nyetworking in 2.4

Mark Hummel mhummel at pcug.org.au
Sun Aug 26 16:54:06 EST 2001

I obviously don't understand networking. According to the doco all I have
to do is such and such, (two lines) and it'll work. Well, it was working

What am I trying to do? At the very least, I want two machines to be able
to ping each other, across a hub or a switch. 

After doing:
ifconfig eth0 netmask up, 

one machine (call it A) can't see the switch (address

the routing table shows:
Destination     Gateway         Genmask         Flags Metric Ref   Use Iface     *        U     0      0     0 eth0

I just want to reiterate my understanding of how routing works, in case
I've misunderstood something. Assume the routing table is represented by
the output of the route command as above. 

Then, to connect to a machine with IP address, the following
1. The destination address is ANDed with the network mask & =

2. This value is compared top down with all entries. In this case, there
is a match. This means that the packet will be sent down interface eth0. 

3. Because ethernet is a broadcast medium, all packets can be seen on the
network, but only the destination should pay any attention to the packet. 
Now surely, all nodes are on the same class C network?

Checking the output from tcpdump yields: 
16:47:52.672874 arp who-has tell

with ARP set in ifconfig, and with  NOARP set: (ICMP request) > 

The situation regarding blinking lights:
1. The activity light on the switch and hub blink furiously when there is
one entry in the routing table
2. The lights are more sedate with more entries. I don't know if this is 

A question: 
Does the order in which the routing table is set up matter?

Finally, (thankyou for your patience) I did once find the magic
incantation to get this all working but I obviously don't know what, 
and further don't even understand why..



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