ubuntu 15.04 dhcp: option routers and option rfc3442-classless-static-routes

[Nastya]

Hi.
Sorry for my bad english.
Iam using option rfc3442-classless-static-routes in my dhcp-server.

# cat /var/lib/dhcp/dhclient.eth0.leases
lease {
  interface "eth0";
  fixed-address 192.168.120.170;
  option subnet-mask 255.255.255.0;
  option routers 192.168.120.1;
  option dhcp-lease-time 86400;
  option dhcp-message-type 5;
  option domain-name-servers 192.168.120.1;
  option dhcp-server-identifier 192.168.120.1;
  option ntp-servers 192.168.120.1;
  option rfc3442-classless-static-routes 24,10,125,0,192,168,120,110;
  option broadcast-address 192.168.120.255;
  option domain-name "home.xmu";
  renew 1 2015/06/15 05:45:48;
  rebind 1 2015/06/15 17:04:48;
  expire 1 2015/06/15 20:04:48;
}

In other operation system:
# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.120.1 0.0.0.0 UG 0 0 0 eth0
10.125.0.0 192.168.120.110 255.255.255.0 UG 0 0 0 eth0
192.168.120.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0

In ubuntu 15.04:
# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
10.125.0.0 192.168.120.110 255.255.255.0 UG 0 0 0 eth0
192.168.120.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0

No default gateway!!!

# cat /var/lib/dhcp/dhclient.leases
lease {
  interface "eth0";
  fixed-address 192.168.120.169;
  option subnet-mask 255.255.255.0;
  option routers 192.168.120.1;
  option dhcp-lease-time 86400;
  option dhcp-message-type 5;
  option domain-name-servers 192.168.120.1;
  option dhcp-server-identifier 192.168.120.1;
  option ntp-servers 192.168.120.1;
  option rfc3442-classless-static-routes 24,10,125,0,192,168,120,110;
  option broadcast-address 192.168.120.255;
  option domain-name "home.xmu";
  renew 1 2015/06/15 07:41:11;
  rebind 1 2015/06/15 16:57:38;
  expire 1 2015/06/15 19:57:38;
}

If i comment option rfc3442-classless-static-routes in my dhcp-server.
Default gateway works fine:
# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.120.1 0.0.0.0 UG 0 0 0 eth0
192.168.120.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0

# cat /etc/issue
Ubuntu 15.04 \n \l

# uname -a
Linux wp01 3.19.0-20-generic #20-Ubuntu SMP Fri May 29 10:10:47 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

# aptitude show isc-dhcp-client
Package: isc-dhcp-client
State: installed
Automatically installed: no
Version: 4.3.1-5ubuntu2.2
Priority: important
Section: net
Maintainer: Ubuntu Developers <email address hidden>
Architecture: amd64
Uncompressed Size: 698 k
Depends: libc6 (>= 2.15), libdns-export100, libirs-export91, libisc-export95, debianutils (>= 2.8.2), isc-dhcp-common (= 4.3.1-5ubuntu2.2), iproute2
Suggests: resolvconf, avahi-autoipd, apparmor
Provides: dhcp-client

# aptitude show isc-dhcp-common
Package: isc-dhcp-common
State: installed
Automatically installed: no
Version: 4.3.1-5ubuntu2.2
Priority: important
Section: net
Maintainer: Ubuntu Developers <email address hidden>
Architecture: amd64

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Alejandro Mery (amery)]

this bug is horrible. on environments where DHCP is served by a windows server there is no way of passing the default gateway via static routes ("rfc3442-classless-static-routes"). it's MS fault, but the client should be tolerant and notice rfc3442-classless-static-routes doesn't include a default gateway and use "routes" to fill the gap.

[renard (renard0)]

I can confirm I hit the same bug in a full Linux environment.
- server: 4.2.4-7ubuntu12.3
- client: 4.3.1-5ubuntu4

All clients (+500 hosts) in 4.2.4-7ubuntu12.3 work like a charm.

I cannot understand why this had changed. Any planned date to resolve this issue?

Thanks.

[Matthieu Herrb (matthieu-herrb)]

In fact its not a bug.
The RFC3442 explicitely says that clients that use the classless-static-route option (121) MUST ignore any router specified in the routers (default gateway) option. (page 5, DHCP Client Behavior)

[Alexey Lyashkov (alexey.lyashkov)]

In fact, RedHat, Windows, MacOS don't ignore an default routes with classless-static_route option.
What about to add an some tunable to have same behavior in Ubuntu? It should be not a hard