bin/149351: DHCP can make one interface to have multiple IP addresses

Jin Guojun jguojun at
Fri Aug 6 06:00:18 UTC 2010

>Number:         149351
>Category:       bin
>Synopsis:       DHCP can make one interface to have multiple IP addresses
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Fri Aug 06 06:00:17 UTC 2010
>Originator:     Jin Guojun
>Release:        RELEAE-8.1
When DHCP server is down, manually configured rl0 to an IP -- -- for temporarily use.
As DHCP came back and assigned  another IP on the rl0, now NIC is down
due to two conflict IP addresses.

rl0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
        ether 00:40:f4:d1:23:9a
        inet netmask 0xffffff00 broadcast
        inet netmask 0xffffff00 broadcast
        media: Ethernet autoselect (100baseTX <full-duplex>)
        status: active
plip0: flags=8810<POINTOPOINT,SIMPLEX,MULTICAST> metric 0 mtu 1500

DHCP should work as ifconfig to replace the old IP with new IP, not set additional IP on an interface.
Configure an interface (say rl0) to use DHCP.
Boot machine with network Ethernet cable unplugged.
After machine boot up, ifconfig rl0 to some IP not in DHCP range.
Plug in Ethernet cable and wait for a while to let DHCP active.
You will see two IPs on the Ethernet interface.


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