# carrier acquired, dhcpcd up, carrier lost - again [SOLVED]

## daddio

I'm building a new gentoo box intended as a router/firewall, but am having some troubles with elementary networking 

(never mind the bridging, filtering  and stuff. I haven't even tried to do that yet.)

When I boot the box from systemrescueCD, which is based of a recent gentoo, my e1000 connection to my cable modem works great, but when I reboot into native gentoo, the link will not stay live!

Maybe this should go under "Installation" thread.  I don't know.

Here is a snippet of the logs. It does this over and over until I take the interface down. I have noticed that /etc/resolv.conf never seems to get filled with dns info, so maybe dhcp is not getting all the way up

```

Feb 22 04:03:41 triceratops kernel: [24226.538378] e1000: eth0 NIC Link is Up 100 Mbps Full Duplex, Flow Control: RX

Feb 22 04:03:41 triceratops kernel: [24226.538530] ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready

Feb 22 04:03:41 triceratops dhcpcd[8091]: eth0: carrier acquired

Feb 22 04:03:41 triceratops dhcpcd[8091]: eth0: rebinding lease of 71.195.255.75

Feb 22 04:03:41 triceratops dhcpcd[8091]: eth0: acknowledged 71.195.255.75 from 68.87.66.21

Feb 22 04:03:41 triceratops dhcpcd[8091]: eth0: checking for 71.195.255.75

Feb 22 04:03:46 triceratops dhcpcd[8091]: eth0: leased 71.195.255.75 for 320683 seconds

Feb 22 04:03:46 triceratops kernel: [24231.610919] e1000: eth0 changing MTU from 1500 to 576

Feb 22 04:03:46 triceratops dhcpcd: eth0: MTU set to 576

Feb 22 04:03:47 triceratops dhcpcd[8091]: eth0: carrier lost

Feb 22 04:03:47 triceratops dhcpcd: eth0: MTU restored to 1500

Feb 22 04:03:47 triceratops kernel: [24231.699931] e1000: eth0 changing MTU from 576 to 1500

Feb 22 04:03:48 triceratops kernel: [24233.334381] e1000: eth0 NIC Link is Up 100 Mbps Full Duplex, Flow Control: RX

Feb 22 04:03:48 triceratops kernel: [24233.334535] ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready

Feb 22 04:03:48 triceratops dhcpcd[8091]: eth0: carrier acquired

Feb 22 04:03:48 triceratops dhcpcd[8091]: eth0: rebinding lease of 71.195.255.75

Feb 22 04:03:48 triceratops dhcpcd[8091]: eth0: acknowledged 71.195.255.75 from 68.87.66.21

Feb 22 04:03:48 triceratops dhcpcd[8091]: eth0: checking for 71.195.255.75

Feb 22 04:03:53 triceratops dhcpcd[8091]: eth0: leased 71.195.255.75 for 320676 seconds

Feb 22 04:03:53 triceratops kernel: [24238.491916] e1000: eth0 changing MTU from 1500 to 576

Feb 22 04:03:53 triceratops dhcpcd: eth0: MTU set to 576

Feb 22 04:03:53 triceratops dhcpcd[8091]: eth0: carrier lost

Feb 22 04:03:53 triceratops dhcpcd: eth0: MTU restored to 1500

Feb 22 04:03:53 triceratops kernel: [24238.581934] e1000: eth0 changing MTU from 576 to 1500

Feb 22 04:03:55 triceratops kernel: [24240.214399] e1000: eth0 NIC Link is Up 100 Mbps Full Duplex, Flow Control: RX

```

ethernet drivers for e1000 and r8169 are built into the kernel.

I'm rebulding the kernel with the network drivers as modules, but I'm having a hard time imagining that is the problem.

Is is possible I have forgotten some essential step?

I suppose it is possible something is wrong with the cable modem, but it seems to work fine with systemrescueC, (which uses networkmanager)

The last piece of the puzzle, is I also have a laptop which experiences the same symtoms. But with the laptop, I can see the light go off on the NICLast edited by daddio on Thu Feb 24, 2011 1:06 am; edited 1 time in total

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## UberLord

You have two issues:

1) Your upstream DHCP server wants to set an MTU of 576. This is probably an error at their end.

2) Your network driver is buggy as setting the device MTU should not also bring the link down/up (which is triggering this infinite loop)

The workaround is to get dhcpcd to ignore MTU from the DHCP server by commenting out the line "option interface_mtu" in /etc/dhcpcd.conf, which is documented in dhcpcd.conf(5)

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