XPost: comp.os.linux.networking   
   From: grahn+nntp@snipabacken.se   
      
   On Sun, 2009-11-15, Rob Warnock wrote:   
   > glen herrmannsfeldt   wrote:   
   > +---------------   
   > | Rob Warnock  wrote:   
   > | > Beware that in some (most?) versions of Linux "ifconfig" will set the   
   > | > IP broadcast address *incorrectly* unless you specify it explicitly   
   > | > [thus causing various protocols that use IP broadcast for initial   
   > | > discovery to fail mysteriously!].   
   > |   
   > | I don't know what you mean by incorrect...   
   > +---------------   
   >   
   > I forget the exact scenario, but ISTR[1] if you did something like this:   
   >   
   >     ifconfig eth0 10.2.3.4 netmask 255.255.255.192   
   >   
   > then the broadcast address came up with 10.255.255.255, which is   
   > *definitely* the wrong value!! That is, it looked only at the   
   > Class A nature of 10.2.3.4 and ignored the netmask. This hit us hard   
   > since we were using network 10 (inside our firewall) and chopping it   
   > up into hundreds of tiny subnets (for separate test server groups),   
   > and if someone forgot to specify the broadcast address it messed up   
   > not only their system but potentially spammed the whole lab net. You   
   > had to be *very* careful to say, e.g.:   
   >   
   >     ifconfig eth0 10.2.3.4 netmask 255.255.255.192 broadcast 10.2.3.63   
      
   But this looks correct, doesn't it?   
      
     tuva:/home/grahn# ifconfig eth0:1 10.2.3.4 netmask 255.255.255.192   
     tuva:/home/grahn# ifconfig eth0:1   
     eth0:1    Link encap:Ethernet  HWaddr 00:0d:93:60:7e:78   
               inet addr:10.2.3.4  Bcast:10.2.3.63  Mask:255.255.255.192   
               UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1   
               Interrupt:41 Base address:0xa400   
      
     tuva:/home/grahn# ifconfig --version   
     net-tools 1.60   
     ifconfig 1.42 (2001-04-13)   
      
   > Not only that, but Linux's "ifconfig" didn't handle CIDR   
   > notation correctly, whereas in FreeBSD all you have to say is   
   > "ifconfig sis0 1.2.3.4/27" and *both* netmask & broadcast will   
   > be set correctly [to 255.255.255.224 and 1.2.3.31, respectively,   
   > in this example].   
      
   Can't see that bug either:   
      
     tuva:/home/grahn# ifconfig eth0:1 10.2.3.4/27   
     tuva:/home/grahn# ifconfig eth0:1   
     eth0:1    Link encap:Ethernet  HWaddr 00:0d:93:60:7e:78   
               inet addr:10.2.3.4  Bcast:10.2.3.31  Mask:255.255.255.224   
               UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1   
               Interrupt:41 Base address:0xa400   
      
   /Jorgen   
      
   --   
     // Jorgen Grahn    O  o   .   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)