How To – Enable Wake On Lan using a Cisco ASA

I wrote instructions for how to configure Wake On Lan forwarding using a Cisco IOS device, this article will focus on how to configure a Cisco ASA firewall.

Wake On LAN is an Ethernet standard that allows for a device to be powered on when receiving a specially crafted “magic packet”. The “magic packet” is a broadcast frame consisting of 6 bytes of 255 (FF FF FF FF FF FF) followed by sixteen repetitions of the 48-bit MAC address. Turned off computers receiving the broadcast don’t actually process the message up the protocol stack, they are just looking out for a matching 102-byte string.

From what I can tell, unlike Cisco IOS the ASA doesn’t support “IP Directed Broadcasts”, likely to prevent Smurf Attacks. However with some clever NAT rules it’s possible to achieve something similar by using NAT to translate the inbound unicast packet and send it on to the broadcast address for your internal subnet.
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Zyxel GS1910 Fan Replacement

Not too long ago I purchased a Zyxel GS1910-24HP for my home network. It suited my requirements well (12-24 ports, PoE, Gigabit, Rack-mountable and manageable). Unfortunately once I got it powered up I noticed how loud it was. Even though it sits in a small rack in my loft, it was still too loud. The Zyxel website has an FAQ article which states the noise could range from 28dB to 48dB!

Thankfully the GS1910 comes with some fairly standard fans, my model shipped with two 3-pin SUNON 80mm fans (model number KDE1205PHV3). Replacing these turned out to be fairly straightforward and in my case resulted in only a marginal increase in temperature. Before replacement, temperatures were as follows:

Temperature (°C)	Current	Threshold	Status
MAC Temperature		32	85		Normal
Board Temperature	30	85		Normal
PHY Temperature		28	85		Normal

FAN	Speed (RPM)	Current	Threshold	Status
FAN1	8640		500			Normal
FAN2	5040		500			Normal

After shopping around I settled on two Fractal Design Silent Series R2 40mm Case Fan as reasonable noise to airflow compromise. The one thing the original SUNON fans had going for them was their CFM, 13CFM compared to just 4.5CFM on the Fractal fan’s.
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Cisco time synchronisation & summer time

Having accurate time configured on Cisco routers is important, if for nothing else being able to look through log files and understand when something happened is imperative. Configuring time on Cisco routers requires three different configuration elements:

  • Configuring an external time source, usually NTP
  • Configuring the device to adjust for summer time/daylight savings
  • (Optionally) using the adjusted time in debugging and logs

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