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:
- Ethernet OAM is finally available on low-end platforms. Now it makes sense to implement end-to-end Carrier Ethernet architectures.
- IP SLA engine was rewritten.
- In a huge engineering effort, mpls mtu command was added to the GRE tunnel interface.
- 15.1T has parser concurrency and locking features from 12.2SRE. They give you a finer locking granularity when multiple engineers concurrently configure the same device.
- Zone-based firewall feature has a few more knobs and show commands.
- The police MQC command finally works on the SVI interfaces.
- DHCP zero-touch deployment allows you to pass pointer to a web-based router configuration to a newly-deployed router in a DHCP option.
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.
Well I guess it's time to see if 2800 emulation is doable.
it is something to the effect of the 15.0T becomes 15.1M after testing completes, or something like that
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.
But no, probably just another 1400$ beer at the airport
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.
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.
http://www.cisco.com/web/about/security/intelligence/ios-ref.html 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.