Middle Boxes Lixia Zhang UCLA Computer Science Dept Sprint Research Symposium March 8-9, 2000

3/8/002 What are middle boxes?

3/8/003 What are the end boxes? client server Back 20 years… What's on the net - servers/clients (e.g. telnet, ftp, ) - later: peers (e.g. VT) data delivery between the end boxes directly Internet IP delivery

3/8/004 The Role of IP Delivery IP delivers packets from end to end the ends are defined by the communicating application process the ends are indicated by the source and destination addresses in the IP header client server routers

3/8/005 What are middle boxes? data is no longer delivered between the two end boxes by direct IP path The first middleman: server middle box client server sender recipient always connected In the early days:

3/8/006 What are middle boxes? data is no longer delivered between the two end boxes by direct IP path The first middleman: server middle box client server sender recipient server always connected Intermittent connectivity As time went:

3/8/007 Every coin has two sides Gain from having such a middlebox: solved the asynchrony problem between the two ends of delivery Loss for having a box in the middle: –more parts in the system to mingle with –more points of potential failures sender recipient server

3/8/008 sender recipient server The position of server in the IP architecture An application level box – sender talks to server explicitly – recipient fetches from the server explicitly in another word, not a "transparent" box

3/8/009 What we've seen in last couple of years A lot more middle boxes –Web proxies –"transparent" Web caches –portals Web server client Packet hijacking! ("for your benefit") Web proxy

3/8/0010 And more middleboxes yet to come e.g. Proxy servers to facilitate mobile wireless devices and mobile users in handling –intermittent connectivity –location tracking –link QOS constraint –session migration

3/8/0011 What we've seen Growing up of the Internet, of course need for scalable data dissemination –large number of clients requesting same data –requests coming in asynchronously need for information discovery/sorting need for authentication/security and all other kinds of services

3/8/0012 Challenges from growth large number of clients, large number of mobile users, large number of servers too How to do it right? So far pretty much "one hundred flowers blooming" –Web proxies –abuse DNS for load balancing –"transparent" caching –"layer switching", 3 < < 10?

3/8/0013 What's coming Big part of the society moving online what makes up the society & business market: mostly middlemen –largely missing on the Internet the reason that the Internet, by and large, does not look user-friendly to most people Prediction –a lot more middle boxes –IP packet delivery infrastructure fades into background—ubiquitous IP connectivity everywhere

3/8/0014 User programs application protocols transport protocols IP various networks WWW phone... SMTP HTTP RTP... TCP UDP… IP ethernet PPP… CSMA async sonet... copper fiber radio... For now: nowhere, or everywhere haven't you heard the hot buzzword "transparency"? "Internet architecture" ? Where in the architecture do those new middle boxes belong to? Does that raise a concern? YES

3/8/0015 Concerns about transparent middleboxes "transparent" middleboxes considered harmful –packet hijacking versus system manageability –Users: being in control versus being controlled Sticking to the layered protocol architecture considered necessary

3/8/0016 Where middle boxes belong to in the Internet architecture should be application level boxes being visible to end users Middleboxes and end-to-end principle: consider middle boxes as one "end" of "end-to-end" –e.g. the mail server in delivery

3/8/0017 Middleboxes: gains Keep the waist of the hour-glass thin –manageable, scalable, robust connectivity help the Internet scale with growing applications & client population Provide real services, all kinds of them –personalized portals –heterogeneity –building new services from existing applications

3/8/0018 Some potential losses (or things we need to pay attention) Dependency on those middleboxes –increased complexity –increased vulnerability "directory-enabled network": the network is gone when directory crashes, even if all switches are up –a robust, self-configured, self-organizing middlebox infrastructure can lead to higher availability and more robustness more complex security and trust model impact on data integrity

3/8/0019 Summary Finally the Internet is growing up! –Past efforts mostly on packet delivery –Now people start making money out of this packet delivery service middle boxes are a must Warning: pay attention to architecture Right way out: building application level infrastructures on top of the packet delivery infrastructure