I've setup a Lab with dnsmasq acting as DHCP Server, which I can use the
dhcp-reply-delay option to introduce a delay between the DHCPDISCOVER
and DHCPOFFER, as in the example below:
Mar 30 18:26:34 focal-dhcpsrv dnsmasq-dhcp[2470]: DHCPDISCOVER(ens3)
52:54:00:d7:10:13
Mar 30 18:26:34 focal-dhcpsrv dnsmasq-dhcp[2470]: 4195928115 reply delay: 3
Mar 30 18:26:37 focal-dhcpsrv dnsmasq-dhcp[2470]: DHCPOFFER(ens3)
192.168.150.119 52:54:00:d7:10:13
Just minor note that the delay only happens between DHCPDISCOVER and
DHCPOFFER, but not between DHCPREQUEST and DHCPACK:
Mar 30 18:22:13 focal-dhcpsrv dnsmasq-dhcp[2470]: DHCPREQUEST(ens3)
192.168.150.119 52:54:00:d7:10:13
Mar 30 18:22:13 focal-dhcpsrv dnsmasq-dhcp[2470]: DHCPACK(ens3) 192.168.150.119
52:54:00:d7:10:13 ubuntu
So, if this is a new interface (new mac) looking for an IP, the delay
will be added, but if this is an interface which was previously
configured and is asking to re-use the same IP (DHCPREQUEST), there
won't be any delays.
I believe this Lab will help reproducing the issue with and without the
proposed patch.
1. In a ideal scenario, where no delays were added (dhcp-reply-delay is
commented out), ipconfig will take approximately to do its job: it sends
a DHCPREQUEST, then DHCPDISCOVER and then another DHCPREQUEST in this
process:
- From the ipconfig perspective:
root@ubuntu:/etc/dhcp# date; /usr/lib/klibc/bin/ipconfig ens9; date
Wed Mar 30 19:25:44 UTC 2022
IP-Config: ens9 hardware address 52:54:00:f3:4e:0e mtu 1500 DHCP RARP
IP-Config: ens9 complete (dhcp from 192.168.150.2):
address: 192.168.150.105 broadcast: 192.168.150.255 netmask: 255.255.255.0
gateway: 192.168.150.1 dns0 : 192.168.150.2 dns1 : 0.0.0.0
domain : sts.lab
rootserver: 192.168.150.2 rootpath:
filename :
Wed Mar 30 19:25:54 UTC 2022
- From the dhcp server perspective:
Mar 30 19:25:45 focal-dhcpsrv dnsmasq-dhcp[2656]: DHCPREQUEST(ens3)
192.168.150.105 52:54:00:f3:4e:0e
Mar 30 19:25:45 focal-dhcpsrv dnsmasq-dhcp[2656]: DHCPACK(ens3) 192.168.150.105
52:54:00:f3:4e:0e ubuntu
Mar 30 19:25:54 focal-dhcpsrv dnsmasq-dhcp[2656]: DHCPDISCOVER(ens3)
52:54:00:f3:4e:0e
Mar 30 19:25:54 focal-dhcpsrv dnsmasq-dhcp[2656]: DHCPOFFER(ens3)
192.168.150.105 52:54:00:f3:4e:0e
Mar 30 19:25:54 focal-dhcpsrv dnsmasq-dhcp[2656]: DHCPREQUEST(ens3)
192.168.150.105 52:54:00:f3:4e:0e
Mar 30 19:25:54 focal-dhcpsrv dnsmasq-dhcp[2656]: DHCPACK(ens3) 192.168.150.105
52:54:00:f3:4e:0e
2. Adding a 5 seconds delay in dnsmasq (dhcp-reply-delay=5) and without
enforcing a timeout in ipconfig:
- From ipconfig perspective:
root@ubuntu:/etc/dhcp# date; /usr/lib/klibc/bin/ipconfig ens9; date
Wed Mar 30 19:34:09 UTC 2022
IP-Config: ens9 hardware address 52:54:00:f3:4e:0e mtu 1500 DHCP RARP
IP-Config: ens9 complete (dhcp from 192.168.150.2):
address: 192.168.150.105 broadcast: 192.168.150.255 netmask: 255.255.255.0
gateway: 192.168.150.1 dns0 : 192.168.150.2 dns1 : 0.0.0.0
domain : sts.lab
rootserver: 192.168.150.2 rootpath:
filename :
Wed Mar 30 19:34:27 UTC 2022
- From the dhcpserver perspective:
Mar 30 19:34:10 focal-dhcpsrv dnsmasq-dhcp[2773]: DHCPREQUEST(ens3)
192.168.150.105 52:54:00:f3:4e:0e
Mar 30 19:34:10 focal-dhcpsrv dnsmasq-dhcp[2773]: DHCPACK(ens3) 192.168.150.105
52:54:00:f3:4e:0e ubuntu
Mar 30 19:34:19 focal-dhcpsrv dnsmasq-dhcp[2773]: DHCPDISCOVER(ens3)
52:54:00:f3:4e:0e
Mar 30 19:34:19 focal-dhcpsrv dnsmasq-dhcp[2773]: 1004609631 reply delay: 5
Mar 30 19:34:24 focal-dhcpsrv dnsmasq-dhcp[2773]: DHCPOFFER(ens3)
192.168.150.105 52:54:00:f3:4e:0e
Mar 30 19:34:24 focal-dhcpsrv dnsmasq-dhcp[2773]: DHCPDISCOVER(ens3)
52:54:00:f3:4e:0e
Mar 30 19:34:24 focal-dhcpsrv dnsmasq-dhcp[2773]: 1004609631 reply delay: 5
Mar 30 19:34:26 focal-dhcpsrv dnsmasq-dhcp[2773]: DHCPOFFER(ens3)
192.168.150.105 52:54:00:f3:4e:0e
Mar 30 19:34:26 focal-dhcpsrv dnsmasq-dhcp[2773]: DHCPDISCOVER(ens3)
52:54:00:f3:4e:0e
Mar 30 19:34:26 focal-dhcpsrv dnsmasq-dhcp[2773]: 1004609631 reply delay: 5
Mar 30 19:34:28 focal-dhcpsrv dnsmasq-dhcp[2773]: DHCPOFFER(ens3)
192.168.150.105 52:54:00:f3:4e:0e
Mar 30 19:34:28 focal-dhcpsrv dnsmasq-dhcp[2773]: DHCPREQUEST(ens3)
192.168.150.105 52:54:00:f3:4e:0e
Mar 30 19:34:28 focal-dhcpsrv dnsmasq-dhcp[2773]: DHCPACK(ens3) 192.168.150.105
52:54:00:f3:4e:0e
Mar 30 19:34:28 focal-dhcpsrv dnsmasq-dhcp[2773]: DHCPREQUEST(ens3)
192.168.150.105 52:54:00:f3:4e:0e
Mar 30 19:34:28 focal-dhcpsrv dnsmasq-dhcp[2773]: DHCPACK(ens3) 192.168.150.105
52:54:00:f3:4e:0e
It takes 18 seconds for the process to complete, as dnsmasq adds 3x 5
seconds delay in the process
3. Using the -t to specify a 15 seconds timeout (when the actual process takes
18 seconds):
- From the ipconfig perspective:
root@ubuntu:/etc/dhcp# date; /usr/lib/klibc/bin/ipconfig -t 15 ens9; date
Wed Mar 30 19:37:11 UTC 2022
IP-Config: ens9 hardware address 52:54:00:f3:4e:0e mtu 1500 DHCP RARP
IP-Config: no response after 15 secs - giving up
Wed Mar 30 19:37:28 UTC 2022
(the timeout is properly enforced)
- From the dhcp server perspective:
Mar 30 19:37:12 focal-dhcpsrv dnsmasq-dhcp[2773]: DHCPREQUEST(ens3)
192.168.150.105 52:54:00:f3:4e:0e
Mar 30 19:37:12 focal-dhcpsrv dnsmasq-dhcp[2773]: DHCPACK(ens3) 192.168.150.105
52:54:00:f3:4e:0e ubuntu
Mar 30 19:37:21 focal-dhcpsrv dnsmasq-dhcp[2773]: DHCPDISCOVER(ens3)
52:54:00:f3:4e:0e
Mar 30 19:37:21 focal-dhcpsrv dnsmasq-dhcp[2773]: 2288189480 reply delay: 5
Mar 30 19:37:26 focal-dhcpsrv dnsmasq-dhcp[2773]: DHCPOFFER(ens3)
192.168.150.105 52:54:00:f3:4e:0e
Mar 30 19:37:26 focal-dhcpsrv dnsmasq-dhcp[2773]: DHCPDISCOVER(ens3)
52:54:00:f3:4e:0e
Mar 30 19:37:26 focal-dhcpsrv dnsmasq-dhcp[2773]: 2288189480 reply delay: 5
Mar 30 19:37:28 focal-dhcpsrv dnsmasq-dhcp[2773]: DHCPOFFER(ens3)
192.168.150.105 52:54:00:f3:4e:0e
Mar 30 19:37:28 focal-dhcpsrv dnsmasq-dhcp[2773]: DHCPDISCOVER(ens3)
52:54:00:f3:4e:0e
Mar 30 19:37:28 focal-dhcpsrv dnsmasq-dhcp[2773]: 2288189480 reply delay: 5
Mar 30 19:37:30 focal-dhcpsrv dnsmasq-dhcp[2773]: DHCPOFFER(ens3)
192.168.150.105 52:54:00:f3:4e:0e
Mar 30 19:37:30 focal-dhcpsrv dnsmasq-dhcp[2773]: DHCPREQUEST(ens3)
192.168.150.105 52:54:00:f3:4e:0e
Mar 30 19:37:30 focal-dhcpsrv dnsmasq-dhcp[2773]: DHCPACK(ens3) 192.168.150.105
52:54:00:f3:4e:0e
4. The problem only happens when the dhcp server is not listening / responding
on the network AND the interface is DOWN on the client, then the timeout gets
ignored:
root@ubuntu:/etc/dhcp# ip l set ens9 down
root@ubuntu:/etc/dhcp# date; /usr/lib/klibc/bin/ipconfig -t 2 ens9; date
Wed Mar 30 19:40:52 UTC 2022
IP-Config: ens9 hardware address 52:54:00:f3:4e:0e mtu 1500 DHCP RARP
IP-Config: no response after 2 secs - giving up
Wed Mar 30 19:41:02 UTC 2022
If the interface is up (and dhcp client not listening / responding) the
timeout is honored[-ish]:
3: ens9: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP
group default qlen 1000
link/ether 52:54:00:f3:4e:0e brd ff:ff:ff:ff:ff:ff
inet6 fe80::5054:ff:fef3:4e0e/64 scope link
valid_lft forever preferred_lft forever
root@ubuntu:/etc/dhcp# date; /usr/lib/klibc/bin/ipconfig -t 2 ens9; date
Wed Mar 30 19:42:00 UTC 2022
IP-Config: ens9 hardware address 52:54:00:f3:4e:0e mtu 1500 DHCP RARP
IP-Config: no response after 2 secs - giving up
Wed Mar 30 19:42:03 UTC 2022
Anyway, if someone can build a klibc-utils package for me with the proposed
patch, I can test the ipconfig behavior in this Lab.
For testing the boot time optimization, I believe I will need a linux-
oracle kernel built with the patch, since initramfs will get the
ipconfig binary from bin/ipconfig inside the initrd. If you can build
that, I can get access to an instance where I can validate the boot
optimization improvements.
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https://bugs.launchpad.net/bugs/1947099
Title:
ipconfig does not honour user-requested timeouts in some cases
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