[Bridge] Bridge interface not forwarding DHCP-Broadcast
Balaji J
ping2balaji at gmail.com
Tue Dec 13 18:15:52 UTC 2016
Thanks Stephen.
Can i attach an interface with IP assigned to it already/statically to a
bridge?
So if i understand correctly from your response, i should run dhcpclient on
br0 interface to assign IP for the same? and Lets say br0 gets an IP
assigned by DHCP-Server as "12.0.0.1".
Now my intention is to assign IP address to the Host(say host1) behind
Router-1 using the DHCP-Server running on/behind Router-2 as shown below:
Host1 <------> (eth2)[Router-1](eth1:100.1.1.1) <----------EoGRE
Tunnel----->(eth0:100.1.1.254)[Router-2](DHCP-Server)
So i thought Bridging eth2 to eth1 in Router-1 is the only way to achieve
the same as i want the dhcp-broadcast packet from Host-1 to get tunneled
over EogRE till Router-2. Is this assumption correct? or i am missing
something here?
Or i should not assign any IP to eth2 and instead do it in br0 in Router-1?
Any guidance would be very helpful and greatly appreciated.
Thanks,
...Balaji.J
On Tue, Dec 13, 2016 at 11:11 PM, Stephen Hemminger <
stephen at networkplumber.org> wrote:
> On Tue, 13 Dec 2016 21:13:43 +0530
> Balaji J <ping2balaji at gmail.com> wrote:
>
> > Hi all,
> >
> > I am trying to setup a bridge with 2 interfaces attached to it in
> Router-1.
> > Interface-1: eth1 ==> EoGRE Tunnel interface(gretap) connecting to
> another
> > Router-2 where DHCP server is running.
> > Interface-2: eth2 ==> Trying to use DHCP to assign IP for this eth2
> > interface from DHCP-Server running on Router-2.
> >
> > Basically the setup i am expecting is like:
> > (eth2)[Router-1](eth1:100.1.1.1) <----------EoGRE
> > Tunnel----->(eth0:100.1.1.254)[Router-2](DHCP-Server)
> >
> > Following are the setup i did to check the 1st stage to see if the
> > dhcp-discover broadcast is going out of Router-1 over EoGRE tunnel or
> not.
> > But i am not able to achieve the same.
> >
> > Can anyone please let me know what is missing here? Thanks in advance.
> >
> > Router-1:
> > 1) ip link add eogre type gretap local 100.1.1.1 remote 100.1.1.254 ==>
> > created gretap with endpoints.
> > 2) ip link set eogre up ==> brought the eogre interface up.
> > [root at centos]# ifconfig
> > eogre Link encap:Ethernet HWaddr 9E:25:FC:54:7F:F2
> > inet6 addr: fe80::9c25:fcff:fe54:7ff2/64 Scope:Link
> > UP BROADCAST RUNNING MULTICAST MTU:1462 Metric:1
> > RX packets:0 errors:0 dropped:0 overruns:0 frame:0
> > TX packets:6 errors:0 dropped:0 overruns:0 carrier:0
> > collisions:0 txqueuelen:1000
> > RX bytes:0 (0.0 b) TX bytes:492 (492.0 b)
> >
> > eth1 Link encap:Ethernet HWaddr 08:00:27:3C:FB:14
> > inet addr:100.1.1.1 Bcast:0.0.0.0 Mask:255.255.255.0
> > inet6 addr: fe80::a00:27ff:fe3c:fb14/64 Scope:Link
> > UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
> > RX packets:13 errors:0 dropped:0 overruns:0 frame:0
> > TX packets:40 errors:0 dropped:0 overruns:0 carrier:0
> > collisions:0 txqueuelen:1000
> > RX bytes:1398 (1.3 KiB) TX bytes:4103 (4.0 KiB)
> >
> > eth2 Link encap:Ethernet HWaddr 08:00:27:5E:7F:83
> > BROADCAST MULTICAST MTU:1500 Metric:1
> > RX packets:0 errors:0 dropped:0 overruns:0 frame:0
> > TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
> > collisions:0 txqueuelen:1000
> > RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
> > 3) brctl addbr br0 ==> created bridge interface
> > 4) brctl addif br0 eogre ==> attach eogre interface to bridge
> > 5) brctl addif br0 eth2 ==> attach eth2 interface to bridge
> > 6) sysctl -w net.ipv6.conf.eth2.disable_ipv6=1 ==> disable ipv6 in eth2
> > just to avoid unwanted ipv6 signalling messages from it.
> > 7) ifconfig eth2 up ==> eth2 iface up with no IP in it yet.
> > 8) ifconfig eogre up ==> eogre iface up
> > 9) ifconfig br0 up ==> Bridge up.
> > 10) brctl show ==>
> > bridge name bridge id STP enabled interfaces
> > br0 8000.0800275e7f83 no eogre
> >
> > eth2
> >
> > 11) brctl showstp br0
> >
> > [root at centos-dev ~]# brctl showstp br0
> > br0
> > bridge id 8000.0800275e7f83
> > designated root 8000.0800275e7f83
> > root port 0 path cost
> 0
> > max age 19.99 bridge max age
> > 19.99
> > hello time 1.99 bridge hello time
> > 1.99
> > forward delay 14.99 bridge forward delay
> > 14.99
> > ageing time 299.95
> > hello timer 0.50 tcn timer
> > 0.00
> > topology change timer 0.00 gc timer
> > 1.50
> > hash elasticity 4 hash max
> 512
> > mc last member count 2 mc init query count
> 2
> > mc router 1 mc snooping
> 1
> > mc last member timer 0.99 mc membership timer
> > 259.96
> > mc querier timer 254.96 mc query interval
> > 124.98
> > mc response interval 9.99 mc init query interval
> > 31.24
> > flags
> >
> >
> > eogre (0)
> > port id 0000 state
> > forwarding
> > designated root 8000.0800275e7f83 path cost
> 100
> > designated bridge 8000.0800275e7f83 message age timer
> > 0.00
> > designated port 8001 forward delay timer
> > 0.00
> > designated cost 0 hold timer
> > 0.00
> > mc router 1
> > flags
> >
> > eth2 (0)
> > port id 0000 state
> > forwarding
> > designated root 8000.0800275e7f83 path cost
> 4
> > designated bridge 8000.0800275e7f83 message age timer
> > 0.00
> > designated port 8002 forward delay timer
> > 0.00
> > designated cost 0 hold timer
> > 0.00
> > mc router 1
> > flags
> >
> > 12) dhclient -i eth2 ==> This command triggers a DHCP-DISCOVER
> > broadcast(both l2/l3 broadcast destination addressed) from eth2 and
> > initiate ip allocation process.
> >
> > Now if i capture packets in wireshark in eth1+br0+eogre interface of
> > Router-1, i don't see the dhcp-discover packet sent from eth2 interface
> > going over EoGRE Tunnel to Router-2.
> > But the same DHCP-Discover packet i can see if i capture in eth2
> > interface(obvious reason).
> >
> > Is it not like whatever packets coming in or originating from eth2 will
> be
> > bridged to eogre interface using bridge "br0"?
> > I am using kernel 2.6 in CentOS
> >
> > Can someone please help here?
> >
> > Regards,
> > ...Balaji
>
> You can't and shouldn't try to do anything that assigns an IP address
> to a device that is a member of a bridge. In your case that is eth2.
>
>
> The correct thing to do is run DHCP client on the bridge device.
>
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