[Dnsmasq-discuss] Incorrect broadcast address given

Simon Kelley simon at thekelleys.org.uk
Wed Oct 8 16:45:15 BST 2008


OB Lutz wrote:
> # ip addr show
> 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN
>     link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
>     inet 127.0.0.1/8 brd 127.255.255.255 scope host lo
> 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast
> state UP qlen 100
>     link/ether 00:d0:12:09:91:52 brd ff:ff:ff:ff:ff:ff
> 3: eth1: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast
> state DOWN qlen 100
>     link/ether 00:d0:12:19:91:52 brd ff:ff:ff:ff:ff:ff
> 4: br-lan: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue
> state UNKNOWN
>     link/ether 00:d0:12:09:91:52 brd ff:ff:ff:ff:ff:ff
>     inet 192.168.8.225/27 brd 192.168.8.255 scope global br-lan
> 5: wifi0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast
> state UNKNOWN qlen 1000
>     link/ieee802.11 00:15:6d:63:d4:31 brd ff:ff:ff:ff:ff:ff
> 6: ath0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast
> state UP qlen 1000
>     link/ether 00:15:6d:63:d4:31 brd ff:ff:ff:ff:ff:ff
>     inet 192.168.8.226/32 brd 255.255.255.255 scope global ath0
> 7: bmf0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc
> pfifo_fast state UNKNOWN qlen 500
>     link/[65534]
>     inet 192.168.8.226/32 brd 192.168.8.226 scope global bmf0
> 
> 

Looks like the duff broadcast address is being pulled from bmf0 because 
it has an address inside the range for br-lan

srk at ermintrude:~$ ipcalc 192.168.8.225/27
Address:   192.168.8.225        11000000.10101000.00001000.111 00001
Netmask:   255.255.255.224 = 27 11111111.11111111.11111111.111 00000
Wildcard:  0.0.0.31             00000000.00000000.00000000.000 11111
Network:   192.168.8.224/27     11000000.10101000.00001000.111 00000
HostMin:   192.168.8.225        11000000.10101000.00001000.111 00001
HostMax:   192.168.8.254        11000000.10101000.00001000.111 11110
Broadcast: 192.168.8.255        11000000.10101000.00001000.111 11111
Hosts/Net: 30                    Class C, Private Internet

That's why your second example works, since bmf0 is at 192.168.8.2.


The code in dnsmasq has an implicit assumption that the ip-ranges for 
all the interfaces are disjoint. It's probably possible to tweak this 
code, but the best course of action may be to use a different address 
for bmf0, if that's possible.


Cheers,

Simon.





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