#554150 Failover peer separation, revisited again

Package:
isc-dhcp-server
Source:
isc-dhcp
Description:
ISC DHCP server for automatic IP address assignment
Submitter:
Thomas R Björklund
Date:
2026-08-05 17:33:37 UTC
Severity:
normal
#554150#5
Date:
2009-11-03 10:32:51 UTC
From:
To:
isc-dhcpd in a failover setup tries to reconnect to its peer for about two minutes, then it stops and the two servers wont resync until one of them are restarted.

This causes a problem when the two servers are deployed in a large network where they can be separated by outages/planned maintance for over 2 minutes. After a couple of hours they are not able to give out any leases, the logfile says "Peer holds all free leases" in both servers.

This is easily reproduceable by setting up two servers and then blocking the connectivity between them.

I ran into this problem recently and when I searched for it I found this upstream bugreport from november 2008 on the dhcp-users mailinglist: https://lists.isc.org/pipermail/dhcp-users/2008-November/007433.html

In my test setup I used two servers on the same LAN and blocked failover communication with iptables


Nov  2 16:41:59 dhcptest-primary dhcpd: failover peer peer: peer moves from communications-interrupted to normal

The servers both start in state "normal", then I block the communications and also log the packets.

Nov  3 11:18:08 dhcptest-primary dhcpd: Copyright 2004-2008 Internet Systems Consortium.
Nov  3 11:18:08 dhcptest-primary dhcpd: All rights reserved.
Nov  3 11:18:08 dhcptest-primary dhcpd: For info, please visit http://www.isc.org/sw/dhcp/
Nov  3 11:18:08 dhcptest-primary dhcpd: Wrote 0 leases to leases file.
Nov  3 11:18:08 dhcptest-primary dhcpd: failover peer peer: I move from communications-interrupted to startup
Nov  3 11:18:08 dhcptest-primary dhcpd: failover peer peer: peer moves from normal to communications-interrupted
Nov  3 11:18:08 dhcptest-primary dhcpd: failover peer peer: I move from startup to normal
Nov  3 11:18:08 dhcptest-primary dhcpd: balancing pool 6ae8e0 192.168.10.0/29  total 1  free 1  backup 0  lts 0  max-own (+/-)0
Nov  3 11:18:08 dhcptest-primary dhcpd: balanced pool 6ae8e0 192.168.10.0/29  total 1  free 1  backup 0  lts 0  max-misbal 0
Nov  3 11:18:08 dhcptest-primary dhcpd: failover peer peer: peer moves from communications-interrupted to normal

At 11:18:2x I use iptables to block incoming and outgoing packets to the secondary server.

Nov  3 11:18:28 dhcptest-primary kernel: IN= OUT=eth0 SRC=192.168.1.1 DST=192.168.1.2 LEN=64 TOS=0x00 PREC=0x00 TTL=64 ID=43973 DF PROTO=TCP SPT=32947 DPT=520 WINDOW=365 RES=0x00 ACK PSH URGP=0
Nov  3 11:18:28 dhcptest-primary kernel: IN=eth0 OUT= MAC=00:16:3e:02:01:00:00:16:3f:02:01:00:08:00 SRC=192.168.1.2 DST=192.168.1.1 LEN=64 TOS=0x00 PREC=0x00 TTL=64 ID=43324 DF PROTO=TCP SPT=520 DPT=32947 WINDOW=362 RES=0x00 ACK PSH URGP=0
Nov  3 11:18:28 dhcptest-primary kernel: IN= OUT=eth0 SRC=192.168.1.1 DST=192.168.1.2 LEN=64 TOS=0x00 PREC=0x00 TTL=64 ID=43974 DF PROTO=TCP SPT=32947 DPT=520 WINDOW=365 RES=0x00 ACK PSH URGP=0
Nov  3 11:18:28 dhcptest-primary kernel: IN=eth0 OUT= MAC=00:16:3e:02:01:00:00:16:3f:02:01:00:08:00 SRC=192.168.1.2 DST=192.168.1.1 LEN=64 TOS=0x00 PREC=0x00 TTL=64 ID=43325 DF PROTO=TCP SPT=520 DPT=32947 WINDOW=362 RES=0x00 ACK PSH URGP=0
Nov  3 11:18:28 dhcptest-primary kernel: IN= OUT=eth0 SRC=192.168.1.1 DST=192.168.1.2 LEN=64 TOS=0x00 PREC=0x00 TTL=64 ID=43975 DF PROTO=TCP SPT=32947 DPT=520 WINDOW=365 RES=0x00 ACK PSH URGP=0
Nov  3 11:18:28 dhcptest-primary kernel: IN=eth0 OUT= MAC=00:16:3e:02:01:00:00:16:3f:02:01:00:08:00 SRC=192.168.1.2 DST=192.168.1.1 LEN=64 TOS=0x00 PREC=0x00 TTL=64 ID=43326 DF PROTO=TCP SPT=520 DPT=32947 WINDOW=362 RES=0x00 ACK PSH URGP=0
Nov  3 11:18:29 dhcptest-primary kernel: IN= OUT=eth0 SRC=192.168.1.1 DST=192.168.1.2 LEN=64 TOS=0x00 PREC=0x00 TTL=64 ID=43976 DF PROTO=TCP SPT=32947 DPT=520 WINDOW=365 RES=0x00 ACK PSH URGP=0
Nov  3 11:18:29 dhcptest-primary kernel: IN=eth0 OUT= MAC=00:16:3e:02:01:00:00:16:3f:02:01:00:08:00 SRC=192.168.1.2 DST=192.168.1.1 LEN=64 TOS=0x00 PREC=0x00 TTL=64 ID=43327 DF PROTO=TCP SPT=520 DPT=32947 WINDOW=362 RES=0x00 ACK PSH URGP=0
Nov  3 11:18:31 dhcptest-primary kernel: IN= OUT=eth0 SRC=192.168.1.1 DST=192.168.1.2 LEN=64 TOS=0x00 PREC=0x00 TTL=64 ID=43977 DF PROTO=TCP SPT=32947 DPT=520 WINDOW=365 RES=0x00 ACK PSH URGP=0
Nov  3 11:18:31 dhcptest-primary kernel: IN=eth0 OUT= MAC=00:16:3e:02:01:00:00:16:3f:02:01:00:08:00 SRC=192.168.1.2 DST=192.168.1.1 LEN=64 TOS=0x00 PREC=0x00 TTL=64 ID=43328 DF PROTO=TCP SPT=520 DPT=32947 WINDOW=362 RES=0x00 ACK PSH URGP=0
Nov  3 11:18:34 dhcptest-primary kernel: IN= OUT=eth0 SRC=192.168.1.1 DST=192.168.1.2 LEN=64 TOS=0x00 PREC=0x00 TTL=64 ID=43978 DF PROTO=TCP SPT=32947 DPT=520 WINDOW=365 RES=0x00 ACK PSH URGP=0
Nov  3 11:18:34 dhcptest-primary kernel: IN=eth0 OUT= MAC=00:16:3e:02:01:00:00:16:3f:02:01:00:08:00 SRC=192.168.1.2 DST=192.168.1.1 LEN=64 TOS=0x00 PREC=0x00 TTL=64 ID=43329 DF PROTO=TCP SPT=520 DPT=32947 WINDOW=362 RES=0x00 ACK PSH URGP=0
Nov  3 11:18:38 dhcptest-primary kernel: IN= OUT=eth0 SRC=192.168.1.1 DST=192.168.1.2 LEN=76 TOS=0x00 PREC=0x00 TTL=64 ID=43979 DF PROTO=TCP SPT=32947 DPT=520 WINDOW=365 RES=0x00 ACK PSH URGP=0
Nov  3 11:18:40 dhcptest-primary kernel: IN= OUT=eth0 SRC=192.168.1.1 DST=192.168.1.2 LEN=76 TOS=0x00 PREC=0x00 TTL=64 ID=43980 DF PROTO=TCP SPT=32947 DPT=520 WINDOW=365 RES=0x00 ACK PSH URGP=0
Nov  3 11:18:41 dhcptest-primary kernel: IN=eth0 OUT= MAC=00:16:3e:02:01:00:00:16:3f:02:01:00:08:00 SRC=192.168.1.2 DST=192.168.1.1 LEN=64 TOS=0x00 PREC=0x00 TTL=64 ID=43330 DF PROTO=TCP SPT=520 DPT=32947 WINDOW=362 RES=0x00 ACK PSH URGP=0
Nov  3 11:18:48 dhcptest-primary kernel: IN=eth0 OUT= MAC=00:16:3e:02:01:00:00:16:3f:02:01:00:08:00 SRC=192.168.1.2 DST=192.168.1.1 LEN=64 TOS=0x00 PREC=0x00 TTL=64 ID=43331 DF PROTO=TCP SPT=520 DPT=32947 WINDOW=362 RES=0x00 ACK PSH FIN URGP=0
Nov  3 11:18:48 dhcptest-primary dhcpd: peer peer: disconnected
Nov  3 11:18:48 dhcptest-primary kernel: IN= OUT=eth0 SRC=192.168.1.1 DST=192.168.1.2 LEN=76 TOS=0x00 PREC=0x00 TTL=64 ID=43981 DF PROTO=TCP SPT=32947 DPT=520 WINDOW=365 RES=0x00 ACK PSH FIN URGP=0
Nov  3 11:18:48 dhcptest-primary dhcpd: failover peer peer: I move from normal to communications-interrupted
Nov  3 11:18:53 dhcptest-primary kernel: IN=eth0 OUT= MAC=00:16:3e:02:01:00:00:16:3f:02:01:00:08:00 SRC=192.168.1.2 DST=192.168.1.1 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=32541 DF PROTO=TCP SPT=49827 DPT=520 WINDOW=5840 RES=0x00 SYN URGP=0
Nov  3 11:18:53 dhcptest-primary kernel: IN= OUT=eth0 SRC=192.168.1.1 DST=192.168.1.2 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=4944 DF PROTO=TCP SPT=47069 DPT=520 WINDOW=5840 RES=0x00 SYN URGP=0
Nov  3 11:18:53 dhcptest-primary kernel: IN= OUT=eth0 SRC=192.168.1.1 DST=192.168.1.2 LEN=76 TOS=0x00 PREC=0x00 TTL=64 ID=43982 DF PROTO=TCP SPT=32947 DPT=520 WINDOW=365 RES=0x00 ACK PSH FIN URGP=0
Nov  3 11:18:54 dhcptest-primary kernel: IN=eth0 OUT= MAC=00:16:3e:02:01:00:00:16:3f:02:01:00:08:00 SRC=192.168.1.2 DST=192.168.1.1 LEN=64 TOS=0x00 PREC=0x00 TTL=64 ID=43332 DF PROTO=TCP SPT=520 DPT=32947 WINDOW=362 RES=0x00 ACK PSH URGP=0
Nov  3 11:18:56 dhcptest-primary kernel: IN=eth0 OUT= MAC=00:16:3e:02:01:00:00:16:3f:02:01:00:08:00 SRC=192.168.1.2 DST=192.168.1.1 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=32542 DF PROTO=TCP SPT=49827 DPT=520 WINDOW=5840 RES=0x00 SYN URGP=0
Nov  3 11:18:56 dhcptest-primary kernel: IN= OUT=eth0 SRC=192.168.1.1 DST=192.168.1.2 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=4945 DF PROTO=TCP SPT=47069 DPT=520 WINDOW=5840 RES=0x00 SYN URGP=0
Nov  3 11:19:02 dhcptest-primary kernel: IN=eth0 OUT= MAC=00:16:3e:02:01:00:00:16:3f:02:01:00:08:00 SRC=192.168.1.2 DST=192.168.1.1 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=32543 DF PROTO=TCP SPT=49827 DPT=520 WINDOW=5840 RES=0x00 SYN URGP=0
Nov  3 11:19:02 dhcptest-primary kernel: IN= OUT=eth0 SRC=192.168.1.1 DST=192.168.1.2 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=4946 DF PROTO=TCP SPT=47069 DPT=520 WINDOW=5840 RES=0x00 SYN URGP=0
Nov  3 11:19:14 dhcptest-primary kernel: IN=eth0 OUT= MAC=00:16:3e:02:01:00:00:16:3f:02:01:00:08:00 SRC=192.168.1.2 DST=192.168.1.1 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=32544 DF PROTO=TCP SPT=49827 DPT=520 WINDOW=5840 RES=0x00 SYN URGP=0
Nov  3 11:19:14 dhcptest-primary kernel: IN= OUT=eth0 SRC=192.168.1.1 DST=192.168.1.2 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=4947 DF PROTO=TCP SPT=47069 DPT=520 WINDOW=5840 RES=0x00 SYN URGP=0
Nov  3 11:19:20 dhcptest-primary kernel: IN= OUT=eth0 SRC=192.168.1.1 DST=192.168.1.2 LEN=76 TOS=0x00 PREC=0x00 TTL=64 ID=43983 DF PROTO=TCP SPT=32947 DPT=520 WINDOW=365 RES=0x00 ACK PSH FIN URGP=0
Nov  3 11:19:21 dhcptest-primary kernel: IN=eth0 OUT= MAC=00:16:3e:02:01:00:00:16:3f:02:01:00:08:00 SRC=192.168.1.2 DST=192.168.1.1 LEN=64 TOS=0x00 PREC=0x00 TTL=64 ID=43333 DF PROTO=TCP SPT=520 DPT=32947 WINDOW=362 RES=0x00 ACK PSH URGP=0
Nov  3 11:19:38 dhcptest-primary kernel: IN=eth0 OUT= MAC=00:16:3e:02:01:00:00:16:3f:02:01:00:08:00 SRC=192.168.1.2 DST=192.168.1.1 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=32545 DF PROTO=TCP SPT=49827 DPT=520 WINDOW=5840 RES=0x00 SYN URGP=0
Nov  3 11:19:38 dhcptest-primary kernel: IN= OUT=eth0 SRC=192.168.1.1 DST=192.168.1.2 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=4948 DF PROTO=TCP SPT=47069 DPT=520 WINDOW=5840 RES=0x00 SYN URGP=0
Nov  3 11:20:12 dhcptest-primary kernel: IN= OUT=eth0 SRC=192.168.1.1 DST=192.168.1.2 LEN=76 TOS=0x00 PREC=0x00 TTL=64 ID=43984 DF PROTO=TCP SPT=32947 DPT=520 WINDOW=365 RES=0x00 ACK PSH FIN URGP=0
Nov  3 11:20:26 dhcptest-primary kernel: IN=eth0 OUT= MAC=00:16:3e:02:01:00:00:16:3f:02:01:00:08:00 SRC=192.168.1.2 DST=192.168.1.1 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=32546 DF PROTO=TCP SPT=49827 DPT=520 WINDOW=5840 RES=0x00 SYN URGP=0
Nov  3 11:20:26 dhcptest-primary kernel: IN= OUT=eth0 SRC=192.168.1.1 DST=192.168.1.2 LEN=60 TOS=0x00 PREC=0x00 TTL=64 ID=4949 DF PROTO=TCP SPT=47069 DPT=520 WINDOW=5840 RES=0x00 SYN URGP=0


As seen in the log both servers stops sending packets after 118 seconds

After restoring communications I need to restart either of the servers to restore function.
#554150#10
Date:
2026-08-05 17:31:09 UTC
From:
To:
Dear submitter,

as the package isc-dhcp has just been removed from the Debian archive
unstable we hereby close the associated bug reports.  We are sorry
that we couldn't deal with your issue properly.

For details on the removal, please see https://bugs.debian.org/1143544

The version of this package that was in Debian prior to this removal
can still be found using https://snapshot.debian.org/.

Please note that the changes have been done on the master archive and
will not propagate to any mirrors until the next dinstall run at the
earliest.

This message was generated automatically; if you believe that there is
a problem with it please contact the archive administrators by mailing
ftpmaster@ftp-master.debian.org.

Debian distribution maintenance software
pp.
Thorsten Alteholz (the ftpmaster behind the curtain)