Articles tagged #parsing
Crafting ICMP-bearing IPv4 packets with the help of bitvec
So. Serializing IPv4 packets. Easy? Well, not exactly.
IPv4 was annoying to parse, because we had 3-bit integers, and 13-bit integers, and who knows what else. Serializing it is going to be exactly the same.
Right now, we don’t have a way to serialize that.
Let’s take the version and ihl fields, both of which are supposed
to take 4 bits, together making a byte. We could serialize them like this:
Crafting ARP packets to find a remote host's MAC address
Alright. ALRIGHT. I know, we’re all excited, but let’s think about what we’re doing again.
So we’ve managed to look at real network traffic and parse it completely. We’ve also taken some ICMP packets, parsed them, and then serialized them right back and we got the exact same result.
So I know what you’re thinking - let’s just move our way down the stack again - stuff that ICMP packet in an IP packet, then in an Ethernet frame, and then serialize the whole thing.
Parsing and serializing ICMP packets with cookie-factory.
In the last part, we’ve finally parsed some IPv4 packets. We even found a way to filter only IPv4 packets that contain ICMP packets.
There’s one thing we haven’t done though, and that’s verify their checksum. Folks could be sending us invalid IPv4 packets and we’d be parsing them like a fool!
This series is getting quite long, so let’s jump right into it.
Parsing IPv4 packets, including numbers smaller than bytes
Hello and welcome to Part 11 of this series, wherein we finally use some of the code I prototyped way back when I was planning this series.
Where are we standing?
Let’s review the progress we’ve made in the first 10 parts: first, we’ve started thinking about what it takes for computers to communicate. Then, we’ve followed a rough outline of the various standards and protocols that have emerged since the 1970s.
Consuming Ethernet frames with the nom crate
Now that we’ve found the best way to find the “default network interface”… what can we do with that interface?
Well, listen for network traffic of course!
use rawsock::open_best_library;
use std::time::Instant;
fn main() -> Result<(), Error> {
let lib = open_best_library()?;
let iface_name = format!(r#"\Device\NPF_{}"#, netinfo::default_nic_guid()?);
let iface = lib.open_interface(&iface_name)?;
println!("Listening for packets...");
// doing some low-cost logging over here
let start = Instant::now();
iface.loop_infinite_dyn(&mut |packet| {
println!(
"{:?} | received {} bytes",
start.elapsed(),
packet.len()
);
})?;
Ok(())
}
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