CCNA Basics Part-2

How to assign an IP address to the Router and configure it?

Router(config)# interface ethernet 0 /0  or  serial 0/0
Router(config-if)ip address <IP address> <Subnet Mask>
Router(config-if)no shutdown

 We assign our default-gateway as the IP address to the ethernet port.

 When the router is switched ON, by default all the interfaces are administratively down. To make the interfaces up we give no shutdown command.

Why and where we use the clock rate?

The serial line has two ends DTE and DCE. This line goes up and down when IP address and no shutdown is configured on both sides and will be in asynchronous state always. To synchronize the link clock rate should be configured at DCE end.

How to find out the DCE end?

Router#sh controllers serial 0/0

Difference between Request timed out Destination host unreachable

Syntex of the command to be used:

Reply from <ip address> : <byte= > time<xms TTL=xxx

Request timed out

When the packet is lost in transition, we will get “request timed out” message.
Destination host unreachable

If the host doesn’t know the route to the destination - “Destination unreachable” message is displayed i.e., the specified address is not present in the routing table

Reply from <ip address> : <byte= > time <xms TTL=xxx
Reply from the destination indicates that the connection exists

Time To Live (TTL) – a field in an IP header that indicates the no. of routers (hops) the packet can cross. TTL for systems is 128 and for routers it is 255. If the destination is not reached before the TTL expires, then the packet is dropped. This stops IP packets from continuously circling around in the network looking for a home