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Did you notice 15.1T is released?

Unveiling of the Cisco IOS release 15.1(1)T was the extreme opposite of the CRS-3 and Catalyst 3750-X splashes; the next release of one of the foundations of Cisco’s core business deserved a modest two-paragraph mention in the What's New in Cisco Product Documentation page.

If you’re a voice guru, you’ll probably enjoy the list of 20+ voice-related new features, including the all-important Enhanced Music on Hold. For the rest of us, here’s what I found particularly interesting:

And, finally ... Tcl supports UDP sockets and VRF-based sockets. We’ll have so much fun with this feature; for example, we’ll be able to wake a host from a router or connect to an external server residing in a VRF.

Oh, BTW, if you wanted to save money and test this release on your Dynamips-enabled 7200 clone, you’re out of luck; 15.1T runs only ISR and newer hardware.

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  1. "Cisco 7200 series and Cisco 7301 routers will continue to be supported in Cisco IOS 15.x(x)M releases. Only the Cisco IOS 15.x(x)T releases will not support the Cisco 7200 series and Cisco 7301 routers. "

    Well I guess it's time to see if 2800 emulation is doable.

  2. Ivan Pepelnjak02 April, 2010 11:34

    If I remember correctly, many I/O components are made by a manufacturer that gives you the specs only under an NDA.

  3. Saw this a couple of days ago. But what happened to 15.0T?

  4. Ivan Pepelnjak02 April, 2010 16:55

    I have to admit, I'm totally confused by their new numbering schemes. There's a product bulleting "explaining" them, but it only made me more confused.

  5. Exactly. So the next mainline rebuild is 15.1M? That was fast...

  6. When I was at the ISRg2 launch event in boston they explained it and it made complete sense, but since the presenter never followed up with the slides like he said I completely forget the procedures.

    it is something to the effect of the 15.0T becomes 15.1M after testing completes, or something like that

  7. yesterday a new CCIE track was launched without much ado : the Numbering track.

    CCIE Numbering experts will have the outstanding ability to find if a bug fixed in release A is fixed in release B. They will understand why new features are inadvertently introduced in mainline trains and why developers forget to commit fixes in the branches where the bugs were discovered. They will master the double numbering of IOS-XE and the sudden change from 12.2XN to 15.0S.

  8. No, I will not go for the CCIE Numbering track, seems to complicated.

  9. @kcuorbax see if cisco had a sense of humor they definitely should have done that

  10. Would be fun going to Brussel one more time. Requirement: implement feature X not used by anyone. Find and load correct IOS image.

  11. Would be fun going to Brussel one more time. Requirement: implement feature X not used by anyone. Find and load correct IOS image.

    But no, probably just another 1400$ beer at the airport

  12. The Delta between the 15T and the next 15M release is much shorter than what it used to be. Once the next M version becomes available you can run the same feature on the 7200 as well.

  13. The Delta between the 15T and the next 15M release is much shorter than what it used to be. Once the next M version becomes available you can run the same feature on the 7200 as well.

  14. So maybe the 3825/3845 would be a better choice: they're based on a BCM1250 whose specs are available.

  15. Does 15.1T IOS support Zone Based Firewall for IPv6?

  16. It's quite simple. The 15.0(1)M gets released. Now, all development will continue in releases that will be numbered from 15.1(1)T, until fixed amount of time passes - currently 20 months, and then new mainline release will be available - like for example 15.2(1)M. However, there's no "mainline" anymore, as there's one software track.

    However, between 20 months cycle, there will be rebuilds of software already available, and we already seen that - there's 15.0(2)M as a rebuild of 15.0(1)M and so on.

  17. As it is apparent from release notes, not yet.

  18. Ivan Pepelnjak10 April, 2010 18:46

    Thanks for the explanation. Once we get used to it and manage to forget what we've been living with for the last 15 years, it will start to make sense ;)

  19. Phillip Remaker16 May, 2010 19:42

    @mr0vka : Not exactly correct.

    15.0M is a transition between 12 and 15. "M" indicates a long-lived mainline release. It is the first mainline release, long lived and bugfix only.

    15.1T starts the ".1 epoch" of releases.

    15.1(1)T, (2)T, (3)T will be shorter lived feature releases that each add new features. At some point, the .1 epoch will be feature complete and will graduate to the "M" marker at 15.1(x)M. That M release will be long lived. The value of x is not currently known.

    When (or slightly before) 15.1 becomes a mainline, 15.2(1)T will be the first release of the ".2 epoch" of releases. 15.2(1)T, 15.2(2)T will each be shorter-lived feature-add releases that add features. 15.2T will graduate to "M" status once feature complete after some number of releases.

    Repeat for each epoch, 15.3, 15.4, etc, etc. The "T" changed to "M" when the train is feature complete.

    Logically, M and T are the same software base in this model - the M just serves as a lifecycle marker, like the Ubuntu LTS marker.

    The "S" family of releases run a similar process, but all S releases are called "S" regardless of long lived or short lived status. The planned lifecycle of an S release is determined from the release notes.

    It is critical to note that the 15.1 T and 15.1 S releases will NOT share the exact branch of code the same way that as in the 12.x families. There will be a lot of parts in common, but you cannot assume that 15.1(x)T and 15.1(x)S will be feature-for-feature or bug-for-bug compatible like you could in the 12 releases. is a pretty good reference. (Oh, snap, it doesn't cover the IOS 15 shift...)

    The docs on the web site are lacking in detail. The "graduate to M" idea is not well covered. The new numbering scheme sought to shy away from "low numbers" on a mainline release - "M" now becomes a marker rather than an independent software release train.


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