I install debian stretch to my old IBM System x3650 yesterday. This old server has a NetXtreme II BCM5708 Gigabit Ethernet from Broadcom that need a load non free firmware. And my install attempt crash with this error:

[  82.956477] bnx2 0000:03:00.0: firmware: failed to load bnx2/bnx2-mips-06-6.2.3.fw (-2)
[  82.956481] bnx2 0000:03:00.0: Direct firmware load for bnx2/bnx2-mips-06-6.2.3.fw failed with error -2

So, how load this non free firmware during instalation and make a NIC ethernet card to UP ?

Firmware during the installation

In some cases the installer detects the need for non-free firmware and prompts the user to make the firmware available to the installer to complete the installation. This can happen, for example, with wireless network cards which often require non-free firmware to function.

A suggestion, especially when installing on unfamiliar hardware, is to download the firmware archive for your platform and unpack it into a directory named firmware in the root of a removable storage device (USB/CD drive). When the installer starts, it will automatically find the firmware files in the directory on the removable storage and, if needed, install the firmware for your hardware. You can find firmware downloads for your Debian version here: debian firmware .

Another sources for debian stretch firmware is at:

https://packages.debian.org/search?keywords=firmware

Edit CD/DVD install image for debian stretch

First, download your needed firmware. For my purposes is missing firmware at this page: https://packages.debian.org/stretch/firmware-bnx2. Download CD/DVD iso image from https://www.debian.org and copy this image with all firmware files to one directory.

Install to your desktop pc isomaster program:

]$ apt-get install isomaster

After install start isomaster, open your downloaded debian stretch iso image like debian-9.4.0-amd64-xfce-CD-1.iso file. Go to firmware directory and add all firmwares.

isomaster debian stretch iso edited

When you add your firmware to iso image burn to CD or DVD and install like usually.

After edit install image

After install you get this OK message from dmesg:

[    7.504328] bnx2 0000:03:00.0: firmware: direct-loading firmware bnx2/bnx2-mips-06-6.2.3.fw
[    7.507854] bnx2 0000:03:00.0: firmware: direct-loading firmware bnx2/bnx2-rv2p-06-6.0.15.fw
[    7.621110] bnx2 0000:03:00.0 enp3s0: using MSI
[    7.621183] IPv6: ADDRCONF(NETDEV_UP): enp3s0: link is not ready
[   10.873363] bnx2 0000:03:00.0 enp3s0: NIC Copper Link is Up, 1000 Mbps full duplex
[   10.873452] IPv6: ADDRCONF(NETDEV_CHANGE): enp3s0: link becomes ready