Bug 142955

Summary: NetworkManager sets a default gateway although the dhcp server does not supply one.
Product: [openSUSE] SUSE Linux 10.1 Reporter: Forgotten User ZhJd0F0L3x <forgotten_ZhJd0F0L3x>
Component: NetworkAssignee: Robert Love <rml>
Status: RESOLVED WONTFIX QA Contact: E-mail List <qa-bugs>
Severity: Enhancement    
Priority: P5 - None    
Version: Alpha 4   
Target Milestone: ---   
Hardware: Other   
OS: Other   
Whiteboard:
Found By: Component Test Services Priority:
Business Priority: Blocker: ---
Marketing QA Status: --- IT Deployment: ---
Bug Depends on:    
Bug Blocks: 140732    
Attachments: /var/log/messages snippet with NM messages

Description Forgotten User ZhJd0F0L3x 2006-01-12 21:46:15 UTC 
I have a very small network here with one machine "server", running dnsmasq as a dhcp- and dns server.

I connected with NM via an unencrypted WLAN and got the following:
seife@strolchi:~> route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.100.0   *               255.255.255.0   U     0      0        0 air
loopback        *               255.0.0.0       U     0      0        0 lo
default         gost.nbg.s3e.de 0.0.0.0         UG    0      0        0 air

But the server does not provide a default gateway (gost.nbg.s3e.de is the server, 192.168.100.1)

this is the dnsmasq config (pretty basic, the dns information comes from /etc/hosts):
gost:~ # cat /etc/dnsmasq.conf
domain=nbg.s3e.de
dhcp-range=192.168.100.50,192.168.100.150,12h
dhcp-host=00:12:79:59:37:34,192.168.100.2
dhcp-host=00:0E:35:B0:C9:9E,192.168.100.3
# Set the "all subnets are local" flag
dhcp-option=3,

there are two MACs configured, one for LAN and one for WLAN.
I'll attach the log snippet from NetworkManager when connecting.
Comment 1 Forgotten User ZhJd0F0L3x 2006-01-12 21:52:24 UTC 
Created attachment 63190 [details]
/var/log/messages snippet with NM messages

i tried this multiple times, just to make sure that i did not make a mistake.
Comment 2 Forgotten User ZhJd0F0L3x 2006-01-12 21:57:53 UTC 
sorry, i forgot to set the assignee.
Comment 3 Robert Love 2006-01-12 22:08:13 UTC 
This is on purpose (so not a bug).

If a DHCP server does not send a "routers" field, NM will set the gateway to the DHCP server as a "last resort".

Is that actually a problem for you?
Comment 4 Forgotten User ZhJd0F0L3x 2006-01-12 22:32:53 UTC 
Hm, i actually deliberately set no gateway (because there is none :-), i believe it was to avoid long timeout. OTOH, gost.nbg.s3e.de should just return an "icmp destination unreachable" if it is "abused" as a router. Don't know ;-)
I will just have an eye on "unwanted side effects" and holler if i find one.

OTOH at home my dhcp server deliberately gives no gateway to prevent my kids machines to access the internet when booted into windows, (the linux setup has a static ip); so this might be a "lockdown setting" administrators might be interested in.

So this might be an enhancement, don't know.
Comment 5 Robert Love 2006-01-12 22:41:57 UTC 
The other side is that this is a deliberate feature: Some crappy home routers have  a bug where they do not set the "routers" field in the DHCP address (or they set some other non-standard field, forget).  So this is a cheap bit of logic that makes everything work for them.

I don't really see the downside.  If the machine is not a DHCP server, you aren't any worse off than not having a router.  A non-router should just reset the connection, so there is no timeout concern.  And it is only affecting non-local packets, anyhow.

I am inclined to not fix and close.
Comment 6 Robert Love 2006-01-13 20:04:10 UTC 
Marking WONTFIX.
Comment 7 Forgotten User ZhJd0F0L3x 2006-01-18 22:25:29 UTC 
i found a "use case".
Dial in via Modem. Default route points to the providers gateway.
Now i associate with my isolated WLAN.
Default route points to my dhcp server / access point.
Boom, internet is dead.

I admit this is a somewhat obscure usecase, but it happened to me some minutes ago when i changed from wired to wireles LAN in the local network :-)
Comment 8 Robert Love 2006-01-18 22:44:03 UTC 
I guess one would ask, why are you doing that?  ;-)

So I have another question:  Would you suggest "fixing" this, alleviating your problem, but at the expense of the broken routers and other beneficiaries of the "fallback" default gateway?
Comment 9 Forgotten User ZhJd0F0L3x 2006-01-18 23:32:02 UTC 
(In reply to comment #8)
> I guess one would ask, why are you doing that?  ;-)

Well, i am often already dialed in and the VPN is set up when i come home. This is what mobile connectivity is good for ;-)

> So I have another question:  Would you suggest "fixing" this, alleviating your
> problem, but at the expense of the broken routers and other beneficiaries of
> the "fallback" default gateway?

I'd appreciate a config option. But i'll accept this as LATER since there is more important stuff to fix right now.

Timo suggested an "intelligent" setting of the default route:
if there is already a default route and DHCP does not provide one, then do not set it.

This will get easier as soon as NM really starts managing dialup, then we can build a really intelligent solution.
Comment 10 Robert Love 2006-01-20 19:37:39 UTC 
Alright.  Let's revisit later.
Comment 11 Stephan Kulow 2008-06-25 09:34:40 UTC 
mass reopening all SuSE Linux bugs that are set to REMIND+LATER to change the resolution to WONTFIX (adapting to new policy)
Comment 12 Stephan Kulow 2008-06-25 09:36:45 UTC 
mass reopening all SuSE Linux bugs that are set to REMIND+LATER to change the resolution to WONTFIX (adapting to new policy)
Comment 13 Stephan Kulow 2008-06-25 09:41:48 UTC 
mass reopening all SuSE Linux bugs that are set to REMIND+LATER to change the resolution to WONTFIX (adapting to new policy)
Comment 14 Stephan Kulow 2008-06-25 09:53:15 UTC 
Closing old LATER+REMIND bugs as WONTFIX - if you still plan to work on it, feel free to reopen and set to ASSIGNED.

In case the report saw repeated reopen comments, it's due to bugzilla timing out on the huge request ;(