On Cisco ADSL routers, there is a wide choice of modem firmware releases available, as well as IOS releases; each IOS release comes with its built-in modem firmware, but you can override it with a custom (and possibly more recent/stable/performant) one.

For example, this is the modem firmware download page for a Cisco 887VA router: https://software.cisco.com/download/release.html?mdfid=283122091&softwareid=282821780.

As usual with Cisco, the version numbering is quite convoluted; the release notes are also not clear about how, when and why a firmware should be considered better than another one.

This router is currently running IOS release 15.5.3M (the latest available), which seems to include the modem firmware A2pv6C035j (output from show controllers vdsl 0):

Firmware        Source          File Name
--------        ------          ----------
VDSL            embedded        VDSL_LINUX_DEV_01212008

Modem FW  Version:      130205_1433-4.02L.03.A2pv6C035j.d23j
Modem PHY Version:      A2pv6C035j.d23j

The latest available firmware releases are:

  • B2pvC038h3_j
  • A2pv6C039m
  • VAa38qb38r124j
  • VAa39db38h324h

All of them have been released in 2014, while the IOS release is from 2015, thus it should include the latest modem firmware; however, the same page lists the firmware release embedded in this IOS as being from 2012 (!).

I really can't make any sense of all those firmware releases and their differences. Based on the version name, at least A2pv6C039m seems to be a direct successor of A2pv6C035j; I don't know about the other ones; it also seems to be the very latest one released, apart from B2pvC038h3_j, which however seems to be specifically targeted to Annex J lines and would thus be probably unfit for Annex A lines like mine.

Which firmware should I use? The built-in one or one of those available for download? And, in this case, which one? And why?

Bonus points: can someone please explain what do their names mean and what their differences are?

1 Answer 1


If you use a 887VA you will want to use A2pv6C039h. You can see which routers are supported by checking the release notes of the firmwares. Some only work on a subset of the 88x series. Others are only for special networks e.g. have an option to use the "modem" command to specify abnormal DSL settings.

As for the firmware embbeded into IOS: Most of the times its rather old (as you said) and if you are experiencing trouble try to upgrade the DSL firmware. Sometimes newer firmware also gives you new features (e.g. vectoring for VDSL). For Cisco it makes sense to use a old but stable VDSL firmware inside of IOS. If you want bleeding edge features, then use a seperate firmware.

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