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TOPIC: Routing & ACL question

Re: Routing & ACL question 8 years 4 months ago #36270

  • apit
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Now lets take this logic and apply it to our current situation. If you a host pc on the router 1 attached network 196.186.0.0/24 with an ip address of 196.186.0.5 and you want to contact(ping) the address 196.136.0.6 on the router 2 attached network of 196.186.0.0/24 what will happen when host 1 tries to transmit a ping to 196.186.0.5/24?


Do you mean a host at network 2 connected to router 1 via Gi 0/1 using ip 192.168.0.5 try to ping to a host at network 2 connected to router 2 via Gi 0/1 using ip 192.168.0.6 ?



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If refer to the above diagram, host 192.168.0.5 will :

1- Compare source ip(192.168.0.5) & subnetmask(255.255.255.0) with destination ip(192.168.0.6) & subnetmask(255.255.255.0). In that case, source & destination is the same.

2- Check destination Mac address (192.168.0.6) exist or not in router 1. Try issue "sh ip arp". No Mac address (192.168.0.6) found.

3- Send ARP request for 192.168.0.6 (from router 1 to router 2)

4- create frame with source 7 destination host MAC.

5- Ping return success

Re: Routing & ACL question 8 years 4 months ago #36272

  • Nevins
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1- Compare source ip(192.168.0.5) & subnetmask(255.255.255.0) with destination ip(192.168.0.6) & subnetmask(255.255.255.0). In that case, source & destination is the same.


Your partially correct. Lets work though using our logic table.




The statment:

Compare source ip(192.168.0.5) & subnetmask(255.255.255.0) with destination ip(192.168.0.6) & subnetmask(255.255.255.0). In that case, source & destination is the SAME.


Is roughly equivalent to the logic statement :

IF HOST IP && HOST SUBNET MASK = DESTINATION IP && DESTINATION SUBNETMASK which in the current situation equates to the TRUE leg of the logic.



So the next thing we must look at is if the destination mac address would exist in host 192.168.0.5's mac address table. Would it exist in the mac address table? Does host 192.168.0.5 have 192.168.0.6's mac address in it's table?
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Re: Routing & ACL question 8 years 4 months ago #36303

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So the next thing we must look at is if the destination mac address would exist in host 192.168.0.5's mac address table. Would it exist in the mac address table? Does host 192.168.0.5 have 192.168.0.6's mac address in it's table?


oh i see...we have to check the destination MAC 192.168.0.6 in host 192.168.0.5 MAC address table...i though that we have to check the destination MAC in router 1 by issue command "show ip arp"...

To check MAC address table in host 192.168.0.5, just issue command "arp -a"...so the result no MAC address for host 192.168.0.6 found in MAC Address table host 192.168.0.5

Re: Routing & ACL question 8 years 4 months ago #36310

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Okay so the computer puts out an arp request to everyone on the Lan segment:

Essentially the arp request is asking does anyone have the Mac address for 192.168.0.6 ?


So does anyone reply with the mac address for 192.168.0.6?
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Re: Routing & ACL question 8 years 4 months ago #36314

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Essentially the arp request is asking does anyone have the Mac address for 192.168.0.6 ?
So does anyone reply with the mac address for 192.168.0.6?


Anyone in this scenario is a switch or router?

Both switch & router 1 do not reply the 192.168.0.6 MAc Address.

Re: Routing & ACL question 8 years 4 months ago #36315

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There is only one rule in replying to arp packets. The rule is "if you are the destination reply".

So in this example would 196.168.0.6 be able to reply to the arp request?

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