Routing_question

[Ibrahim Jamil]

Hi

when a server in the subnet 10.10.10.10/24  needs to talk to server 200.10.10.10 , first the server needs to contact his D/G 10.10.10.100 , in order to reach 200.10.10.10 (N:B the D.G has a static route to reach 200.10.10.10)  QUESTION does this server needs to contact his D/G each time needs to talk this server or some cache taken place , pls explain how?

thanks

jamil

[John Blakley]

Yes, it will go to the gateway everytime. That being said, there are things called "ip redirects" that if you have 2 routers on the same segment (read switch), and the default gateway is .1, but your other router is .2, if the route to 200.10.10.10 is pointing to router .2, then the default gateway can send a redirect to the host stating that "to get to 200.10.10.10, your better path is .2". Then the host can send directly to .2 everytime...

HTH,
John

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[Ibrahim Jamil]

Hi Jon

thanks for ur reply

Would you please explain more about the routing logic

thanks

ibrahim

[cadet alain]

Hi,

from a host perspective: i need to send an IP packet to a destination IP so

1° I do a logical bitwise AND between my IP address and my subnet mask

2° I do the same operation between the destination IP and my subnet mask

3° I compare both results: if equal then they are on same subnet and so I must arp for the destination MAC

    If non equal then they are on different networks and so I must arp for my default gateway MAC

4° before sending an arp request I look into my arp cache if it doesn't already exist and if not I send the request and cache the reply

5° I can then construct my frame and send it on the wire

6° if external IP the gateway will take care of the routing.

Regards.

Alain

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[Ibrahim Jamil]

thanks Alain