Juniper ( JNPR) is said to be out of the running for a new networking gear order by AT&T ( T). The apparent winner, according to analysts, is archrival Cisco ( CSCO).

In a research note Tuesday, UBS analyst Nikos Theodosopoulos downgraded Juniper to neutral from buy on concerns that the stock's 38% rise this year has some potential downside. One particular threat to Juniper's gains is the potential loss of a huge customer.

"Our contacts suggest Juniper may have recently lost on a routing opportunity at AT&T vs. Cisco," Theodosopoulos wrote.

Juniper and Cisco are the only two players in the so-called core router market. These are network systems that manage massive flows of Internet traffic for telcos like AT&T, Verizon ( VZ) and nearly every major network operator.

One slightly ominous note in the AT&T story is that Juniper's potential miss comes as AT&T looks to narrow its network equipment vendor list from about 150 suppliers to fewer than 40, according to Telecom Pragmatic analyst Sam Greenholtz.

Juniper declined to comment on the speculation about its status at AT&T.

A Juniper representative pointed to a press release on Monday, which was a re-release of a May 13 AT&T press release. In it, AT&T named Juniper one of its six outstanding suppliers last year. "Commitment to excellence over the past year has earned Juniper recognition as a 2009 AT&T Supplier Award winner," according to the release.

The timing of the re-release was certainly interesting, as was the omission that Cisco was also among the top six suppliers.

Cisco has about 80% of AT&T's routing business with Alcatel-Lucent ( ALU) and Juniper each at 10%, according to another Wall Street analyst, who says Juniper often ends up the loser in contract awards. It would make sense if AT&T were culling its supplier list, but Juniper's role as the Cisco straw man probably isn't in jeopardy, says the analyst.

It doesn't help, however, that Juniper may have lost a "routing opportunity at AT&T." The stock was down 5.5% Tuesday. Then again, there will likely be more opportunities to come at AT&T.

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