Re: Should ipaliased IP addresses answer broadcast packets?

From: Pekka Savola (pekkas@netcore.fi)
Date: Sun Jan 20 2002 - 08:30:49 EST


On Sun, 20 Jan 2002, Rob Fulton wrote:
> The game client has however been unable to connect to the server, using
> tcpdump I can see the request from the server going to the broadcast address
> as shown below.
>
> 11:53:01.315928 kryten.1480 > 255.255.255.255.27015: udp 16
>
> The server however, never replies. When pinging the broadcast address, the
> ip address of the interface replies as shown below but none of the aliased
> addresses reply to the broadcast ping. Is this normal behaviour? Should
> aliased addresss reply to pings?
>
> 64 bytes from 192.168.0.101: icmp_seq=2 ttl=255 time=0.0 ms

When pinging 255.255.255.255 the main IP address should answer. This is
the same as when pinging 192.168.0.255. Check your firewalling rulesets,
perhaps?

IP aliases in BSD are defined as follows:

 - a.b.c.d/255.255.255.255 if there is one "main" address in the same
network (which will respond to broadcasts)
 - a.b.c.d/255.255.255.0 (or something else) if there are no other
addresses in the same network

In Linux, all aliases can be defined as below and they "just work".

-- 
Pekka Savola                 "Tell me of difficulties surmounted,
Netcore Oy                   not those you stumble over and fall"
Systems. Networks. Security.  -- Robert Jordan: A Crown of Swords

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