Routing & ACL question

zoom in from router HQ to router branch physical connecti0n ::

My current connection is using ethernet port (fa 0/0/0) from router and then connected to the ISP layer 2 switch..

Both ISP layer 2 switch HQ and branch physically connected through SMF fiber optic.

refer to the diagram..

fa 0/0/0 at both router using the same subnetmask and ip range....and they can PING each other without any problem compare to Gi 0/0 and Gi 0/1..

maybe this is because the fa 0/0/0 is connected to ISP layer 2 switch.. is it right?

Of course F0/0/0 on router 1 can ping F0/0/0 on router 2 they are directly connected. For directly connected devices to be able to ping eachother the only requirement is that they use the correct encapsulation, have proper clock speed enabled and not be shut down.

F0/0/0 on router 1 to GI0/1 on router 2 on the other hand requires routing.


So if router 1 is trying to ping interface GI0/1 on router 2. It has to make a routing determination on where to send the packet beyond it's directly connected interface.

Do a show IP route for R1 and we'll do another breakdown of logic.

Of course F0/0/0 on router 1 can ping F0/0/0 on router 2 they are directly connected.

that mean , only direct physical cable connected each other can use the same ip range & subnetmask..Is it?

For directly connected devices to be able to ping eachother the only requirement is that they use the correct encapsulation, have proper clock speed enabled and not be shut down.

For encapsulation & clock speed, this is refering to serial connection is it? My current connection is using ethernet port (fa 0/0/0) from router and then connected to the ISP layer 2 switch..

Both ISP layer 2 switch HQ and branch physically connected through SMF fiber optic.

So in my environment , they are no requirement to configure encapsulation & clock speed...Is it?

F0/0/0 on router 1 to GI0/1 on router 2 on the other hand requires routing.

oh i see...before this i thought that Gi 0/0 or Gi 0/1 on R1 can PING directly to Gi 0/0 or Gi 0/1 on R2 using same subnet & ip range because they sit in the same router...

So if router 1 is trying to ping interface GI0/1 on router 2. It has to make a routing determination on where to send the packet beyond it's directly connected interface.

Router 1 is referring to Fa 0/0/0 is it?

How to do the routing determination ? Is it by checking router 1 routing table?

Now i can see that we start from layer 1 which is cabling infrastructure and then goes to Layer 2 which is MAC address determination and now goes to layer 3 which is routing determination..

Do a show IP route for R1 and we'll do another breakdown of logic.

Ok...i will paste it ASAP..

Nevins wrote:
Of course F0/0/0 on router 1 can ping F0/0/0 on router 2 they are directly connected.

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that mean , only direct physical cable connected each other can use the same ip range & subnetmask..Is it?

It means because the link is up and the cable is a direct connection that routers on both sides are going to be able to ping the other end. It does not however mean that because you can ping that interface you can ping any other on a connected router because the router has no logical reason to know what else is beyond that link. The subnet id and subnet are already known for directly connected links and added to the routing table as soon as a link becomes active. To an extent this is still a routing choice but there is no real question that it will appear in the routing table.

Nevins wrote:
For directly connected devices to be able to ping eachother the only requirement is that they use the correct encapsulation, have proper clock speed enabled and not be shut down.

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For encapsulation & clock speed, this is refering to serial connection is it? My current connection is using ethernet port (fa 0/0/0) from router and then connected to the ISP layer 2 switch..

Both ISP layer 2 switch HQ and branch physically connected through SMF fiber optic.

So in my environment , they are no requirement to configure encapsulation & clock speed...Is it?

You are correct. encapsulation and clock speed are requirements of a serial connection. I guess I should have said the only possible requirements for directly connected devices to ping one another is to use the correct encapsulation have proper clock speed enabled and not be shut down.

Quote:

So if router 1 is trying to ping interface GI0/1 on router 2. It has to make a routing determination on where to send the packet beyond it's directly connected interface.

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Router 1 is referring to Fa 0/0/0 is it?

How to do the routing determination ? Is it by checking router 1 routing table?

Router 1 actually in this case refers to router 1.

The routing determination is done by examining a routing table.


In any case bust out the routing tables for the 2 routers and we'll see what choices the routers can make.