Arch Linux

llabtaem

Member

Registered: 2019-08-14

Posts: 5

[SOLVED] Using netctl for DHCP Fails - Cisco Switch

Hello,

I was wondering if someone could explain to me what is going on with my Arch installs? Below is an outline of what is happening and what I did to bandage it. I may be on the spectrum, please be gentle.

1. I had two (2) Arch installs using a netctl DHCP profile file connected to a Cisco unmanaged switch. Some little cheap 5 port switch.

2. I moved them off the unmanaged switch and onto a Cisco Catalyst 3560G 48 port managed switch and lost network.

3. I used the tools that are at my disposal like journalctl, dmesg, systemctl, as well as netctl to see if the profile was active. The only error I could find was using journalctl and it was telling me that the service dhcpcd failed. I tried starting it with

   sudo systemctl start dhcpcd@enp5s0.service

   but that did not work.

4. Upon playing around trying to figure out why this all of a sudden happened. I discovered that disabling and stopping the netctl DHCP profile and creating a netctl static profile worked, I got a network connection.

All my other machines, both physical and virtual. A mixture of Windows and other Linux OSes did not experience this issue. The Cisco switch is bare minimum, only vlan 1 (I know, I should create a new vlan and move all the ports to that vlan) is setup with an IP and subnet mask. I also set the default gateway and then from the switch I tested it using a ping to Google's DNS servers with success. No ports on the switch were configured, they are all defaulted.

I am teaching myself more about networking, but I am really stumped on this one. The only explanation I can think of is I am missing a package on the Arch boxes as it is only these installs I am having this strange issue with.

Can someone please explain to me what it is I am missing? I am really not worried about keeping these Arch boxes with static IPs. I mean, what's it hurting right? I just want a better understanding of what is going on. I need to understand it.

Any insight would be greatly appreciated it. Thank you for your time.

Last edited by llabtaem (2019-08-17 00:34:04)

Lone_Wolf

Member

From: Netherlands, Europe

Registered: 2005-10-04

Posts: 11,911

Re: [SOLVED] Using netctl for DHCP Fails - Cisco Switch

try disabling / stopping the netctl service and (as root) run manually

dhcpcd

Post the terminal output.

Last edited by Lone_Wolf (2019-08-14 14:02:16)

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seth

Member

Registered: 2012-09-03

Posts: 50,933

Re: [SOLVED] Using netctl for DHCP Fails - Cisco Switch

A list of usual suspects:

- Search for rogue dhcp servers

sudo nmap --script broadcast-dhcp-discover

- try dhclient and/or
- use clientid instead of duid (see /etc/dhcpcd.conf)

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pkill

Member

Registered: 2019-08-16

Posts: 4

Re: [SOLVED] Using netctl for DHCP Fails - Cisco Switch

1. I moved them off the unmanaged switch and onto a Cisco Catalyst 3560G 48 port managed switch and lost network.

Is spanning-tree portfast enabled for that port?

interface GigabitEthernet0/x
 spanning-tree portfast

llabtaem

Member

Registered: 2019-08-14

Posts: 5

Re: [SOLVED] Using netctl for DHCP Fails - Cisco Switch

Sorry everyone for the late response and thank you for yours.

try disabling / stopping the netctl service and (as root) run manually

dhcpcd

Post the terminal output.

The output of the terminal:

    dev: loaded udev
    no interfaces have a carrier
    forked to background, child pid 2266

A list of usual suspects:

- Search for rogue dhcp servers

sudo nmap --script broadcast-dhcp-discover

- try dhclient and/or
- use clientid instead of duid (see /etc/dhcpcd.conf)

No rouge DHCP clients

Need to contunine looking into dhclient and clientid.

1. I moved them off the unmanaged switch and onto a Cisco Catalyst 3560G 48 port managed switch and lost network.

Is spanning-tree portfast enabled for that port?

interface GigabitEthernet0/x
 spanning-tree portfast

No spanning-tree portfast on the port. As I am still learning my knowledge may be wrong but isn't this when you trunk switches? This is how you get them to communicate?

Again, thank you all for you help. I have some things to dig into and try now.

Last edited by llabtaem (2019-08-17 00:13:42)

llabtaem

Member

Registered: 2019-08-14

Posts: 5

Re: [SOLVED] Using netctl for DHCP Fails - Cisco Switch

I think I know what the issues was. I didn't have the dhclient package installed. Once installed it, I started dhcpcd via the following command:

 sudo systemctl start dhcpcd 

I then got an IP from my DHCP server.

When I went to uninstall dhclient just because I like to verify the solution. I received a warning that netctl needed it for DHCP. I think it is safe to assume this was my issue, a missing package.

Thank you all so much for your help! I cannot thank you enough!

Last edited by llabtaem (2019-08-17 00:36:41)