[network] [PATCH 3/4] util: add function mtu_is_valid

[Jonatan Schlag <jonatan.schlag@ipfire.org>]

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This function checks if an mtu is valid for a given IP protocol.

Signed-off-by: Jonatan Schlag <jonatan.schlag(a)ipfire.org>
---
 src/functions/functions.util | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/src/functions/functions.util b/src/functions/functions.util
index 4b6f956..98ad9d4 100644
--- a/src/functions/functions.util
+++ b/src/functions/functions.util
@@ -321,6 +321,25 @@ isipaddress() {
 	ip_is_valid ${addr}
 }
 
+mtu_is_valid() {
+
+local proto=${1}
+local mtu=${2}
+
+case ${proto} in
+	ipv4)
+		[ ${mtu} -ge 576 ] && [ ${mtu} -le 9000 ]
+		;;
+	ipv6)
+		[ ${mtu} -ge 1280 ] && [ ${mtu} -le 9000 ]
+		;;
+	*)
+		error "${proto} is not a valid proto"
+		return ${EXIT_ERROR}
+		;;
+esac
+}
+
 backtrace() {
 	local start=1
 
-- 
2.6.3