WRT54G not working, ARP cache poisoning?

Discussion in 'Networking Issues' started by rep164, Mar 9, 2011.

  1. rep164

    rep164 Networkin' Nut Member

    Hi all,

    Hope this isn't a redundant post but I Googled the whole website for "ARP cache" and couldn't find anything similar so... if you have any advice on what could be causing the following problems w/my wireless router, please let me know!

    It's a pretty basic residential setup... just one wireless router that my 2 roommates and I connect to on our laptops (1 Mac & 2 PCs). For the last couple days the router (WRT54G) hasn't been working--my roommates & I can each see the wireless network & connect to it on our laptops, but once you're on the network you can't actually connect to the internet. But if I plug the modem directly into my laptop w/an Ethernet cable, I can get on the internet. So it's basically a problem with the wireless router connecting to the internet. My roommate thinks it may be related to the power going on & off several times Sunday night during a blizzard just because it happened at the same time, but we're not sure.

    Monday I installed Norton Antivirus on my Macbook for the first time (coincidental timing, I wanted to do a virus scan because it had been acting funky... but it was unrelated hard drive issues. ...it's been a good week.) And just today I noticed that whenever I am connected to the wireless router I am bombarded w/"ARP Cache Poison" alerts in Norton... by "bombarded," I mean like faster than one per second. When I connect straight to the modem & skip the router, I don't get the alerts.

    I am not a hardcore techie so I did a little research into WTF an ARP Cache Poison is, but am still confused about if this could be causing/related to our router problems (sure seems like it but I guess it is hard to know for sure since I installed Norton after the router problems started), and how to fix it.

    Would it help to know what MAC address the "ARP Cache Poisons" are coming from, and/or the IP & MAC addresses that I see in my ARP cache, or is that not stuff I am supposed to be putting out on the internet for all to see? (haha, I know I sound like such a clueless old person... :)) I will say that when I am connected to the wireless router, my ARP cache shows no MAC address associated with my router IP, it just says (incomplete). It also shows "ff:ff:ff:ff:ff:ff" as the MAC address associated w/another IP that is similar to my router IP but not the same. Those are the only 2 things in the ARP cache.

    Also, even when I am connected to the wireless network but the router is unplugged from the modem, the "cache poison" notifications continue to pile up. Oh and final additional fact, when I am connected to the wireless network & type in my router IP to try to look at the router settings in my browser, I can't... nothing happens/the page doesn't show.

    Any thoughts?? Or anything else that would be helpful to know? I am pretty clueless here. Thanks in advance!
  2. Toxic

    Toxic Administrator Staff Member

    right what type of modem is your ISP supplying? ADSL or Cable?

    if it is a cablemodem, please turn it off, then back on again. once the connection lights gone solid, power off/on your WRT54G and see if that fixes your connection to the net.

    Cablemodems usually issue only one IP address, which works on your laptop. when you add the router the CM sees a new device but doesn't issue it a new IP. a reboot of the CM usually fixes this.
  3. rep164

    rep164 Networkin' Nut Member

    Weirdest thing...

    My ISP is Verizon and it's a Westell 6100G combination DSL modem/router, not a cable modem. But your question prompted me to remember that when I first set it up after I moved I had to do change the Westell to "bridge mode" so it just acted as a modem not as a router, so that I could add the wireless router to the setup... so I went back in and put it in bridge mode again, and even then it didn't work right away but I did a bunch of different resetting and unplugging and replugging in different configurations of the modem, router, & my laptop... and somehow it works now. Ugh. Thanks for your help!
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