gratuitous-arps

jabercromby · ‎08-11-2009

It appears (to me at least) that the documentation (Command References) and command lookup tool provide elusive/and almost contradict each other on what the default behavior is) for:

no ip gratuitous-arps

ip gratuitous-arps

On top of that it appears that Cisco does not support these

commands on certain IOS based Catalysts.

I thought (most likely incorrect) that 'ip gratuitous-arps' were enabled by default through 12.2?

12.3 on - no ip gratuitous-arps was the default

end of story.

Can someone please provide accurate information on this

or point me in the right direction?

Jim Abercromby

Lucien Avramov · ‎08-11-2009

Use this command reference for IOS:

http://www.cisco.com/en/US/docs/ios/ipaddr/command/reference/iad_arp.html#wp1013090

For Catalyst, the feature dynamic arp inspection does this:

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_25_see/configuration/guide/swdynarp.html

jabercromby · ‎08-11-2009

Let me make sure I have this straight

For IOS/Router platforms = 'ip gratuitous arps'

disabled by default since 12.2

For Catalyst/Switch (MLS) etc. = 'ip arp inspection'

This is disabled by default too.

So if I am looking to see if a catalyst switch is

filtering/restricting gratuitous arps

'ip arp inspection filter vlan' commands

filtering specific vlans would have to be configured.

YES or NO?

Lucien Avramov · ‎08-11-2009

1. NO: For IOS/ROUTERS, by default, if no command is entered:

Gratuitous ARP messages are NOT sent out when the client receives the address from the local address pool.

2. YES for Catalyst, Dynamic Arp Inspection, not enabled by default