update readme for v6 inforeq

leshow · Aug 19, 2022 · 2255a03 · 2255a03
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diff --git a/README.md b/README.md
@@ -40,8 +40,8 @@ ex  dhcpv4:
         dhcpm 192.168.0.1 dora                  (unicast DORA to 192.168.0.1)
         dhcpm 192.168.0.1 dora -o 118,C0A80001  (unicast DORA, incl opt 118:192.168.0.1)
     dhcpv6:
-        dhcpm ::0 -p 9901 solicit       (unicast solicit to [::0]:9901)
-        dhcpm ff02::1:2 solicit         (multicast solicit to default port)
+        dhcpm ::0 -p 9901 inforeq       (unicast inforeq to [::0]:9901)
+        dhcpm ff02::1:2 inforeq         (multicast inforeq to default port)
 
 Positional Arguments:
   target            ip address to send to
@@ -54,9 +54,6 @@ Options:
   -t, --timeout     query timeout in seconds [default: 5]
   --output          select the log output format (json|pretty|debug) [default:
                     pretty]
-  --script          pass in a path to a rhai script
-                    (https://github.com/rhaiscript/rhai) NOTE: must compile
-                    dhcpm with `script` feature
   --no-retry        setting to "true" will prevent re-sending if we don't get a
                     response [default: false]
   --help            display usage information
@@ -68,7 +65,7 @@ Commands:
   inform            Send an INFORM msg
   decline           Send a DECLINE msg
   dora              Sends Discover then Request
-  solicit           Send a SOLICIT msg (dhcpv6)
+  inforeq           Send a INFORMATION-REQUEST msg (dhcpv6)
 ```
 
 ### Sending DHCP over arbitrary ports
@@ -125,6 +122,26 @@ Each sub-command (`discover`/`request`/`release`, etc) has sub-options. For exam
 dhcpm 255.255.255.255 discover --chaddr "80:FA:5B:41:10:6B"
 ```
 
+### dhcpv6
+
+With DHCPv6, many messages are sent on the multicast group `ff02::1:2` but responses are often unicast back on link-local addresses (starting with `fe80`). `dhcpm` won't be able to receive this data if you've got another dhcpv6 client listening on `[::0]:546`, the dhcpv6 client port. The other process is will likely read the datagram first.
+
+For example, my box has:
+
+```
+> sudo lsof -Pi UDP
+...
+NetworkMa     711            root   20u  IPv6 12173080      0t0  UDP leshowbox:546
+```
+
+Listening on this `[::0]:546`, so that process would need to be killed before `dhcpm` could print a reply. Still, I have often found it enough to use `dhpcm` to generate a message, then look at the response in wireshark or tcpdump to inspect its validity.
+
+Specify an interface with v6, it is necessary to join the multicast group.
+
+```
+> sudo dhcpm ff02::1:2 -i enp6s0 inforeq
+```
+
 ### Scripting
 
 Scripting support with [rhai](https://github.com/rhaiscript/rhai). Compile `dhcpm` with the `script` feature and give it a path with `--script`:

diff --git a/src/inforeq.rs b/src/inforeq.rs
@@ -5,7 +5,7 @@ use mac_address::MacAddress;
 use crate::opts::{self, parse_mac, v6::parse_params};
 
 #[derive(FromArgs, PartialEq, Eq, Debug, Clone)]
-/// Send a INFORMATION-REQUEST msg
+/// Send a INFORMATION-REQUEST msg (dhcpv6)
 #[argh(subcommand, name = "inforeq")]
 pub struct InformationReqArgs {
     /// supply a mac address for DHCPv6 (use "random" for a random mac) [default: first interface mac]

diff --git a/src/main.rs b/src/main.rs
@@ -46,6 +46,8 @@ use crate::{
     release::ReleaseArgs, request::RequestArgs, util::Msg,
 };
 
+const V6_MULTICAST: Ipv6Addr = Ipv6Addr::new(0xff02, 0, 0, 0, 0, 0, 1, 2);
+
 #[allow(clippy::collapsible_else_if)]
 fn main() -> Result<()> {
     let mut args: Args = argh::from_env();
@@ -119,9 +121,9 @@ fn main() -> Result<()> {
             socket
                 .bind_device(Some(int.name.as_bytes()))
                 .context("SO_BINDTODEVICE failed")?;
-            if bind_addr.is_ipv6() {
+            if bind_addr.is_ipv6() && bind_addr.ip() == V6_MULTICAST {
                 socket
-                    .join_multicast_v6(&"ff02::1:2".parse::<Ipv6Addr>().unwrap(), int.index)
+                    .join_multicast_v6(&V6_MULTICAST, int.index)
                     .context("join v6 multicast")?;
                 socket
                     .set_multicast_if_v6(int.index)
@@ -259,14 +261,14 @@ ex  dhcpv4:
         dhcpm 192.168.0.1 dora                  (unicast DORA to 192.168.0.1)
         dhcpm 192.168.0.1 dora -o 118,C0A80001  (unicast DORA, incl opt 118:192.168.0.1)
     dhcpv6:
-        dhcpm ::0 -p 9901 solicit       (unicast solicit to [::0]:9901)
-        dhcpm ff02::1:2 solicit         (multicast solicit to default port)
+        dhcpm ::0 -p 9901 inforeq       (unicast inforeq to [::0]:9901)
+        dhcpm ff02::1:2 inforeq         (multicast inforeq to default port)
         ")]
 pub struct Args {
     /// ip address to send to
     #[argh(positional)]
     pub target: IpAddr,
-    /// select a msg type (can't use solicit with v4, or discover with v6)
+    /// select a msg type (make sure msg type is consistent with ip type, i.e. v4 or v6)
     #[argh(subcommand)]
     pub msg: Option<MsgType>,
     /// address to bind to [default: INADDR_ANY:0]
@@ -321,7 +323,6 @@ pub enum MsgType {
     Inform(InformArgs),
     Decline(DeclineArgs),
     Dora(DoraArgs),
-    Solicit(SolicitArgs),
     InformationReq(InformationReqArgs),
 }
 
@@ -397,11 +398,6 @@ impl DoraArgs {
     }
 }
 
-#[derive(FromArgs, PartialEq, Eq, Debug, Clone, Copy)]
-/// Send a SOLICIT msg (dhcpv6)
-#[argh(subcommand, name = "solicit")]
-pub struct SolicitArgs {}
-
 pub mod util {
     use std::{fmt, time::Duration};