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ICND1 break down -- Pings and extended pings

The video talk about ping and extended ping:

The normal ping command (running under user EXEC mode),


allows us to trouble shooting routing problems.

On Cisco routers, we could get any of the following ping results:

  • !!!!! -- IP connectivity to destination exists.

  • ..... -- IP connectivity to destination doesn't exist.

  • U.U.U -- The local router has a route to the destination, but the downstream router doesn't have a route.

  • C.C.C -- congestion

  • ?.?.? -- unknown packet type

  • &.&.& -- packet lifetime exceeded
The extended ping command (running under privileged EXEC mode),

allows extended ping where you have more control.
Pressing Control + Shift +6 twice stops the pings.

When a normal ping command is sent from a router, the source address of the ping is the IP address of the interface that the packet uses to exit the router. If an extended ping command is used, the source IP address can be changed to any IP address on the router. The extended ping is used to perform a more advanced check of host reachability and network connectivity. In order to use this feature, enter ping at the command line and press Return. You are prompted for many advanced fields values such as Repeat count, Source address or interface, Set DF bit in IP header.

The usefulness of ping is magnified by command "debug ip packet".

When an IP address can be ping through, the "debug ip packet" results in the following output:

IP: s= (local), d= (Serial0), len 100, sending
IP: s= (Serial0), d= (Serial0), len 56, rcvd 3
IP: s= (Serial0), d= (Serial0), len 100, rcvd

When there's no entry in the routing table exists for a particular destination IP address, the packets aren't leaving the router, the "debug ip packet" will result in the output like the following:
IP: s= (local), d=, len 100, unroutable
IP: s= (local), d=, len 100, unroutable
IP: s= (local), d=, len 100, unroutable
IP: s= (local), d=, len 100, unroutable
IP: s= (local), d=, len 100, unroutable

The word unroutable indicates that no entry in the routing table exists for address in this case.

ICND1 and ICND2 break down

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