op-mode: T2874: Add new utill for mtu-check

1 files changed, 52 insertions, 0 deletions

diff --git a/src/op_mode/force_mtu_host.sh b/src/op_mode/force_mtu_host.sh
new file mode 100755
index 000000000..02955c729
--- /dev/null
+++ b/src/op_mode/force_mtu_host.sh
@@ -0,0 +1,52 @@
+#!/usr/bin/env bash
+#
+# Module: vyos-show-ram.sh
+# Displays memory usage information in minimalistic format
+#
+# Copyright (C) 2020 VyOS maintainers and contributors
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+target=$1
+interface=$2
+
+# IPv4 header 20 byte + TCP header 20 byte
+ipv4_overhead=40
+
+# IPv6 headter 40 byte + TCP header 20 byte
+ipv6_overhead=60
+
+# If no arguments
+if [[ $# -eq 0 ]] ; then
+    echo "Target host not defined"
+    exit 1
+fi
+
+# If one argument, it's ip address. If 2, the second arg "interface"
+if [[ $# -eq 1 ]] ; then
+    mtu=$(sudo nmap -T4 --script path-mtu -F $target | grep "PMTU" | awk {'print $NF'})
+elif [[ $# -eq 2 ]]; then
+    mtu=$(sudo nmap -T4 -e $interface --script path-mtu -F $target | grep "PMTU" | awk {'print $NF'})
+fi
+
+tcpv4_mss=$(($mtu-$ipv4_overhead))
+tcpv6_mss=$(($mtu-$ipv6_overhead))
+
+echo "
+Recommended maximum values (or less) for target $target:
+---
+MTU:     $mtu
+TCP-MSS: $tcpv4_mss
+TCP-MSS_IPv6: $tcpv6_mss
+"
+