RE: 2NIC's on same network, possible?

Let's see...

-----Original Message-----
The default route is a fallback which applies to every address/network you do *not* have an explicit route for. I do not see how this would qualify as "two routes towards the same network".

Regards
Ansgar Wiechers

Dig into tcp/ip and Ethernet (the 802.3 standards stuff - start at http://grouper.ieee.org/groups/802/3/)

There's nothing that prohibits multiple routes with equal metrics.

The entire concept of 'one' route is fiction, imposed by the OS, because people like deterministic systems. In reality, it's entirely up to the router to decide. Factors invisible to the outside/end user are valid. So are random choice, load-balancing, sheer cussedness - anything you can thing of is valid. The only thing required is that a router forward the packet or reject it. Dropping packets without notice (ACK/NACK or flow control) is bad, but the various protocols will even recover from that.

-----Burton

-----Original Message-----
a.b.c.d/e is a "new" notation ("CIDR") used to identify a netblock. It identifies a network beginning at a.b.c.d where e bytes are the network portion. There's an RFC that covers this in depth, but the old-style A,B,C networks are /8, /16, /24 respectively. A slight overapproximation of the maximum number of hosts on a /e network is 2**(31-e). An IP address is 32 bits, e of which identify the network. So, 32-e of them identify the host. There are 2**n possible ways to set n bits (and the maximum value of n bits is 2**(n-1)).

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Probably the other post was right and your friend has used a netmask appropriate for a /e network.

Justin

The CIDR RFCs are:

    RFC 1517: Applicability Statement for the Implementation of CIDR
    RFC 1518: An Architecture for IP Address Allocation with CIDR
    RFC 1519: CIDR: An Address Assignment and Aggregation Strategy
    RFC 1520: Exchanging Routing Information Across Provider Boundaries in

The actual number of hosts on a /e network is 2**(32-e) - 2

The -2 covers the all zeros and all ones host portions, used for broadcasts. (Technically the all zero is probably a legal address but historically some vendors (Sun) used it for broadcasts so it's best to stay away).

8<=e<=31 (Because the largest blocks assigned are /8s and the smallest normally usable is /30 - a /31 has only the two broadcast addresses --- still, this can be useful for unnumbered point-to-point links)

Some example values:

/e Host bits # usable hosts

---- --------- --------------
/31 1 0
/30 2 4
/29 3 6
/28 4 14
/27 5 30
/26 6 62
/25 7 126
/24 8 254
/23 9 510
/16 16 65534
/8 24 16777214

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See the "IP Subnetting HowTo" - see

http://www.ibiblio.org/pub/Linux/docs/HOWTO/other-formats/html_single/IP-Sub
networking.html. For other formats, start your search here:
http://www.tldp.org/.

-----Burton