[c-nsp] Re-thinking (remembering) how a switch operates

[Jeff Kell]

Network.Security wrote:
>  And somewhere in there is says to tweak either the L3 to match L2 or
> vice-versa.  In a chat with Cisco, it was highly recommended to match L3
> to 5 minutes...the L2 default.  Apparently tests showed no issues even
> with older cat5k gear with loads (>40,000 ARP entries if I remember
> right) of ARP entries.

L2 default aging time is 300 secs/5 minutes.  L3 default aging time is
14400 secs/4 hours!

CCO has some discussion about a similar situation experienced with VoD
(video on demand) clients.  From that page:

> Because the data flow in VoD is unidirectional, the MAC address table
> for each Gigabit-Ethernet port connected to an edge QAM device
> eventually times out and causes data bound for that device to get
> flooded to all ports. To get around this, set the Address Resolution
> Protocol (ARP) timeout for that port (or VLAN) to a value less than
> the value for mac-address-table aging-time . Because the default
> value of aging-time is 300 (seconds), the ARP timeout can be set to
> 150, as follows: arp timeout 150 .

> http://www.cisco.com/en/US/customer/netsol/ns341/ns396/ns159/ns333/networking_solutions_release_note09186a008020213c.html

Jeff