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Hard coding mac address

rickyt00
Level 1
Level 1

‎09-07-2004 07:33 AM - edited ‎03-02-2019 06:17 PM

We recently had a problem where a user accidently set the ip address of a printer to the default gateway their vlan. Of course this brought everyone in the vlan down, and once I set the mac address to the real default gateway it worked fine. My question is that is this static entry going to stay in the arp table even after a reboot. Right now when I say show arp I am getting this entry. Have in mind I am running HSRP.

Internet 10.10.247.253 - 00b0.8e83.8470 ARPA Vlan247

Internet 10.10.247.254 - 00b0.8e83.8470 ARPA

The fact that it doesn't seem to be associated with a vlan worries me. Is this ok? Thanks

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4 Replies 4

smif101
Level 4
Level 4

‎09-07-2004 07:54 AM

Yes the static entry will stay in the arp table but I don't recommend doing that. I would normal it up and just ensure that the people are trained properly. The best way to have fixed the problem would have been to set the printer to the proper IP address and then just clear the arp table.

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rjackson
Level 5
Level 5
In response to smif101

‎09-07-2004 08:14 AM

I dont see how setting the static entry in the router would help. The problem was that the printer was answering the users ARPs for the gateway address. So the problem is in the ARP table of the end users pc. You do not want to hard code the routers mac (or HSRP mac) in every pc. You just have to get control over your network so people are not adding devices without some sort of control process.

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rickyt00
Level 1
Level 1
In response to rjackson

‎09-07-2004 10:03 AM

Well when I first realized what happened I went to the printer and powered it off and reboot the machines. And it still didn't work. So I went to a pc in another vlan, and looked at the arp table, and saw that the mac address of the 10.10.247.254 was the mac address of the printer. And as soon as I set a static entry it fixed the problem. My problem is that this is a campus network, and we were seeing problems like this last year, from angry students or someone like that.

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milan.kulik
Level 10
Level 10
In response to rickyt00

‎09-07-2004 11:57 PM

Hi,

haven't you considered to involve IP Source Guard to your network?

(See http://www.cisco.com/univercd/cc/td/doc/product/lan/cat4000/12_1_19/config/dhcp.pdf, e.g.)

I know this is a pretty new feature and I'd like to find somebody with practical experience with it.

Regards,

Milan

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