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Archange

Package Maintainer (PM)

Registered: 2014-08-17

Posts: 40

[SOLVED] On a certain network dhclient is working, but dhcpcd is not

Hi there,

I have a strange issue were, when connected to a certain network, I’m unable to acquire a DHCP lease with dhcpcd while dhclient works OOTB. I’m not even sure how to debug this, but I’ve started looking at request with Wireshark and it seems that dhcpcd sends vendorid (60) and clientid (61) while dhclient seems to not send any of those. I’ve figured out how to make dhcpcd not send vendorid, but fail to do so for clientid.

Also, do you have anything else in mind that I should check/test?

Thanks a lot!

Last edited by Archange (2016-09-27 14:53:58)

Archange

Package Maintainer (PM)

Registered: 2014-08-17

Posts: 40

Re: [SOLVED] On a certain network dhclient is working, but dhcpcd is not

Oh, and also, I have no way to reach the network admins (or any form of local assistance) obviously.

rsmarples

Member

Registered: 2009-05-12

Posts: 287

Re: [SOLVED] On a certain network dhclient is working, but dhcpcd is not

Comment out both duid and clientid in dhcpcd.conf

Then tell your admins to implement an RFC compliant DHCP server.

Archange

Package Maintainer (PM)

Registered: 2014-08-17

Posts: 40

Re: [SOLVED] On a certain network dhclient is working, but dhcpcd is not

Thanks, that worked!:) Regarding admins, I’m not even going to try… Until precisely y-day, the webmail server they manage provided exactly these ciphers:

TLS_RSA_WITH_RC4_128_MD5
TLS_RSA_WITH_RC4_128_SHA
TLS_RSA_WITH_3DES_EDE_CBC_SHA
TLS_RSA_WITH_DES_CBC_SHA
TLS_RSA_EXPORT_WITH_RC4_40_MD5
TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5

With the strongest of those now having a known attack against it and being tentatively phased out in some clients, some users started being unable to connect to the services and finally the admins upgraded it to almost state-of-the-art ciphers. But I had opened and repeated my request already several months ago, without any effect or answer. So, if they’re that much not concerned about that huge security issue, I don’t know how I could make them change their DHCP server…

So… Bonus question: is there an easy way to configure dhcpcd like that just for this connection? (I’m using netctl currently, but I’m fine switching to systemd-networkd or bare dhcpcd if needed)

rsmarples

Member

Registered: 2009-05-12

Posts: 287

Re: [SOLVED] On a certain network dhclient is working, but dhcpcd is not

Hmmmm, not really no.
You can enable them for each interface, but not disable.

# No duid or clientid in global section

interface eth0
duid

interface eth1
clientid

interface eth2
# no id sent

Archange

Package Maintainer (PM)

Registered: 2014-08-17

Posts: 40

Re: [SOLVED] On a certain network dhclient is working, but dhcpcd is not

OK, will live with that (I essentially use wifi connection everywhere but the incriminated one is wired). Thanks again for your help!

rsmarples

Member

Registered: 2009-05-12

Posts: 287

Re: [SOLVED] On a certain network dhclient is working, but dhcpcd is not

If you file a ticket on my site, I will try and find a way of enabling you to make it easier
Maybe add a patch so the below works:

interface eth0
# Stop dhcpcd from sending a client identifier for this interface
nooption dhcp_client_identifier