When working with RHEL or other Linux distributions, you don't always have the luxury of installing additional monitoring tools. Here are the native utilities you can use:

# Basic interface statistics
$ ifconfig eth0

# Continuous monitoring (refresh every 1 second)
$ watch -n 1 ifconfig eth0

For more detailed and programmable access to interface statistics:

# View raw network interface data
$ cat /proc/net/dev

# Sample output:
Inter-|   Receive                                                |  Transmit
 face |bytes    packets errs drop fifo frame compressed multicast|bytes    packets errs drop fifo colls carrier compressed
  eth0: 12345678 98765   0    0    0     0          0         0 9876543  54321   0    0    0     0       0          0

The sysstat package (usually pre-installed) provides excellent historical monitoring:

# Install if not present (requires sudo)
$ sudo yum install sysstat

# View current network usage
$ sar -n DEV 1 5

# Sample output:
Linux 3.10.0-957.el7.x86_64 (hostname)     01/01/2023     _x86_64_    (4 CPU)

12:00:01 AM     IFACE   rxpck/s   txpck/s    rxkB/s    txkB/s   rxcmp/s   txcmp/s  rxmcst/s
12:00:02 AM      eth0      2.00      1.00      0.12      0.08      0.00      0.00      0.00

For persistent monitoring, you can create a bash script:

#!/bin/bash

INTERFACE="eth0"
DELAY=1

while true; do
  RX1=$(cat /sys/class/net/${INTERFACE}/statistics/rx_bytes)
  TX1=$(cat /sys/class/net/${INTERFACE}/statistics/tx_bytes)
  sleep $DELAY
  RX2=$(cat /sys/class/net/${INTERFACE}/statistics/rx_bytes)
  TX2=$(cat /sys/class/net/${INTERFACE}/statistics/tx_bytes)
  
  RX_DIFF=$(( (RX2 - RX1) / DELAY ))
  TX_DIFF=$(( (TX2 - TX1) / DELAY ))
  
  echo "$(date +%H:%M:%S) RX: $(numfmt --to=iec $RX_DIFF)/s TX: $(numfmt --to=iec $TX_DIFF)/s"
done

The modern ip command provides interface statistics:

$ ip -s link show eth0

2: eth0:  mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
    link/ether 00:16:3e:7a:1b:2f brd ff:ff:ff:ff:ff:ff
    RX: bytes  packets  errors  dropped overrun mcast   
    123456789  987654   0       0       0       0      
    TX: bytes  packets  errors  dropped carrier collsns 
    987654321  123456   0       0       0       0      

On a standard RHEL system without the ability to install additional packages, we have several native tools available for monitoring network interface traffic:

# Basic interface statistics
$ cat /proc/net/dev

# Continuous monitoring with watch
$ watch -n 1 "cat /proc/net/dev | grep eth0"

# Using traditional ifconfig
$ ifconfig eth0

The /proc/net/dev file provides detailed statistics about each network interface. The output includes bytes received/transmitted, packets, errors, and more:

Inter-|   Receive                                                |  Transmit
 face |bytes    packets errs drop fifo frame compressed multicast|bytes    packets errs drop fifo colls carrier compressed
  eth0: 14567892  102345    0    0    0     0          0         0  4567890   78901    0    0    0     0       0          0

For real-time monitoring, you can combine basic commands:

# Simple refresh every second
$ while true; do clear; date; cat /proc/net/dev | grep eth0; sleep 1; done

# More advanced version showing rates
$ watch -n 1 "ifconfig eth0 | grep 'RX bytes\|TX bytes'"

To estimate interface utilization percentage, you need to know the interface speed:

# Get interface speed (in Mb/s)
$ ethtool eth0 | grep Speed

# Calculate utilization script
prev_rx=$(cat /proc/net/dev | grep eth0 | awk '{print $2}')
prev_tx=$(cat /proc/net/dev | grep eth0 | awk '{print $10}')
sleep 1
curr_rx=$(cat /proc/net/dev | grep eth0 | awk '{print $2}')
curr_tx=$(cat /proc/net/dev | grep eth0 | awk '{print $10}')
rx_rate=$(( (curr_rx - prev_rx) * 8 / 1000 ))
tx_rate=$(( (curr_tx - prev_tx) * 8 / 1000 ))
echo "RX: $rx_rate Kb/s, TX: $tx_rate Kb/s"

If sysstat package is installed (common on RHEL), sar provides excellent network monitoring:

# Real-time network interface statistics
$ sar -n DEV 1

# Historical data (if collected)
$ sar -n DEV -f /var/log/sa/sa$(date +%d -d yesterday)

For long-term monitoring, create a simple logging script:

#!/bin/bash
LOG_FILE="/var/log/network_stats.log"
INTERFACE="eth0"

while true; do
    TIMESTAMP=$(date '+%Y-%m-%d %H:%M:%S')
    STATS=$(cat /proc/net/dev | grep "$INTERFACE")
    echo "$TIMESTAMP - $STATS" >> "$LOG_FILE"
    sleep 60
done

Remember to make the script executable and consider running it as a service if needed for continuous monitoring.