On Thu, Jun 30, 2005 at 12:06:11PM +0200, Ivo Vachkov wrote:

> Next problem: How to represent many, many different combinations of
> routing rules in a common manner ???
> And the answer - HASHING !!! :)
> 
> Using the route command before kernel gets following info:
> - dst - 192.168.0.0/24
> - src - 192.168.1.0/24
> - TOS - any
> - L4 Proto - TCP (6)
> - Length - any
> 
> Now we use some hash function over all these values and get unique
> value for that routing entry that corresponds to gateway 172.16.0.1.
> We use this pair (hash value <-> gateway address) as key <-> value in
> RADIX or AVL tree.
> 
> On each outgoing packet we calculate it's hash over the IP Header
> fields, search that value in the table (tree) and route it over the

How? The hashes from the packet won't match the hashes in the table.
Because in the table, there would be addrsss/mask entries which are not
identical to the actual values in the packets.

Also, if you embed all the criteria in one routing table, how will you
learn dynamic routing daemons (ospfd et al.) to add the
source/protocol/TOS fields you need to the transient entries that they
create in the FIB? Because now routing daemons know only about the
dest-address criterion.

As the daemons (at least zebra/quagga) are modeled according to Cisco, it
would be interesting to know how Cisco does it.

Bye	Pavel