalpha\aspnum\faauto\ls9\adjustright\rin0\lin720\itap0\pararsid10837392 {\insrsid10837392  Service advertises both address A and address B in the DNS \par {\listtext\pard\plain\f3\insrsid10837392\charrsid526897 \loch\af3\dbch\af0\hich\f3 \'b7\tab}}{\insrsid10837392\charrsid526897 Router A is dead, or link to ISP A is dead \par {\listtext\pard\plain\f3\insrsid10837392 \loch\af3\dbch\af0\hich\f3 \'b7\tab}}{\insrsid10837392 A remote client selects }{\insrsid10837392\charrsid526897 address A}{\insrsid10837392  to reach the service}{\insrsid10837392\charrsid526897  \par {\listtext\pard\plain\f3\insrsid10837392 \loch\af3\dbch\af0\hich\f3 \'b7\tab}}{\insrsid10837392 The connection fails}{\insrsid10837392\charrsid526897  \par }\pard \ql \li0\ri0\widctlpar\aspalpha\aspnum\faauto\adjustright\rin0\lin0\itap0\pararsid10837392 {\insrsid10837392 The multi-homing proposal must present a solution to this problem, and the solution must work for both simple hosts and smart hosts. A possible solution is to expect remote hosts to retry the connection attempt using the second address; another solution is to somehow update the DNS.}{\insrsid10837392\charrsid526897  \par {\listtext\pard\plain\s2 \f35\fs32\insrsid526897 \hich\af35\dbch\af0\loch\f35 3.4\tab}}\pard\plain \s2\ql \fi-576\li576\ri0\nowidctlpar\jclisttab\tx576\faauto\ls7\ilvl1\outlinelevel1\rin0\lin576\itap0\pararsid526897  \f35\fs32\lang1033\langfe1033\cgrid\langnp1033\langfenp1033 {\insrsid526897 M}{\insrsid10837392 aintain}{\insrsid526897 ing}{\insrsid10837392  connection}{\insrsid526897 s}{\insrsid10837392  \par }\pard\plain \ql \li0\ri0\widctlpar\aspalpha\aspnum\faauto\adjustright\rin0\lin0\itap0\pararsid526897 \fs24\lang1033\langfe1033\cgrid\langnp1033\langfenp1033 {\insrsid526897 Solving the  ingress filtering and dead router problem provides small site with a functional multi-homing solution, but does not resolve the following f}{\insrsid10837392\charrsid526897 ailure scenario}{\insrsid526897 :}{\insrsid10837392\charrsid526897  \par {\listtext\pard\plain\f3\charrsid526897 \loch\af3\dbch\af0\hich\f3 \'b7\tab}}\pard \ql \fi-360\li720\ri0\widctlpar\jclisttab\tx720\aspalpha\aspnum\faauto\ls10\adjustright\rin0\lin720\itap0\pararsid526897 {\insrsid10837392\charrsid526897  Host has connection with peer P using address A \par {\listtext\pard\plain\f3\charrsid526897 \loch\af3\dbch\af0\hich\f3 \'b7\tab}Router A or ISP A fails \par {\listtext\pard\plain\f3\charrsid526897 \loch\af3\dbch\af0\hich\f3 \'b7\tab}Existing connections break \par }\pard \ql \li0\ri0\widctlpar\aspalpha\aspnum\faauto\adjustright\rin0\lin0\itap0\pararsid526897 {\insrsid526897 We accept the loss of connections in the case of the simple hosts; the simple hosts will simply have to reestablish their connectio ns. However, the mult}{\insrsid3560762 i-homing proposal should provide smart hosts with}{\insrsid526897  a solution }{\insrsid3560762 to this problem. We believe that it is possible to engineer this solution by using a variation of Mobile IPv6.}{ \insrsid10837392\charrsid526897  \par {\listtext\pard\plain\s2 \f35\fs32\insrsid3560762 \hich\af35\dbch\af0\loch\f35 3.5\tab}}\pard\plain \s2\ql \fi-576\li576\ri0\nowidctlpar\jclisttab\tx576\faauto\ls7\ilvl1\outlinelevel1\rin0\lin576\itap0\pararsid3560762  \f35\fs32\lang1033\langfe1033\cgrid\langnp1033\langfenp1033 {\insrsid3560762 U}{\insrsid10837392 se the right exit/entrance \par }\pard\plain \ql \li0\ri0\widctlpar\aspalpha\aspnum\faauto\adjustright\rin0\lin0\itap0\pararsid3560762 \fs24\lang1033\langfe1033\cgrid\langnp1033\langfenp1033 {\insrsid3560762  Even if we are able to provide redundancy and reliability, the dual homed networks are still exposed to the following f}{\insrsid10837392\charrsid3560762 ailure mode}{\insrsid3560762 :}{\insrsid10837392\charrsid3560762  \par {\listtext\pard\plain\f3\charrsid3560762 \loch\af3\dbch\af0\hich\f3 \'b7\tab}}\pard \ql \fi-360\li720\ri0\widctlpar\jclisttab\tx720\aspalpha\aspnum\faauto\ls11\adjustright\rin0\lin720\itap0\pararsid3560762 {\insrsid10837392\charrsid3560762  Peer picks address A rather than address B \par {\listtext\pard\plain\f3\charrsid3560762 \loch\af3\dbch\af0\hich\f3 \'b7\tab}Resulting traffic }{\insrsid3560762 is }{\insrsid10837392\charrsid3560762 routed }{\insrsid3560762 on a slower path or on a congested connection}{ \insrsid10837392\charrsid3560762  \par {\listtext\pard\plain\f3\charrsid3560762 \loch\af3\dbch\af0\hich\f3 \'b7\tab}Performance looks terrible \par }\pard \ql \li0\ri0\widctlpar\aspalpha\aspnum\faauto\adjustright\rin0\lin0\itap0\pararsid3560762 {\insrsid3560762 The multi-homing proposal should provide a solution to this problem, and this solution should be available at least to smart hosts.  The goal is not to obtain an absolute optimization of network usage, but rather to avoid the most obnoxious results of load imbalance. We believe that it is possible to engineer a solution  using either a smart naming service (a.k.a. DNS load balancing), a routing level optimization such as a randomized choice of exit routers, or possibly a variation of Mobile IPv6 to move existing connections towards a less loaded path.}{ \insrsid10837392\charrsid3560762  \par {\listtext\pard\plain\s1 \f35\fs32 \hich\af35\dbch\af0\loch\f35 4\tab}}\pard\plain \s1\ql \fi-432\li432\ri0\nowidctlpar\jclisttab\tx432\faauto\ls7\outlinelevel0\rin0\lin432\itap0 \f35\fs36\lang1033\langfe1033\cgrid\langnp1033\langfenp1033 { \fs32\insrsid10837392 Further study \par }\pard\plain \ql \li0\ri0\widctlpar\aspalpha\aspnum\faauto\adjustright\rin0\lin0\itap0\pararsid11022224 \fs24\lang1033\langfe1033\cgrid\langnp1033\langfenp1033 {\insrsid11022224 The goal of the simple dual homing exercise is to provide a simpl e solution to the simple sites. Once this goal is achieved, we believe that the solution can be extended in two directions: extend the solution to medium size sites; and extend the solution to accommodate a form of provider independent addressing.  \par  \par The extension to medium size sites can be thought as a progress on a scale of complexity: first, extend the solution to multilink subnets, where }{\insrsid10837392\charrsid11022224 all exit routers }{\insrsid11022224 are }{ \insrsid10837392\charrsid11022224 on }{\insrsid11022224 the same link; second, extend the solution to }{\insrsid10837392\charrsid11022224 routed network,}{\insrsid11022224  where}{\insrsid10837392\charrsid11022224  all exit routers }{\insrsid11022224 are  }{\insrsid10837392\charrsid11022224 on }{\insrsid11022224 the same link; and third, extend the solution to }{\insrsid10837392\charrsid11022224 routed network, }{\insrsid11022224 where exit routers are present at}{\insrsid10837392\charrsid11022224  different location}{\insrsid11022224 s.}{\insrsid10837392  \par }{\insrsid11022224  \par Provider independent addressing is often used today by large IPv4 sites, which simply obtain a prefix form a registry, use this prefix for internal addresses, and insure that the pre fix is distributed in the global routing tables. We believe that similar solutions will be available for large IPv6 sites, but we are also very aware that they cannot be extended to the majority of smaller IPv6 sites. Yet, the small IPv6 sites may benefit from some form of provider independent addresses, e.g. in order to advertise addresses that don\rquote t depend on a particular provider configuration. It may be possible for these sites to use a \'93virtual IP\'94 solution, in which connectivity through a PI address is overlaid on top of the regular provider based addressing. This can be thought of as an extension of the simple solution.}{\insrsid11022224\charrsid11022224  \par }{\insrsid10837392  \par }{\insrsid10837392\charrsid11022224  \par }}