q31-network-configuration

Énoncé§

Solve this question on: web-srv1

1. Assign the static IPv4 address 192.168.50.10/24 to interface eth1, with gateway 192.168.50.1 and DNS 1.1.1.1. Make it persistent.
2. Add a static route to 10.20.0.0/16 via 192.168.50.254.
3. Set the system hostname to web-srv1.lan persistently.
4. Write the MAC address of eth0 into /opt/course/31/mac.

Solution§

Inspect the current configuration§

ip addr show                                    # ip a
ip -br addr                                     # brief
ip link show
ip route                                        # routing table
ip -6 route
ip neigh                                        # ARP / neighbours
ss -tulnp                                       # listening sockets
resolvectl status                               # DNS resolver (systemd-resolved)
cat /etc/resolv.conf

Step 1 — Static IP§

NetworkManager (nmcli) — RHEL/Fedora/Ubuntu desktop§

nmcli con show                                  # list profiles
nmcli con add type ethernet ifname eth1 con-name eth1-static \
      ipv4.method manual \
      ipv4.addresses 192.168.50.10/24 \
      ipv4.gateway 192.168.50.1 \
      ipv4.dns "1.1.1.1 9.9.9.9"
nmcli con up eth1-static
nmcli con mod eth1-static ipv4.dns-search "lan"

Netplan (Ubuntu server)§

Edit /etc/netplan/01-netcfg.yaml:

network:
  version: 2
  renderer: networkd
  ethernets:
    eth1:
      addresses: [192.168.50.10/24]
      routes:
        - to: default
          via: 192.168.50.1
      nameservers:
        addresses: [1.1.1.1, 9.9.9.9]

Apply:

sudo netplan try            # apply with rollback on failure
sudo netplan apply

systemd-networkd§

Create /etc/systemd/network/10-eth1.network:

[Match]
Name=eth1

[Network]
Address=192.168.50.10/24
Gateway=192.168.50.1
DNS=1.1.1.1

sudo systemctl restart systemd-networkd

/etc/network/interfaces (legacy Debian)§

auto eth1
iface eth1 inet static
    address 192.168.50.10/24
    gateway 192.168.50.1
    dns-nameservers 1.1.1.1

sudo ifup eth1

Step 2 — Routes§

Temporary (lost on reboot):

sudo ip route add 10.20.0.0/16 via 192.168.50.254
sudo ip route del 10.20.0.0/16
sudo ip route add default via 192.168.50.1

Persistent via NetworkManager:

nmcli con mod eth1-static +ipv4.routes "10.20.0.0/16 192.168.50.254"
nmcli con up eth1-static

Step 3 — Hostname§

hostnamectl set-hostname web-srv1.lan
cat /etc/hostname
# also update /etc/hosts to map 127.0.1.1 web-srv1.lan web-srv1

Step 4 — MAC address§

ip -br link show eth0 | awk '{print $3}' > /opt/course/31/mac
# or:
cat /sys/class/net/eth0/address > /opt/course/31/mac

Diagnostics§

ping -c 4 1.1.1.1
ping6 -c 4 fe80::1%eth0
traceroute 8.8.8.8
mtr 8.8.8.8
dig +short example.com
nslookup example.com
host example.com
ss -s                                  # socket summary
nmap -sn 192.168.50.0/24               # discover hosts (with permission)
tcpdump -i eth0 -nn port 80            # capture

IPv6 quick reference§

ip -6 addr add 2001:db8::1/64 dev eth0
ip -6 route add default via 2001:db8::ff
sysctl -w net.ipv6.conf.all.autoconf=0
sysctl -w net.ipv6.conf.all.accept_ra=0

Disable IPv6: see q25-sysctl-kernel-parameters.