This is a solution to a problem we have had. Since I haven't found
any other references to it on the web but I know from IBM that other
people have had the same problem, here is the solution we have found.

Symptoms :
During a network boot (NIM on its own or via PSSP), it all looks OK
but the BOOTP and tftp packets go very slowly. Sometimes bootp times
out. Normally it gets to tftp but receives only 100 packets every
10-30 seconds (should be about 300 packets a second). Eventually it
falls over.

There are a few things we ruled out, which could also be the problem
- make sure all adapter and switch ports set to the same speed (e.g.
100Mb full duplex, 10Mb half duplex)
- boot up the NIM client and try to tftp the file (from /tftpboot on
the NIM master) manually. It came across at normal speed when we
tried this.
- try booting from a different SPOT just make sure it isn't some
problem with the spot file itself coming over.
- Upgrade NIM client firmware to latest level and apply latest
maintenance level to NIM master.

Solution :
If none of that fixes the problem, check the ethernet adapter you are
booting from. If it is a f/c4962 10/100 PCI Ethernet Adapter II
(1410ff01) then check the microcode.

lscfg -vl entx --> ROM level (alterable).
If the ROM level is SCU001 you need to upgrade to fix this bug.
Download the latest microcode from
http://techsupport.services.ibm.com/...d.html#adapter
(currently SCU015) and apply it.

There were three gotchas we saw with the microcode update
1. The intructions say that the update takes the adapters offline for
you. When we tried, it did this sometimes but not others. Where it
didn't, the microcode update returned an error. Manually taking the
adapter offline (ifconfig down; ifconfig detach) and re-running fixed
this.
2. Only the most recent version of invscout picks up this adapter as
one that has upgradeable microcode at all, never mind that its
downlevel. If you are relying on invscout, it probably missed this
one.
3. Since the upgrade gets applied to all adapters and takes them down
(when it works), remember to be logged on either via the
console/serial link or via another sort of adapter (not a f/c4962) so
you don't lose your connection during the upgrade.

Iain.