Ok, this is a weird one. I noticed that a vpdn configuration that I have used since 12.2 was not doing what I expected in 12.4(15)T. In particular, udp checksums were not on even though the vpdn group specified "l2tp ip udp checksum". As far as I can tell, this configuration command is now completely ignored in the vpdn group itself although it does work if applied to the unnamed vpdn template. This is true even if the vpdn group specifies "no source vpdn-template". Were it not for the latter I would think they just got the sense of "default" reversed but clearly something more is going on. Perhaps the unnamed vpdn template has become the system default template as well? (Explicit named vpdn templates also allow checksums to be enabled.)
There has always been an issue with the hierarchy of vpdn configuration commands as it clashes with the idea of not including default values in the configuration. Parameters specified in a vpdn group are supposed to take precedence over those in any linked template but there is no way to specify a parameter that would be the default were it not for the template. Possibly someone is trying to clean this up and is fiddling with the code?
Dan Lanciani ddl@danlan.*com