CISCO EA2700 not connecting after power outage

CISCO EA2700 not connecting after power outage

Hey  guys, I’ve been experiencing some issue with a new Cisco router I bought for my house (EA2700) seems that after a power outage it cannot gain public IP from the modem, so here is what I found out, might be useful for other people.My setup, EA2700 connected through the WAN interface to a Motorola SB5101 Modem. My EA2700 doesn’t get an IP after both boxes are rebooted (after a power failure for example). The only happens ONLY if the Motorola comes up first than the Linksys router. And my ISP has also this thing of allowing only 1 MAC to be connected.

The thing is that the EA2700 virtualizes its MAC addresses, one for the WAN interface, one for the 2.4g wireless interface and another for the 5g wireless interface. After checking those three, in my case they were ending in:

  • WAN MAC: :00:20
  • 2.4g MAC: :00:21
  • 5g MAC: :00:22

Too neat to be real, so after thinking and doing some test I figured this is what is happening:

  1. The Motorola modem comes up
  2. The EA2700 with its native WAN MAC address comes up
  3. The Motorola modem will learn the native MAC address from the EA2700 and “assign” it the public IP from the ISP
  4. Then the EA2700 will “hardcode” the new MAC address into the WAN port. And here is where the Motorola device decides not to talk to the router anymore.

I have tested this, really simple test, shutdown both devices, power on the EA2700 first, once it is up and running, power on the Motorola device. No issues.

Now, the question is how to solve this. What I did, I “cloned” into the WAN port MAC’s the original MAC. How to get it?

  1. Turn on the Motorola modem
  2. Turn on the EA2700
  3. Unplug the EA2700 from the network port on the modem and plug a computer to the modem (DO NOT REBOOT THE MODEM AT ANY POINT IN TIME, WE NEED TO KNOW THE MAC ADDRESS THAT’S BEEN LEARNED BY THE MODEM)
  4. Set an IP on your computer’s wired interface on the range of 192.168.100.0/24 (i.e.: 192.168.100.32/24)
  5. Use a browse to navigate into 192.168.100.1 (I think all Cable Modems have the same IP)
  6. Check on the Addresses menu (at least for the SB5101, for another look where are the learned MAC Addresses) on the Known CPE MAC Addresses table, there should be 1 labeled as Self, which is the modem itself, and another one labeled as learned. That’s what you are looking for. In my case it was exactly the same as the virtualized MAC’s the only difference was the last octet (:1f).
  7. Clone that MAC into the WAN port, that will make it for you.

Hope this helps guys!

Hernán

2 Replies to “CISCO EA2700 not connecting after power outage”

  1. Hernan, thanks for sharing this data, was really helpfull to find a solution to this.

    Following your steps, found out that if you use the clone mac addres function, the EA2700 would not propperly inform that mac address to the modem in the wan port.

    Lucky you could get acces to the modem status panel (i couldn’t as that is blocked by my isp)

    So first tried to change the last octect to :1F like happenned to you, unlucky..
    My only option was: DISABLE MAC ADDRESS CLONING

    and THAT did the trick!

    Allready informed this to the guys at Linksys. We’ll see if they fix this with a future firmware update.

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