Cisco IOS Release Naming

Letter Definitions for Cisco IOS Release Trains

The first character assigned to the release is based on the technology specific to that release. These are technology characters utilized in Cisco's IOS Release deployment.


A = Aggregation/Access Server/Dial technology


B = Broadband

C = Core routers (11.1CA, 11.1CT, 11.1CC)

D = xDSL technology

E = Enterprise feature set

F = Feature Specific enhancements (11.2F)

G = Gigabit Switch Routers (GSR)

H = SDH/SONET technology (11.3HA)

J = Wireless Networking technology (Aironet)

M = Mobile (Restricted to Mobile Wireless BU usage and further reserved for Mainline)

N = Voice, Multimedia, Conference (11.3NA)

P = Platform features (11.2P)

R = Reserved for ROMMON reference

S = Service Provider

T = Reserved for Consolidated Technology Train

W = LAN Switching/Layer 2 routing

X = A short lived, one-time release (12.0XA)

Y = A short-lived, one-time release (when Xs are exhausted)

Z = A short-lived, one-time release (reserved if Ys are exhausted