RFC 4191

Default Router Preferences and More-Specific Routes

📅 published November 2005, from ietf

RFC 4191: Default Router Preferences and More-Specific Routes 🎀

Okay bestie, this one is a Standards Track doc from the Network Working Group, written by R. Draves and D. Thaler at Microsoft, dated November 2005. It doesn't list any RFCs it obsoletes or updates, so it's standing on its own. 💅

Status of This Memo 📜

This document specifies an Internet standards track protocol for the Internet community, and it's asking for discussion and suggestions for improvements. For the standardization state and status of this protocol, check the current edition of the "Internet Official Protocol Standards" (STD 1). Distribution of this memo is unlimited. ✨

Copyright Notice 🌸

Abstract 🦋

So this doc describes an optional extension to Router Advertisement messages. It lets routers tell hosts about default router preferences and more-specific routes. The point is that hosts get way better at picking a good router, especially when the host is multi-homed and its routers sit on different links 🔥. The preference values and specific routes sent to hosts need administrative configuration. They are NOT automatically pulled from routing tables, so no sneaky auto-magic here 🙈.

1. Introduction ✨

Okay so, Neighbor Discovery [RFC2461] gives us a conceptual model for hosts, and it includes a Default Router List and a Prefix List 📋. Hosts send Router Solicitation messages and receive Router Advertisement messages from routers. They fill up their Default Router List and Prefix List using info from those Router Advertisements. The sending algorithm checks the Prefix List to see if a destination is on-link, and it checks the Default Router List to pick a router for off-link destinations 🧚.

Here's the thing: when a host has several routers on its Default Router List, which one it picks for an off-link destination really matters 😭. One router might be way faster for a given destination. Picking the wrong one could mean the host just can't talk to that destination at all. (Section 5 has specific examples of these scenarios.) So this document adds an optional extension to Neighbor Discovery Router Advertisement messages. Routers use it to tell hosts about default router preferences and more-specific routes, which helps hosts choose a good router for an off-link destination 💜.

Also, these procedures only apply to hosts. The forwarding algorithm that routers use (including hosts with IP forwarding turned on) is not affected 🫶.

Neighbor Discovery already has a Redirect message that routers can use to fix a host's router choice. A router can send a Redirect to a host and say "use a different router for this specific destination." The catch is that Redirect only works on a single link. A router on one link can't redirect a host to a router on another link. So Redirect doesn't help multi-homed hosts (hosts with multiple interfaces) pick a good router 🙃.

Multi-homed hosts are a bigger deal every day, especially with IPv6 🌈. Besides a wired connection like Ethernet, a host might have wireless connections like 802.11 or Bluetooth. Besides physical connections, it might have virtual or tunnel connections too. For example, a host might connect directly to the public Internet AND have a tunnel into a private corporate network. Some IPv6 transition setups add even more tunnels. Hosts might have 6to4 [RFC3056] or configured tunnel [RFC2893] connections 🦋.

This document says the preference values and specific routes sent to hosts REQUIRE explicit administrative configuration. Again, they are not automatically derived from routing tables 🛑. Also, the preference values are NOT routing metrics, and routers are not recommended to "dump out" their entire routing tables to hosts. Totally not the vibe 💀.

Why Router Advertisements and not something like RIP [RFC2080]? Router Advertisements are already an existing, stable standard protocol for router-to-host communication 👑. Piggybacking this info onto message traffic that's already going from routers to hosts keeps network overhead down. Neighbor Discovery and Multicast Listener Discovery both define host-to-router interactions, and they keep the host from having to deal with general router-to-router stuff 🎀. RIP is a no-go too, because it doesn't carry route lifetimes, so it needs frequent message traffic and has heavier processing overhead 😩.

The mechanisms here are backwards-compatible. Hosts that don't implement them keep working just as well as they did before 🫶✨.

1.1. Conventions Used in This Document 📝

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. Iykyk 🤓.

2. Message Formats 🎀

2.1. Preference Values 💖

Default router preferences and preferences for more-specific routes are encoded the SAME way 🧚.

Preference values are a two-bit signed integer, laid out like this:

01      High
00      Medium (default)
11      Low
10      Reserved - MUST NOT be sent

Note that implementations can treat the value as a two-bit signed integer 🔢.

Having just three values is lowkey the point. It reinforces that they're not metrics, and more values just aren't needed for reasonable scenarios 💅.

2.2. Changes to Router Advertisement Message Format 🌸

Here's what changes from Neighbor Discovery [RFC2461] Section 4.2 and [RFC3775] Section 7.1 ✨:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |     Code      |          Checksum             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Cur Hop Limit |M|O|H|Prf|Resvd|       Router Lifetime         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Reachable Time                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Retrans Timer                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Options ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-

Fields:

Prf (Default Router Preference) 🌈 : 2-bit signed integer. It says whether to prefer this router over other default routers. If the Router Lifetime is zero, the preference value MUST be set to (00) by the sender and MUST be ignored by the receiver. If the Reserved (10) value gets received, the receiver MUST treat the value as if it were (00). ⚠️

Resvd (Reserved) 🍓 : A 3-bit unused field. It MUST be initialized to zero by the sender and MUST be ignored by the receiver.

Possible Options:

Route Information 🗺️ : These options specify prefixes that are reachable via the router.

Discussion:

Okay so a Router Advertisement can contain a Route Information Option for ::/0, with its own preference value and lifetime. But encoding a preference value in the Router Advertisement header has some perks 🎀:

It lets you tell apart the "best router for the default route" from the "router least likely to redirect common traffic," as described below in Section 5.1. Two different vibes, so you need two different answers 👑.
When the best router for the default route is ALSO the router least likely to redirect common traffic (which will be a common case 💅), putting the preference value in the message header is more efficient than sending a separate option ⚡.

2.3. Route Information Option 🦋

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |    Length     | Prefix Length |Resvd|Prf|Resvd|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Route Lifetime                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Prefix (Variable Length)                    |
   .                                                               .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Fields:

Type 🔖 : 24

Length 📏 : 8-bit unsigned integer. The length of the option (including the Type and Length fields) in units of 8 octets. The Length field is 1, 2, or 3 depending on the Prefix Length. If Prefix Length is greater than 64, then Length must be 3. If Prefix Length is greater than 0, then Length must be 2 or 3. If Prefix Length is zero, then Length must be 1, 2, or 3.

Prefix Length 🔢 : 8-bit unsigned integer. The number of leading bits in the Prefix that are valid. The value ranges from 0 to 128. The Prefix field is 0, 8, or 16 octets depending on Length.

Prf (Route Preference) 🌟 : 2-bit signed integer. The Route Preference says whether to prefer the router associated with this prefix over others, when multiple identical prefixes (for different routers) have been received. If the Reserved (10) value is received, the Route Information Option MUST be ignored. 🚫

Resvd (Reserved) 🍓 : Two 3-bit unused fields. They MUST be initialized to zero by the sender and MUST be ignored by the receiver.

Route Lifetime ⏳ : 32-bit unsigned integer. The length of time in seconds (relative to the time the packet is sent) that the prefix is valid for route determination. A value of all one bits (0xffffffff) represents infinity. ♾️

Prefix 🧭 : Variable-length field containing an IP address or a prefix of an IP address. The Prefix Length field contains the number of valid leading bits in the prefix. The bits in the prefix after the prefix length (if any) are reserved and MUST be initialized to zero by the sender and ignored by the receiver.

Routers MUST NOT include two Route Information Options with the same Prefix and Prefix Length in the same Router Advertisement. No duplicates, periodt 🙅‍♀️.

Discussion:

There are a few reasons this uses a NEW Route Information Option instead of flag bits overloading the existing Prefix Information Option 🤔:

Prefixes will typically only show up in one option, not both, so a new option doesn't introduce duplication. No double-dipping 💅.
The Route Information Option is typically 16 octets, while the Prefix Information Option is 32 octets. Smaller is cuter 🧁.
Using a new option may improve backwards-compatibility with some host implementations. Win-win 🫶✨.

3. Conceptual Model of a Host ✨

okay so there are three possible conceptual models for how a host can handle default router preferences and more-specific routes 🧚 they're called type A, type B, and type C, and each one has a different level of support 💅

3.1. Conceptual Data Structures for Hosts

type A hosts totally ignore default router preferences and more-specific routes 🙈 they just use the conceptual data structures from Neighbor Discovery [RFC2461] and that's it, no drama

type B hosts use a Default Router List that's been upgraded with preference values, but they ignore all Route Information Options 🎀 they use the Default Router Preference value in the Router Advertisement header, and they ignore Route Information Options (yes, we're saying it twice because it matters 😭)

type C hosts use a Routing Table instead of a Default Router List 👑 (the Routing Table may also subsume the Prefix List too, but that's beyond the scope of this document 🌸) each entry in the Routing Table has a prefix, prefix length, preference value, lifetime, and next-hop router 💖 type C hosts use both the Default Router Preference value in the Router Advertisement header AND Route Information Options, so they're the most in tune 🫶

when a type C host gets a Router Advertisement, it updates its Routing Table like this ✨ first it updates a ::/0 route based on the Router Lifetime and Default Router Preference in the Router Advertisement message header 💅 then, as it works through the Route Information Options in the Router Advertisement message body, it updates its routing table for each one 🦋 the Router Preference and Lifetime values in a ::/0 Route Information Option override the preference and lifetime values in the Router Advertisement header, so that option wins, periodt 👑 updating each route goes like this: a route gets located in the Routing Table based on its prefix, prefix length, and next-hop router 🔥 if the received route's lifetime is zero, the route gets removed from the Routing Table if it's there 💀 if a route's lifetime is non-zero, it gets added to the Routing Table if it isn't there yet, and if it's already there, its lifetime and preference get updated 🌈

here's an example to make it click 🍓 say hosts get a Router Advertisement from router X with a Router Lifetime of 100 seconds and a Default Router Preference of Medium. the body of that Router Advertisement has a Route Information Option for ::/0 with a Route Lifetime of 200 seconds and a Route Preference of Low. after processing it, a type A host has an entry for router X in its Default Router List with a lifetime of 100 seconds 🙈 a type B host that gets the same Router Advertisement has an entry for router X in its Default Router List with a Medium preference and a lifetime of 100 seconds 🫶 and a type C host has an entry in its Routing Table for ::/0 -> router X, with a Low preference and a lifetime of 200 seconds 💜 bestie, the type C host MAY have a transient state while it's processing the Router Advertisement, where it has an entry in its Routing Table for ::/0 -> router X with a Medium preference and a lifetime of 100 seconds 😭✨

3.2. Conceptual Sending Algorithm for Hosts

type A hosts use the conceptual sending algorithm from Neighbor Discovery [RFC2461] 🌸

when a type B host does next-hop determination and checks its Default Router List, it primarily prefers reachable routers over non-reachable ones 🦋 and it secondarily uses the router preference values 💅 if the host has no info about a router's reachability, it assumes the router is reachable 🎀

when a type C host does next-hop determination for an off-link destination, it searches its Routing Table for the route with the longest prefix that matches the destination 🔥 if multiple matching routes have the same prefix length, route preference values act as the tie-breaker 👑 if the best route points to a non-reachable router, that router gets remembered for the algorithm in Section 3.5 below, and then the next best route gets checked 🧚 this keeps going until it finds a matching route that points to a reachable router, or there are no matching routes left 🌈 again, if the host has no info about the router's reachability, it assumes the router is reachable 💖

if there are no routes matching the destination (so no default routes and no more-specific routes), then a type C host SHOULD discard the packet and report a Destination Unreachable/No Route To Destination error to the upper layer 💀

3.3. Destination Cache Management

when a type C host processes a Router Advertisement and updates its conceptual Routing Table, it MUST invalidate or remove Destination Cache Entries and redo next-hop determination for destinations affected by the Routing Table changes 🫶 this is non-negotiable, bestie 🔥

3.4. Client Configurability

type B and C hosts MAY be configurable with preference values that override the values in the Router Advertisements they receive 🎀 this is especially useful for dealing with routers that may not support preferences 🌸

3.5. Router Reachability Probing

when a host avoids using any non-reachable router X and instead sends a data packet to another router Y, and the host would have used router X if it were reachable, then the host SHOULD probe each such router X's reachability by sending a single Neighbor Solicitation to that router's address 🦋 a host MUST NOT probe a router's reachability in the absence of useful traffic that the host would have sent to the router if it were reachable 🙈 and in any case, these probes MUST be rate-limited to no more than one per minute per router ⏰

this requirement lets the host find out when router X becomes reachable and start using it again right then ✨ otherwise, the host might never notice router X is back and keep using the less-desirable router Y until the next Router Advertisement from X 😭 and ngl, the router may have been unreachable for reasons other than being down (like a switch in the middle being down 💀), so it could be up to 30 minutes (the maximum advertisement period) before the next Router Advertisement gets sent 🧚

for a type A host (following the algorithm in [RFC2461]), no probing is needed since all routers are equally preferable 🌈 a type B or C host, on the other hand, explicitly probes unreachable, preferable routers to notice when they become reachable again 💅

3.6. Example

okay picture a type C host with four entries in its Routing Table 🎀

::/0 -> router W with a Medium preference
2002::/16 -> router X with a Medium preference
2001:db8::/32-> router Y with a High preference
2001:db8::/32-> router Z with a Low preference

and the host is sending to 2001:db8::1, an off-link destination 🦋 if all routers are reachable, the host chooses router Y 👑 if router Y isn't reachable, router Z gets chosen and the reachability of router Y gets probed 🫶 if routers Y and Z aren't reachable, router W gets chosen and the reachability of routers Y and Z gets probed 🌸 if routers W, Y, and Z are all not reachable, then the host should use Y while probing the reachability of W and Z 🔥 and router X will never be chosen, because its prefix doesn't match the destination 💀

4. Router Configuration ✨

routers SHOULD NOT advertise preferences or routes by default 🙅‍♀️ like, in particular, they SHOULD NOT "dump out" their entire routing table to hosts 😭

routers MAY have a configuration mode where an announcement of a specific prefix depends on a specific condition, like the operational status of a link or the presence of the same or another prefix in the routing table installed by another source (such as a dynamic routing protocol) 🧚 if that's done, router implementations SHOULD make sure that announcing prefixes to hosts is decoupled from the routing table dynamics, so hosts don't get flooded during periods of routing instability 🌈 in particular, unstable routes SHOULD NOT be announced to hosts until their stability has improved 🫶

routers SHOULD NOT send more than 17 Route Information Options in Router Advertisements per link 🎀 this arbitrary bound is there to reinforce that relatively few and carefully selected routes should be advertised to hosts 💅

the preference values (both Default Router Preferences and Route Preferences) SHOULD NOT be routing metrics or automatically derived from metrics; the preference values SHOULD be configured 🔥

the information in Router Advertisements may change through the actions of system management 🦋 for instance, the lifetime or preference of advertised routes may change, or new routes could be added 🌸 in those cases, the router MAY transmit up to MAX_INITIAL_RTR_ADVERTISEMENTS unsolicited advertisements, using the same rules as in [RFC2461] 💖 and when a router stops being an advertising interface and sends Router Advertisements with a Router Lifetime of zero, the Router Advertisement SHOULD also set the Route Lifetime to zero in all Route Information Options 💀

4.1. Guidance to Administrators

the High and Low (non-default) preference values should only be used when someone with knowledge of both routers and the network topology configures them explicitly 🧠 for example, it could be a common network administrator, or it could be a customer request to different administrators managing the routers 🎀

as one exception to this general rule, the administrator of a router that doesn't have a connection to the Internet (or is connected through a firewall that blocks general traffic) should configure the router to advertise a Low Default Router Preference 🔥

in addition, the administrator of a router should configure the router to advertise a specific route for the site prefix of the network(s) the router belongs to 🌈 the administrator may also configure the router to advertise specific routes for directly connected subnets and any shorter prefixes for networks the router belongs to 🧚

for example, say a home user sets up a tunnel into a firewalled corporate network 🏠 the access router on the corporate end of the tunnel should advertise itself as a default router, but with a Low preference 🫶 and the corporate router should also advertise a specific route for the corporate site prefix 👑 the net result is that corporate destinations get reached via the tunnel, and general Internet destinations get reached via the home ISP ✨ without these mechanisms, the home machine might send Internet traffic into the corporate network, or corporate traffic into the Internet, and that leads to communication failure because of the firewall 😭💀

it's worth noting that the network administrator setting up preferences and/or more specific routes in Routing Advertisements typically doesn't know which kinds of nodes (Type A, B, and/or C) will be connected to its links 🙈 this means the administrator has to configure settings that work optimally no matter which kinds of nodes get attached 💅 two examples of how to do so follow 🎀

5. Examples ✨

5.1. Best Router for `::/0` vs Router Least Likely to Redirect

okay so the best router for the default route (::/0) is the one with the best path out to the wider Internet 🌍✨ but the router least likely to redirect depends on what traffic people are actually sending 💅 and those two can totally be different bestie! 🫶 It happens when most of the traffic really needs to go through some other router.

Picture this: a link with two routers, X and Y 🎀 Router X is the best for 2002::/16 (it's your 6to4 site gateway, so iconic 🦋). Router Y is the best for ::/0 (it connects to the native IPv6 Internet 🌸). Router X forwards native IPv6 traffic to router Y, and router Y forwards 6to4 traffic to router X, so they're literally passing things back and forth 😭 If most of the traffic from this site is headed to 2002:/16 destinations, then router X is the one least likely to redirect 👑

To make type A hosts work well, both routers should advertise themselves as default routers 💖 Especially, if router Y goes down, type A hosts should send traffic to router X to keep 6to4 connectivity alive, so router X and router Y both need to be default routers 🫶

To make type B hosts work well, router X should advertise itself with a High default router preference ✨ That way type B hosts prefer router X, and the number of redirects drops 🍓

To make type C hosts work well, router X should also advertise the ::/0 route with a Low preference and the 2002::/16 route with a Medium preference 🧚 A type C host ends up with three routes in its routing table, and this is the lineup 💅

::/0 -> router X (Low)
::/0 -> router Y (Medium)
2002::/16 -> router X (Medium)

So it sends 6to4 traffic to router X and everything else to router Y, and type C hosts won't cause any redirects at all 🙈✨

Now, a plot twist 🌈 When type C hosts process the Router Advertisement from router X, the Low preference for ::/0 overrides the High default router preference 😭 If the ::/0 specific route weren't there, then a type C host would apply the High default router preference to its ::/0 route to router X instead 🎀

5.2. Multi-Homed Host and Isolated Network

Next up, a multi-homed host 🧚 It's connected to the Internet through router X on one link and to an isolated network through router Y on another link. Maybe it has a tunnel into a firewalled corporate network, or maybe it's plugged straight into an isolated test network 🔥

In this situation, a type A multi-homed host (the one with no default router preferences and no more-specific routes) has no way to pick smartly between routers X and Y on its Default Router List 💀 So users of the host see unpredictable connectivity failures, depending on the destination address and which router got picked 😭

If the routers are set up properly, a multi-homed type B host in this same situation has stable Internet connectivity 🌸 but no connectivity to the isolated test network 🥲

If the routers are set up properly, a multi-homed type C host in this same situation can correctly choose between routers X and Y ✨👑 For example, router Y on the isolated network should advertise a Route Information Option for the isolated network prefix 🦋 It might not advertise itself as a default router at all (zero Router Lifetime), or it might advertise itself as a default router with a Low preference 💜 Router X should advertise itself as a default router with a Medium preference 🎀

Bestie, the Route Information Option is the star here, so make sure the isolated prefix is in there 🫶

6. Security Considerations ✨

Okay, security time, and I'm taking this one seriously 🔥 A malicious node could send Router Advertisement messages that specify a High Default Router Preference or carry specific routes, and the effect would be pulling traffic away from legitimate routers 😈 But honestly, a malicious node could easily get that same effect in other ways too 💀

For example, it could fabricate Router Advertisement messages with a zero Router Lifetime from the other routers, which makes hosts stop using those routes 😭 If it advertises a specific prefix, the attack can happen in a sneakier, less noticeable way 🙈 Still, this attack has no significant incremental impact on Internet infrastructure security 🧚

A malicious node could also put an infinite lifetime in a Route Information Option so the route lingers forever ♾️ A similar attack already exists with Prefix Information Options in RFC 2461, where a malicious node makes a prefix look on-link indefinitely, which causes a lack of connectivity if it isn't actually on-link 😱 By contrast, an infinite lifetime in a Route Information Option just makes router reachability probing keep going indefinitely, and it does not cause a lack of connectivity 🌈

Similarly, a malicious node could try to overload hosts with a huge number of routes in Route Information Options, or with very frequent Route Advertisements 🍓 Again, this same attack already exists with Prefix Information Options 💅

[RFC3756] gives more details on the trust models, and there's work in progress in the SEND WG on securing router discovery messages that will address these problems 🫶✨

7. IANA Considerations

Section 2.3 defines a new Neighbor Discovery [RFC2461] option, the Route Information Option 🎀 It's been assigned the value 24 within the numbering space for IPv6 Neighbor Discovery Option Formats 🔥

8. Acknowledgements

The authors want to give a huge shout-out to Balash Akbari, Steve Deering, Robert Elz, Tony Hain, Bob Hinden, Christian Huitema, JINMEI Tatuya, Erik Nordmark, Pekka Savola, Kresimir Segaric, and Brian Zill 💖👑 The packet diagrams are derived from Neighbor Discovery [RFC2461] 🦋

9. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
          Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
          Discovery for IP Version 6 (IPv6)", RFC 2461, December
          1998.

[RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
          in IPv6", RFC 3775, June 2004.

10. Informative References

[RFC2080] Malkin, G. and R. Minnear, "RIPng for IPv6", RFC 2080,
          January 1997.

[RFC2893] Gilligan, R. and E. Nordmark, "Transition Mechanisms for
          IPv6 Hosts and Routers", RFC 2893, August 2000.

[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains via
          IPv4 Clouds", RFC 3056, February 2001.

[RFC3756] Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor
          Discovery (ND) Trust Models and Threats", RFC 3756, May
          2004.

Authors' Addresses

Richard Draves
Microsoft Research
One Microsoft Way
Redmond, WA 98052

Phone: +1 425 706 2268
EMail: richdr@microsoft.com


Dave Thaler
Microsoft
One Microsoft Way
Redmond, WA 98052

Phone: +1 425 703 8835
EMail: dthaler@microsoft.com

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