Layer 3 Logic, with Hosts and Routers

Daughterofrnbsoul

Hey, when a host wants to send a Packet to a Destination IP that's not in it's Local Subnet, the Layer 3 Logic tells the host to send the Ip packet to a nearby Router in it's local Subnet Correct? How is that logic similar to routers ? The layer 3 logic for routers
tells the router to match The Destination IP with a Subnet ID and Mask in a routing table along with an outgoing interface or next hop ip. Do routers calculate layer 3 Logic for the Next Hop Ip also ? To determine if the Next-hop Ip is Reachable ?


Destination IP 192.168.1.1

ip route 192.168.1.0 255.255.255.0 10.1.1.2

C 10.1.1.0/24

dontstop

Daughterofrnbsoul wrote: »

The layer 3 logic for routers tells the router to match The Destination IP with a Subnet ID and Mask in a routing table along with an outgoing interface or next hop ip. Do routers calculate layer 3 Logic for the Next Hop Ip also ? To determine if the Next-hop Ip is Reachable ?


Destination IP 192.168.1.1

ip route 192.168.1.0 255.255.255.0 10.1.1.2

C 10.1.1.0/24

The router must have a route in it's table for the next hop 10.1.1.2 and the outgoing interface of that route must be up/up.

So let's say you've got a serial link between two routers (A & . If Router A's interface goes down, so does Router B's and the router takes the route out of the routing table. This will also cause any routes that rely on that next hop to also be removed. If the routers connect over an Ethernet LAN then it gets a little tricky. If A goes down, Router B's interface is still up and directly connected so the route will remain even though the next hop address is unreachable.

The second case is kind of like a host's default gateway being down. The host still has a connection to the Ethernet which is up, but the destination gateway is down. The host will just time out waiting for a reply.

Does this help?

Daughterofrnbsoul

dontstop wrote: »

The router must have a route in it's table for the next hop 10.1.1.2 and the outgoing interface of that route must be up/up.

So let's say you've got a serial link between two routers (A & . If Router A's interface goes down, so does Router B's and the router takes the route out of the routing table. This will also cause any routes that rely on that next hop to also be removed. If the routers connect over an Ethernet LAN then it gets a little tricky. If A goes down, Router B's interface is still up and directly connected so the route will remain even though the next hop address is unreachable.

The second case is kind of like a host's default gateway being down. The host still has a connection to the Ethernet which is up, but the destination gateway is down. The host will just time out waiting for a reply.

Does this help?

YesThankyu

rolando3321

In your Destination Mac - layer 2 - layer 3 thread I explained this in detail in my own words. Check it out if you have not already.