Allow free selection of MTU by the user

Various ISPs (or equipment?) seem to hand out an MTU of only 576 bytes.
Hwoever, this does not seem to be intentional which is why we would like
to manually overwrite this in the configuration.

dhcpcd only allows setting a maximum MTU of 1472 bytes which does not
seem to have any rationale (any more). Although Ethernet might limit any
MTU to less, IPv6 and IPv4 support MTUs of up to 64KiB.

This patch allows the user to configure the MTU freely with providing
some sanity check.

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>

diff --git a/src/dhcp-common.h b/src/dhcp-common.h
index a82fcd4cec8e77aea45a9e8bd25a54dfbbe6692f..d66208228a9406859dc13e46285c7380aca6e3c7 100644 (file)
--- a/src/dhcp-common.h
+++ b/src/dhcp-common.h
@@ -46,10 +46,11 @@
 #define NS_MAXLABEL MAXLABEL
 #endif
 
-/* Max MTU - defines dhcp option length */
-#define        IP_UDP_SIZE               28
-#define        MTU_MAX                 1500 - IP_UDP_SIZE
-#define        MTU_MIN                  576 + IP_UDP_SIZE
+/* Max/Min MTU */
+#define        MTU_MAX                 65536
+#define        MTU_MIN                   576
+
+#define        IP_UDP_SIZE                28
 
 #define        OT_REQUEST              (1 << 0)
 #define        OT_UINT8                (1 << 1)