为什么ping会收到另一个ping命令数据包？

Question

I am learning about the ping implementation in C. The problem is, I was using a raw sockets to receive the packet. For all packets we have a identification value in ICMP header .

I was running the ping in multiple terminal.

For example, I was running three ping google.com in three terminals.

For the first ping the identification value is 23456, the second ping identification value is 34564, and the third ping identification value is 98763.

My problem is the second ping have to receives the identification with 34564 packet, but it receives the identification value as 23456.

For each ping the new raw socket is creating. But it receives another ping packet.

Can anyone please explain me, why it receives another ping packet ?

UPDATE:-

I have another one doubt. The doubt is,

raw sockets reads the packet from where and how it identify the packet is for this raw socket ?

UPDATE 1:-

Here is the link for the codes.

ping_common.c

ping.c

ping.h

Answer 1

What's you are seeing is by design of the raw socket, because raw sockets are meant to receive all the raw packets. So to only receive the reply to certain ICMP packets, you need to apply filters on the socket. First you can use ICMP_FILTER socket options to restrict receiving of certain ICMP types:

struct icmp_filter filter;
filter.data = <bit mask of ICMP types, like ICMP_REPLY>;
setsockopt(sock, SOL_RAW, ICMP_FILTER, &filter, sizeof filter)

Second, you can attach socket filter to enforce only receive the package with the given ICMP ID:

struct sock_fprog filter;
// set filter to check ID with your own ID
setsockopt(sock, SOL_SOCKET, SO_ATTACH_FILTER, &filter, sizeof filter);

Answer 2

To answer your other doubt:

• raw sockets reads the packet from where and how it identify the packet is for this raw socket ?

Raw socket sit along side other protocol handlers after IP layer. From book "Understanding Linux Network Internals" Chapter 25.5:

Here are some examples of interactions between protocols:

IP protocol

The ip_local_deliver_finish routine, described in Chapter 24, delivers ingress ICMP messages to the receive routine icmp_rcv registered by the ICMP protocol, but it also delivers them to the raw IP sockets that registered against the ICMP protocol (raw_v4_input).