Minimum TTLs This note explores the use of short TTL's for failover (short TTLs have no role to play in load-balancing) and seeks to answer the apparently simple question - what is the lowest sensible TTL? The related, and far more important question, 'Is a short TTL the best failover strategy?' Is dealt with in ( hint: multiple RRs are a faster and more reliable strategy). In answering the TTL question three assumptions are made: • Failover is designed to provide an alternative IP address in the event of a server/service or access route failure. That is, the Authoritative DNS will replace the IP address in the A RR pointing to the service when local equipment detects a failure.

The failover method could be called, for want of any better terminolgy, single-service-ip-with-dynamic replacement. • The service for which failover is required is TCP based, for example, HTTP, HTTPS or FTP and is initiated typically from a web browser. TCP error recovery methods are defined within the protocol whereas UDP error recovery methods are application based and therefore subject to multiple variables. • The majority of clients accessing the services are based on Microsoft's Windows series of OSes (simple fact of life - over 90% are). There is no doubt that local equipment can efficiently and effectively monitor the health and availabilty of important services and rapidly replace failing services by switching in a backup/hot standby and changing the IP address in a DNS A RR. However, what such local equipment cannot do is to monitor every communication path from every user.

If a communication link is out for an temporary period then significant numbers of users may be affected while the local equipment continues to see a perfectly functioning service. Multiple IPs (with geographic separation) will solve this problem.

The author of this note considers low - sub one minute - TTLs to be inherently evil for 3 reasons: • Load: They place a huge - and unnecessary - load on domain name servers and the DNS infrastructure - specifically caching name servers in service provider locations. • Reliability: The reliability level of the DNS becomes the limiting factor in service availability. • Cache Poisoning: Since each DNS access offers the possibility of cache poisoning it seems reasonable to limit that possibility as much as possible. Certain well known attacks such as documented in which represent modest risk at TTLs of 3,600+ seconds (i hour +) suddenly become serious with a TTL of, say, 5 seconds such that there is a 10% possibility of poisoning after 2 minutes and 90% after 40 minutes. Not comforting numbers. Note: During the course of running some experiments, for this and another article, some bizarre artifacts of a DSL modem and/or DNS proxies were observed. The net result was that invalid DNS results were returned when similar DNS requests were issued within 15 minutes.

Another reason to keep TTLs high? The Process of a Name Lookup Figure 1 shows why TTLs of less that 30 minutes have absolutely no effect on failover performance for current site users when using MSIE but shorter TTLs will have an impact on new site visitors.

Nominally Firefox users would reread the DNS every 60 seconds but since it takes approximately 3 minutes for the browser to finally give up and notify the user of a failure the minimum sensible TTL for Firefox users would be 3 minutes. To explain this reasoning it is necessary to understand the process by which IP addresses eventually end up in a browser and which is illustrated in Figure 1 below. Figure 1 Caching effect in browsers The crux of the problem is caching - not in the DNS servers but in the browser. Figure 1 shows the process used to obtain an IP address by a browser.

Minimum TTLs. This note explores the use of short TTL's for failover (short TTLs have no role to play in load-balancing) and seeks to answer the apparently simple. As well as new machinery, Kluge markets and sells used equipment in the following formats: Remanufactured, Certified or As-is condition. Kluge Remanufactured EHD 14 x 22 with Adjustable Impression. Know the serial number of the machine, call the original manufacturer for the history of the equipment.

The browser requests the IP address using a POSIX standard resolver library function (1) - either gethostbyname() or the newer version getaddrinfo() or in the MSIE case a non-POSIX equivalent call is used. The local resolver (2) initiates a standard DNS query to its locally defined DNS (3) - typically located at a service provider - which, being a recursive DNS, will initiate one or more DNS queries to the DNS infrastructure finally resulting in a query to the domain owners authoritative name servers (4). The responses to DNS queries contain the full DNS RR(s) including the TTL.

Thus, the response paths 4->3 and 3->2 will contain the TTL data, say, 5 seconds. The library function (path 2->1) response is not specified to contain TTL data (even Microsoft's non-POSIX functions do not return TTLs values).

The TTL information at this point is effectively lost. The browser - in order to speed up performance - maintains a cache of results which in the abscence of any other information is timed out after 30 minutes in the case of MS Explorer and 1 minute in the case of the Mozilla family (configurable in both cases). Thus, the IP address will not be replaced, irrespective of the TTL value, for 1 to 30 minutes for existing site visitors. Finally, we need to consider the time the browser and TCP/IP stack between them take to decide when a site is unreachable. In the case of MSIE this is around 2 minutes and in the case of Firefox around 3 minutes (the difference is entirely to do with retry strategies adopted by the respective browsers). The problem is entirely one of mismatched objectives. The browsers wish to optimise performance by mimimising external accesses; whereas the resolver library system calls (whether POSIX or MS) wished to mimimise complexity by reducing the amount of information returned.

However, by not returning the TTL from the DNS records the system calls eliminated the only basis on which a sensible DNS cache strategy can be based. Instead we have a kluge. Update: The original tests were done in 2006 with MSIE 6. MSIE 7, 8 and 9 use the same settings and strategy for DNS cache timeout.

MSIE 10 and 11 strategy and DNS caching defaults are currently unknown. Note: The increasingly common DSL/Cable modem (5) almost always contains a DNS Proxy whose functionality varies from the relatively benign (transparent) to the downright intrusive (preventing queries for a period - in some case 15+ minutes - by serving from a cache irrespective of the actual TTL value) in order o reduce loaad on the ISPs infrastructure.

Clearly new visitors whose browser has no cache entry will obtain a new IP address using the same process defined above and therefore the short TTL will have the desired effect of providing the up-to-the-second IP address. So the answer to the question 'what is the most sensible minimum TTL?' Depends on whether you think it more likely that the service will break during a visit - in which case 180 seconds (3 minutes - if all visitors are Firefox) or 1800 seconds (30 minutes - if all vistors are MSIE) seem reasonable values - or on the initial visit - in which case set the TTL to some very low value and spend serious bucks on DNS hardware. Alternatively you could consider other failover strategies - such as multiple RRs which are. Problems, comments, suggestions, corrections (including broken links) or something to add?

Please take the time from a busy life to 'mail us' (at top of screen), the webmaster (below). You will have a warm inner glow for the rest of the day.

Contents • • • • • • • • • • • • • • History [ ] Origins [ ] The company arose from the ashes of the, the world's first commercial. DuMont had been in economic trouble throughout its existence, and seriously undermined when accepted a buyout offer from in 1953. The ABC-UPT deal gave ABC the resources to operate a national television service along the lines of and.

DuMont officials quickly realized the ABC-UPT deal put their network on life support, and agreed in principle to merge with ABC. However, it was forced to back out of the deal when minority owner raised antitrust concerns. UPT had only spun off from Paramount four years earlier, and there were still doubts about whether the two companies were really separate. By 1955, DuMont realized it could not compete against the other three networks and decided to wind down its operations. Soon after DuMont formally shut down network service in 1956, the parent firm spun off the network's two remaining, WABD in New York City and in Washington, D.C., to shareholders as the DuMont Broadcasting Corporation. The company's headquarters were co-located with WABD in the former DuMont Tele-Centre (which was later renamed the Metromedia Telecenter) in New York.

In 1957, DuMont Broadcasting purchased two New York area radio stations, WNEW (now ) and WHFI (later and WWFS), and later that year changed its name to the Metropolitan Broadcasting Corporation to distance itself from its former parent company. The following year, Paramount sold its shares in Metropolitan Broadcasting to Washington-based investor, enough to give Kluge controlling interest. Kluge installed himself as chairman, and later increased his holdings to 75 percent. WABD's were later changed to WNEW-TV to match its new radio sisters.

Expansion [ ]. 1970s logo for WTCN-TV (now ) in, which included the corporate logo for Metromedia; this logo was also used by in Los Angeles Metromedia's first acquisitions included - in (in 1958); the Foster & Kleiser outdoor advertising firm (in 1959); and in, WIP-- in, WTVH-TV (now ) in, and WTVP television (now ) in (all in 1960). In 1961 Metropolitan purchased KMBC-- in. Later that year the company's name was changed to Metromedia; the Metropolitan Broadcasting name was retained for its broadcasting division until 1967. In separate 1963 deals the company expanded into, buying first and later and the original KLAC-FM (now ). The company would later engineer a swap of FM facilities; the second KLAC-FM (later and now ) was established in 1965.

Metromedia also entered the realm of live entertainment by purchasing the (in 1963) and the (in 1967). Later in the decade Metromedia opened a television production center in Los Angeles, known as, which served as the studio facility for numerous network programs. Metromedia also owned a TV production and distribution company called Metromedia Producers Corporation (MPC), established in 1968 from. MPC produced and syndicated various programs and TV movies, most notably the and the 1972-86 version of. Metromedia spent the 1970s and the first half of the 1980s increasing its television and radio station portfolio, and continued to expand its syndication business. Metromedia entered the in 1969 with the launch of the Metromedia Records label, whose biggest-selling artist was. The label was also notable as having issued the first two studio albums of, (1971) and (1972).

The label was closed as of 1974. Allen's Tenterfield Saddler, the title song of which has become an, was acquired and reissued by in 1978. In 1976, similar to the more successful of syndicated stations launched two years later, Metromedia teamed up with for a proposed linking of independent TV stations termed MetroNet. The proposed programming would consist of several Sunday night family dramas, on weeknights a half-hour serial and a gothic series similar to, and on Saturdays a variety program hosted.

The plans for MetroNet failed when advertisers balked at Metromedia's advertising rate, which was only slightly lower than the Big Three's and low national coverage, leaving for another similar operation,. In 1982, Metromedia made its biggest broadcasting purchase when it acquired in for $220 million, which at the time was the largest amount ever spent on a single television station property. Two years later, John Kluge bought out Metromedia's shareholders and took the company private. 1985-86 divestitures [ ] On May 4, 1985, Kluge announced the sale of Metromedia's television stations, and Metromedia Producers Corp., to (owned by Australian newspaper publisher ) and (owned jointly by Murdoch and ) for $3.5 billion.

With the exception of WCVB-TV (which was subsequently sold to the ), all of the former Metromedia stations formed the nucleus of the, while MPC was folded into. The transactions became official on March 6, 1986. Kluge also sold Metromedia's outdoor advertising firm, the Harlem Globetrotters, and the Ice Capades in that same year, and spun off the radio stations into a separate company (which ironically took on the Metropolitan Broadcasting name) before they were sold to various other owners by the early 1990s. Continued usage of the Metromedia name [ ] The Metromedia name has lived on in other projects by Kluge such as the, though the ventures have been largely unrelated to television. The callsign of radio station in first stood for 'MetroMedia Radio'. Similarly, radio station in first stood for 'MetroMedia Stereo'.

In early 2011, former Metromedia Radio trademarks were registered with the US Department of Commerce by a midwestern businessman, combined with a large collection of the WNEW 1130 AM archive library: old shows, concerts and jingle packs, a new 'Metromedia Radio' started broadcasting over the internet. In 2012, working with Dick Carr, former executive of legacy Metromedia and WNEW radio on air talent Bill Quinn, the new Metromedia Radio expanded into production of radio content for syndication across North American terrestrial radio stations. In 2014 WBGO radio talent Rich Keith partnered with Metromedia Radio in the production and syndication of 'Pure Jazz', other shows syndicated by Metromedia Radio include: Martini Mix with Mike Martin, M Squad with Marty Wilson (formerly of WNEW) and An Evening At The Buddies Lounge. Metromedia Radio is also the exclusive broadcaster of the critically acclaimed show The Sinatra Songbook, hosted by Mark Sudock. Metromedia Radio's broadcast stream can be found on Live365, Tunein, Streema and Streame.co. Based on the common link to Metromedia, television historian claims that Fox is a direct descendant, if not a revival, of DuMont.

Indeed, the former WNEW-TV, now Fox flagship, is still headquartered in the former Metromedia (and before that, DuMont) Telecenter, now known as the Fox Television Center. An east entrance of the Fox Television Center in fact still contains an entrance with door handles containing the final Metromedia logo.

Legal battles [ ] In retaliation for a lawsuit brought by, who sought the rights to his children's television program Winchell-Mahoney Time, which was produced at KTTV in Los Angeles during the middle 1960s, it is believed that KTTV management the program's video tapes. In 1989 Winchell was awarded nearly $18 million as compensation for Metromedia's capricious behavior. In 1983,, a former evening news co-anchor at KMBC-TV in Kansas City, sued Metromedia on claims of fraud and. After spending eight months at KMBC-TV in 1981, she was demoted to reporting assignment after a study claimed Craft was 'too old, too unattractive and not deferential to men' in the eyes of viewers. Craft declined the reassignment and subsequently resigned from the station.

Craft initially won her case, though she lost on appeal at the. Ownership of Orion Pictures [ ] On May 22, 1986, Metromedia acquired a 6.5% stake in; a movie and television studio. By December, the stake in Orion's ownership was increased to 9.3% to 12.6% and on April 12, 1988, to 44.1% On May 20, 1988, Metromedia acquired 's share for $78 million, holding a majority stake in Orion Pictures worth nearly 67%. In 1996, Metromedia acquired and.

On April 11, 1997, Metromedia sold Orion/Goldwyn and MPCA to for $573 million and was closed on July 10 of the same year. In 1998, MPCA broke apart from MGM becoming independent again. Typeface [ ] Beginning in 1967, Metromedia's television stations began utilizing a sans-serif font for their on-air logo. The typeface was a proprietary font called Metromedia Television Alphabet, which was as distinctive as the typeface employed by for its TV and radio stations beginning in 1963. Metromedia Television Alphabet was used for the channel numbers of its television stations until 1977, when another typeface modeled slightly after the family was introduced. Former Metromedia stations [ ] Stations are listed alphabetically by state and.

Space Jam Soundtrack Download. Notes: • Two boldface asterisks appearing following a station's call letters ( **) indicate a station that was built and signed-on by Metromedia or its predecessor companies. • This list does not include WDTV (now ) in or in Kansas City.

Although DuMont owned the two stations at some point, Metromedia never owned either of these two stations. This list is; you can help. • (1969) • (1958-1961) • • • • (1975-1980) (co-produced with ) • (1950-1952, 1956-1959) • (1973-1974) (co-produced with and Writer First Productions) • (distributor, 1985–1986) • Expedition Danger • • (1974) (co-produced with Stonehenge Productions) • • (co-produced with ) • • (1973) • (co-produced with Productions) • and the World of Animal Behavior • (original version - distributor, 1974) • (1978-1982) • Little Gloria: Happy at Last (1982; mini-series) • (distributor) • (distributor/co-producer, 1972–1983) • (distributor) • (distributor) • Specials (1964–71) • (U.S. Distributor) • The New Show (1976-1977) • (1981–82; distributor) • (1971–72) (co-produced with Films) • (1953-1957) • (1969–1970) • • (production company, 1985–1986) • (syndicated by then Trifecta Entertainment and Media) • (production company, 1983–1986) • • • • (1972) • • (distributor) • (distributor) • (1980-1987) (co-produced with D.L. Taffner Productions) • (distributor, 1966–1978) (co-produced with ) • The Undersea World of • The Untamed World • Vauldeville • (1978-1981) (distributor) • Wild Times (1980; mini-series) • -Mahoney Time (1965-1968) • (1955-1977, 1980-1983). • ^ Rights now owned. • ^ MPC was the international distributor for these programs.

Distribution was later transferred to, following Murdoch's acquisition of MPC. These programs ane now distributed worldwide. In the United States, and its predecessor, Columbia Pictures Television, was always the distributor of syndicated repeats of these programs. • Currently owned. • Currently owned by Tanslin Media. • Rights now owned.

• ^ Currently distributed. • Currently distributed by on behalf of The Griffin Group. • ^ Currently distributed by the.

• Rights now owned. • Later distributed by and. • Rights now owned by Paul Winchell's family. References [ ]. Retrieved on 2013-08-16.

•; Wolf, Marvin J. Beating the Odds. New York: Macmillan. Archived from on 2006-12-31. Retrieved 2006-12-31.

• Kamal Masood Mp3 Songs Free Download here. 'DuMont network to quit in telecasting 'spin-off.' ', August 15, 1955, pg. [ ] • 'DuMont completes spin-off, separates broadcasting, labs.'

' Broadcasting - Telecasting, December 5, 1955, pg. [ ] • 'DuMont pays $7.5 million for WNEW.' Broadcasting, March 25, 1957, pp. [ ] [ ] • [ ] • 'For the Record.' Broadcasting - Telecasting, January 6, 1958, p. [ ] • 'DuMont revenue grows, name change approved.'

Broadcasting, May 19, 1958, pg. [ ] • 'Kluge buying Paramount's 21% of Metropolitan Broadcasting.' Broadcasting, December 1, 1958, pg. [ ] • [ ] • [ ] • Spielvogel, Carl. 'Advertising: an acquisition set.' • '3 blessings with 2 rebukes.' Broadcasting, January 4, 1960, pg.

[ ] • [ ] [ ] • 'Metropolitan buying KMBC.' Broadcasting, December 26, 1960, pp. [ ] [ ] • 'It's Metromedia.' Broadcasting - Telecasting, April 3, 1961, pg. [ ] • ^ 'Metromedia gets its TV team in uniform.'

Broadcasting, March 25, 1968, pp. [ ] [ ] • 'KTTV to Metromedia for $10 million plus.'

Broadcasting, January 14, 1963, pg. [ ] • 'Metromedia adds KLAC in $4.5 million deal.' Broadcasting, March 18, 1963, pp. [ ] [ ] • 'Changing hands.'

Broadcasting, March 22, 1965, pp. 110-111: Metromedia acquires KRHM (94.7 FM) and sells KLAC-FM (102.7 FM); the FCC allows both facilities to exchange call letters. [ ] [ ] • 'Ice Capades Acquired By Metromedia, Inc.'

The New York Times, May 14, 1963. • Gent, George. 'Metromedia buys Globetrotters; TV chain will add team to Ice Capades operation.' The New York Times, May 24, 1967. •; www.allmusic.com. •; www5d.biglobe.ne.jp.

• Nadel, Gerry (1977-05-30).. New York Magazine. New York: 34–35. Retrieved 2009-10-04. • Schwartz, Tony. 'Metromedia seeks TV station.'

The New York Times, July 23, 1981. • Cuff, Daniel F. 'Business people; Metromedia's founder begins new challenge.' The New York Times, Dec. • Cole, Robert J. 'Murdoch to buy & TV stations; cost $2 billion.'

The New York Times, May 7, 1985. The 10 O'Clock News. New York, NY.

00:00 minutes in. Retrieved 5 November 2017.

• Stevenson, Richard W. 'Metromedia ad business sale'. The New York Times, Jan. • Fabrikant, Geraldine. 'Metromedia set to sell Globetrotters, ice show.' The New York Times, Mar. • 'Metromedia, Katz radio groups sold in LBO's.'

Broadcasting, March 31, 1986, pp. [ ] [ ] • [ ] •. The Retrologist. 12 April 2012. Retrieved 19 July 2015. • [ ] • • 'Newsroom issue goes to court.'

Broadcasting, August 1, 1983, pp. [ ] [ ] • 'Craft decision leaves questions.' Broadcasting, August 15, 1983, pp. [ ] [ ] [ ] • [ ] • 'Christine Craft wins two, loses big one.'

Broadcasting, March 10, 1986, pp. [ ] [ ] •, chicagotribune.com •, newyorktimes.com • Bates, James.. April 29, 1997. • 'Years of Hits, Misses Comes to Close.' July 10, 1997; Bates, James.

'MGM Lays Off 85 in Metromedia Film, TV Units.' Los Angeles Times. July 11, 1997. • '$9.65 million sale of KMBC.'

Broadcasting, July 31, 1961, pp. [ ] [ ] External links [ ] • at the Encyclopedia of Television • on (subscription required) • on (subscription required) • on (subscription required) ( Note - although three separate companies are listed on the IMDb, it should be understood that Metromedia Producers Corporation, Metromedia Productions and Metromedia Television are all different names given for the same production company.) •.