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ibm aix 7.1 and LACP

Mind to define the LACP mode with your AIX administrator. Configuring the ports with „channel group # mode active“ did work fine for us. Mode on won’t work if the AIX servers uses mode active. For this also see cisco LACP configuration guidelines under:

Configuring EtherChannels and Link-State Tracking

Here the different modes:

auto—Enables PAgP only if a PAgP device is detected. It places the port into a passive negotiating state, in which the port responds to PAgP packets it receives but does not start PAgP packet negotiation. This keyword is not supported when EtherChannel members are from different switches in the switch stack.

desirable—Unconditionally enables PAgP. It places the port into an active negotiating state, in which the port starts negotiations with other ports by sending PAgP packets. This keyword is not supported when EtherChannel members are from different switches in the switch stack.

on—Forces the port to channel without PAgP or LACP. In the on mode, an EtherChannel exists only when a port group in the on mode is connected to another port group in the on mode.

non-silent—(Optional) If your switch is connected to a partner that is PAgP capable, configure the switch port for nonsilent operation when the port is in the auto or desirable mode. If you do not specify non-silent, silent is assumed. The silent setting is for connections to file servers or packet analyzers. This setting allows PAgP to operate, to attach the port to a channel group, and to use the port for transmission.

active—Enables LACP only if a LACP device is detected. It places the port into an active negotiating state in which the port starts negotiations with other ports by sending LACP packets.

passive—Enables LACP on the port and places it into a passive negotiating state in which the port responds to LACP packets that it receives, but does not start LACP packet negotiation.

 

 

bootp packets are dropped on switch

We had the problem, that bootp packets from an IBM p720 client, which should get an image from an IBM NIM server, were dropped on the switch where the client was connected to. I could proof this with a SPAN port on the local switch. The switch which was used was a cisco 3750G stack with 15.02 ios release.

The ibm p720 client had a fixed ip address, as also the IBM NIM server and the client was configured to use the IBM NIM server ip address, so the packets were unicast packets.

The reason why those packets were dropped is dhcp snooping feature on the cisco switches. This feature is used to prevent the network from so called spurious DHCP server, which are dhcp servers which exist in your network without your knowledge. Here an abstract from the cisco configuration guideline:

If a Layer 2 LAN port is connected to a DHCP server, configure the port as trusted by entering the ip dhcp snooping trust interface configuration command.

If a Layer 2 LAN port is connected to a DHCP client, configure the port as untrusted by entering the no ip dhcp snooping trust interface configuration command.

For more details see: Configuring DHCP Features and IP Source Guard

To prevent the switch from dropping the packets from the bootp client, we had to configure the NIM server port with „ip dhcp snooping trust“ as also the client port.

Bootp was designed prior to dhcp and uses the same ports (UDP 67, 68) as dhcp. Based on lack of time, I could not find the exact reason for the packet drop, the packet validaiton chapter from the cisco link above didn’t bring fast enlightment, why we also had to configure the client ports with „ip dhcp snooping trust“.

 

 

 

 

Windows thumbnail cache size

Recently I had the problem because windows is not able to cache the thumbnails for a folder with a hugh size of pictures. I found some registry values which helps me to increase this size.

The following RegEdit script will change the „Max Cached Icons“ from 512 to 4095. I tested it with windows 7 and it works for pictures and movies. Just copy/paste it to a file called „thumbnail_cache.reg“ and execute it with a double click on it.

REGEDIT4

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\explorer]
„Max Cached Icons“=“4095“

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\explorer\Advanced\IconCache]
„Text“=“Icon Cache Groesse“
„Type“=“group“
„Bitmap“=“SHDOC401.DLL,6“
„HelpID“=“update.hlp#51140“

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\explorer\Advanced\IconCache\Small]
„RegPath“=“Software\\Microsoft\\Windows\\CurrentVersion\\Explorer“
„Text“=“1024 Icons“
„Type“=“radio“
„CheckedValue“=“1023“
„ValueName“=“Max Cached Icons“
„DefaultValue“=“4095“
„HKeyRoot“=dword:80000002
„HelpID“=“update.hlp#51140“

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\explorer\Advanced\IconCache\Medium]
„RegPath“=“Software\\Microsoft\\Windows\\CurrentVersion\\Explorer“
„Text“=“2048 Icons“
„Type“=“radio“
„CheckedValue“=“2047“
„ValueName“=“Max Cached Icons“
„DefaultValue“=“4095“
„HKeyRoot“=dword:80000002
„HelpID“=“update.hlp#51140“

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\explorer\Advanced\IconCache\Large]
„RegPath“=“Software\\Microsoft\\Windows\\CurrentVersion\\Explorer“
„Text“=“4096 Icons“
„Type“=“radio“
„CheckedValue“=“4095“
„ValueName“=“Max Cached Icons“
„DefaultValue“=“4095“
„HKeyRoot“=dword:80000002
„HelpID“=“update.hlp#51140“

server doesn’t respond to ping though he receives it

I had following scenario:
client in client vlan
server multihomed in client vlan and server vlan with SLES 11.2 (I know that this is bad!)

the server didn’t respond to the ping from the client when the client pinged the srv vlan ip of this server. (ping came in on iface of the srv vlan but the server never send a reply)
I could proof this through tcpdump. After opening a service request at novell, the rp_filter was the solution. If this filter is set to one, the server won’t respond depending on the setting of this filter.
Set to 0 (deactivated) the server starts responding to the ping. For details please see:

http://ifup.org/2011/02/03/reverse-path-filter-rp_filter-by-example/

# enable route verification on all interfaces
net.ipv4.conf.all.rp_filter = 1