diff --git a/xCAT/postscripts/configeth b/xCAT/postscripts/configeth
index 915d5e840..6e82999e3 100755
--- a/xCAT/postscripts/configeth
+++ b/xCAT/postscripts/configeth
@@ -428,7 +428,7 @@ elif [ "$1" = "-s" ];then
                     if [ ! -z "str_inst_ip" ];then
                         inst_ip_pre=`ip ro ls|grep -i ${str_inst_ip}|awk '{print $1}'|awk -F/ '{print $1}'`
                         if [ ! -z "inst_ip_pre" ];then
-                            str_inst_mask=`route |grep ${inst_ip_pre}|awk '{print $3}'|head -1`
+                            str_inst_mask=`route |grep ^${inst_ip_pre}|awk '{print $3}'|head -1`
                         fi
                     fi
                 fi
@@ -450,7 +450,7 @@ elif [ "$1" = "-s" ];then
                     if [ ! -z "str_inst_ip" ];then
                         inst_ip_pre=`ip ro ls|grep -i ${str_inst_ip}|awk '{print $1}'|awk -F/ '{print $1}'`
                         if [ ! -z "inst_ip_pre" ];then
-                            str_inst_mask=`route |grep ${inst_ip_pre}|awk '{print $3}'|head -1`
+                            str_inst_mask=`route |grep ^${inst_ip_pre}|awk '{print $3}'|head -1`
                         fi
                     fi
                 fi
@@ -473,7 +473,7 @@ elif [ "$1" = "-s" ];then
                     if [ ! -z "str_inst_ip" ];then
                         inst_ip_pre=`ip ro ls|grep -i ${str_inst_ip}|awk '{print $1}'|awk -F/ '{print $1}'`
                         if [ ! -z "inst_ip_pre" ];then
-                            str_inst_mask=`route |grep ${inst_ip_pre}|awk '{print $3}'|head -1`
+                            str_inst_mask=`route |grep ^${inst_ip_pre}|awk '{print $3}'|head -1`
                         fi
                     fi
                 fi