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Previously, when using the "dhclient" DHCP protocol client on a host with two network interfaces connected to the same subnet, "DHCPREQUEST" packets were only being sent to one of the interfaces. Consequently, the IP address lease of the other interface was not being renewed.
With this update, "dhclient" sends "DHCPREQUEST" and "DHCPRELEASE" packets to both interfaces, even if they are on the same subnetwork.
DescriptionPatrick Laimbock
2014-12-26 13:26:43 UTC
Created attachment 973198[details]
Patch to dhclient: Unicast requests sent on "wrong" interface
Description of problem:
dhclient fails to renew IP addresses from the same subnet on a VM with 2 nics (eth0, eth1) configured for dhcp via network-service. The DHCPDISCOVERY stage works fine and both eth0 and eth1 will get an IP address. But while in renewing state and with similar routes on each interface, eth1 seems to send its DHCPREQUEST through the eth0 interface and renewal for eth1 fails while renewal for eth0 succeeds.
Version-Release number of selected component (if applicable):
CentOS 7 (up-to-date)
dhcp-4.2.5-27.el7.centos.2
How reproducible:
Add VM with EL7 and at least 2 nics, disable NetworkManager, enable network-service, configure nics for dhcp in ifcfg-eth{1,2}, configure dhcp server to assign an IP address to both nics from the same subnet, start VM, see initial DHCPDISCOVERY succeed for eth0 and eth1, see all subsequent renewals via DHCPREQUEST fail for eth1 (and still succeed for eth0).
Steps to Reproduce:
1. add VM with 2 nics, enable network-service + dhcp, start VM
2. after initially succesfully obtaining 2 leases wait for renewal
3. renewal fails for eth1, succeeds for eth0
Actual results:
Renewal fails for eth1
Expected results:
Renewal succeeds for eth1
Additional info:
The problem was reported several times on the dhcp mailing list but no response from ISC (examples: https://lists.isc.org/pipermail/dhcp-users/2013-February/016398.html and https://lists.isc.org/pipermail/dhcp-users/2014-April/017835.html).
A patch to fix this issue by Guillaume Nault is referenced here:
https://community.ubnt.com/t5/EdgeMAX/WAN-dropped-DHCP-renew-fixes-it/m-p/783774
I contacted Guillaume, received the latest version of his patch and rebased it on the 4.2.5 release, added it as the latest patch in the dhcp spec file, rebuilt it, tested the new dhclient on current CentOS 7 and renewal now also succeeds for eth1.
Please let me know if you need more information.
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://rhn.redhat.com/errata/RHEA-2015-2251.html