ICMP Messages doubt ?

Question

Please explain these points :

No ICMP error message will be generated for a fragmented datagram that is not the first fragment .

No ICMP error message will be generated for a datagram having a multicast address .

No ICMP error message will be generated for a datagram having a special address such as 127.0.0.0

Comments

ICMP error messages are generated when router or destination host encounters any problem while processing packets : 

Now we know that all 1s in the IP address is used for multicasting and it is not applicable for network layer. But even if a datagram contains such an address, no ICMP error messages would be generated. 

127.0.0.0 is a special IP address which is used for loopback testing . But even if a datagram contains such an address, no ICMP error messages would be generated. 

The points which you have mentioned above are some exceptional cases in which ICMP error messages will not be generated. 

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ICMP actually creates PING, which looks, if destination reachable or not

Destination-unreachable messages with codes 2 or 3 can be created only by the destination host.Other destination-unreachable messages can be created only by routers.

 

 point 1: I think only first fragment needed destination address

point 2: broadcast address need router , multicast address does need destination address or router

point 3: loopback address also no need of router , and it's destination and source address is same. So, no need ICMP  packet

https://www.coursehero.com/file/pr3486/No-ICMP-error-message-will-be-generated-for-a-fragmented-datagram-that-is-not/

ok?

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@srestha

mam, questioner need explanation(reason), behind those points.

moreover, PING uses ICMP but not ICMP uses PING

 

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@Sayan , can u plz explain how all 1's is not applicable to network layer ? If it has all 1's then it would be a directed broadcast address so it will be sent to all the hosts within that network , where's the issue ?

 

Now we know that all 1s in the IP address is used for multicasting andit is not applicable for network layer. But even if a datagram contains such an address, no ICMP error messages would be generated.

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@shaik , If PING uses ICMP then why we say loopback testing doesn't require ICMP packet ?

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@radha gogia

loop back testing uses ICMP packets but if that packet lost , further ICMP error Packet doesn't generated.

 

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What is reason for No ICMP error message will be generated for a fragmented datagram that is not the first fragment .

@radha gogia @Shaik Masthan @Bikram

Answer 1

specifications set for ICMP RFC 792 states that ICMP error messages should not be generated when their usage will generate an excessive amount of network traffic. For example, RFC 1122 states that ICMP error messages should not be sent as the result of receiving:

• Another ICMP error message (although ICMP error messages can be sent in response to ICMP query messages)

• An IGMP message of any kind

• An IP datagram with a destination IP address for a broadcast or multicast address

• An IP datagram with a nonspecific source address (all zeroes, a loopback address, or a broadcast or multicast address)

• A data-link frame with a broadcast or multicast address

• Any fragment—other than the first fragment—from a fragmented IP datagram