W2·A2 - Bridge the network

Time: 20 min

Needs:: A1's topology

GNS3 project:: w02-a1-dedicated-links (reuse it)

Do this - build it

On H1:

nmcli con add type bridge ifname br0 con-name br0 connection.autoconnect-slaves 1
nmcli con mod eth0 type bridge-slave master br0
nmcli con mod eth1 type bridge-slave master br0
nmcli con mod br0 ipv4.method manual ipv4.addresses 192.168.10.1/24
nmcli con up br0

Give the bridge a few moments to activate, then:

ip -brief addr show

Do the same on H2 and assign 192.168.10.2/24 to br0

Do the same on H3 and assign 192.168.10.3/24 to br0

What just happened

• nmcli con add type bridge ifname br0 creates a new type of interface called a bridge and gives it the name br0.
  • con-name br0: tells NetworkManager to save this interfaces configuration under the name br0
  • connection.autoconnect-slaves 1: tells NetworkManager to start the associated physical interfaces when this interface is activated.
• nmcli con mod eth0 type bridge-slave master br0 tells NetworkManager to treat the physical interface named eth0 as a port of br0. The next command does the same for eth1
  • the result is that the devices on the other ends of both eth0 (H2 Ethernet0) and eth1 (H3 Ethernet0) are now on the same link
• We then assign an address to the bridge interface itself
• Repeating this on H2 and H3 essentially places the three nodes on the same link, instead of the three distinct links we had previously.

Do this - test it

On H1:

ping -c1 192.168.10.2
ping -c1 192.168.10.3

What just happened

• H1 is still able to reach H2 and H3, but it now needs just one address to achieve this.
• The physical topology is still mesh, but the logical topology is something akin to a star topology

Do this

• Stop all three nodes
• Delete H2 and H3, then rename H1 as SW
• Drag two VPCS and cable them on to SW

Log on to SW as root, then:

nmcli con mod br0 -ipv4.addresses 192.168.10.1/24 \
ipv4.method disabled ipv6.method disabled

nmcli con up br0

On PC1:

ip 192.168.10.11/24
save

On PC2:

ip 192.168.10.12/24
save

On PC1:

ping 192.168.10.12 -c 1

What just happened

• SW is just H1 in new clothes. We disabled IP to show that a bridge is just a link, a medium, and does not need an address
• PC1 and PC2 are cabled to the two ends of the bridge and are able to communicate through it.
• You've just created your first "switch"!

If it went wrong