Question about "no ip gratuitous-arp" command in IOS

[CHRISTINE BERNS]

Does the "no ip gratuitous-arp" command affect gratuitous arps sent by the router (for example, when hsrp causes a secondary router to assume role of primary) or does it affect gratuitous arps received by the router (for example, gratuitous arps with the spoofed IP address of the router).

[Richard Burts]

I do not have direct experience with this command. But I think that the documentation is clear that the command restricts the router sending gratuitous arp and does not affect the router receiving gratiutous arp.

The documentation is fairly clear that its restriction on gratiutous arp is a restriction on sending gratiutous arp when a remote client has learned an IP address via PPP negotiation and the address is in a local address pool. Assuming that this part of the documentation is accurate it would have no affect on the router sending gratiutous arp in HSRP takeover situations.

HTH

Rick

[trippi]

So it is safe to assume that the command will not break HSRP configured on the same router?

[Richard Burts]

As I said in my previous post, if we assume that this part of the documentation is accurate then yes it is safe to assume that using the command will not break HSRP.

HTH

Rick

[mgaven]

On three 2600 routers in my network I configured the "no ip gratuitous-arp" global command and they have continued sending gARP messages, I don´t understand what that command does...

[Richard Burts]

The command reference is pretty clear that this command is about what the router does when it is assigning addresses from a pool of addresses. Is that the situation on your 2600 routers?

see this link for details:

http://www.cisco.com/en/US/docs/ios-xml/ios/ipaddr/command/ipaddr-i3.html#wp2123221095

In what circumstance is the router sending the gratuitous arp?

HTH

Rick

[mgaven]

Richard, I have the routers connected to a 2960G switch.

All of them are performing a static nat to the same IP address (a DNS server) and all the time are sending gARP about that.

The log files of the routers are full of this message:

Aug  5 11:41:39.509: %IP-4-DUPADDR: Duplicate address (X.X.X.X , the natted IP) on VlanXXX, sourced by xxxx.xxxx.xxxx

The inclussion of the "no ip gratuitous-arp" don´t solve the problem, but works fine when I create a static ARP entry for the natted IP with the MAC address of the inside interface.

Martin.

[Richard Burts]

Martin

The no ip gratiutous-arp command is not intended to do what you were trying to get it to do. The static arp is a much better solution.

HTH

Rick

[maraz]

Hello,

Many people are not aware of that there is two different commands that does different things. The other command not mentioned above is:

ip arp gratuitous (or no ip arp gratuitous, if you want to disable it.) Gratuitous arps are needed or necessary in many environments so I would not disable right away...

Best Regards

Robert Maras

[maraz]

Hello,

Many people are not aware of that there is two different commands that does different things. The other command not mentioned above is:

ip arp gratuitous (or no ip arp gratuitous, if you want to disable it.) Gratuitous arps are needed or necessary in many environments so I would not disable right away...

Best Regards

Robert Maras