Addressing and interfaces
Before configuring anything, plan the addresses. Inside your network, you number from your own space. Here everything comes out of 198.51.100.0/24:
| Range | Used for |
|---|---|
| 198.51.100.0/25 | The LAN on core1 (198.51.100.1 is the gateway) |
| 198.51.100.224/28 | Point-to-point links between routers, one /31 each |
| 198.51.100.240/28 | Loopbacks, one /32 per router |
| The rest | Spare, and covered by the blackhole route for the aggregate |
| Router | Loopback | Links |
|---|---|---|
| core1 | 198.51.100.241 | eth0 .225 → edge1, eth1 .227 → edge2, eth2 LAN |
| edge1 | 198.51.100.242 | eth0 203.0.113.1 → upstream, eth1 .224 → core1, eth2 .228 → edge2 |
| edge2 | 198.51.100.243 | eth0 192.0.2.25 on the IX, eth1 .226 → core1, eth2 .229 → edge1 |
Why loopbacks? A loopback address isn't tied to any physical interface, so it's up as long as the router is up. Use it as the router ID for OSPF and BGP, and as the source and destination of every iBGP session. If one link fails, the session simply follows the IGP's new path to the loopback.
The external addresses don't change: edge1 takes over R1's transit /31, and edge2 takes over R1's IX address.
set system host-name 'core1'
set interfaces loopback lo address '198.51.100.241/32'
set interfaces ethernet eth0 address '198.51.100.225/31'
set interfaces ethernet eth0 description 'CORE1-TO-EDGE1'
set interfaces ethernet eth1 address '198.51.100.227/31'
set interfaces ethernet eth1 description 'CORE1-TO-EDGE2'
set interfaces ethernet eth2 address '198.51.100.1/25'
set interfaces ethernet eth2 description 'LAN'- Line 2: The loopback: a /32 that is up as long as the router is.
- Lines 3–6: Two /31 links, one to each edge.
- Lines 7–8: The LAN, same as R1's in the previous lesson.
set system host-name 'edge1'
set interfaces loopback lo address '198.51.100.242/32'
set interfaces ethernet eth0 address '203.0.113.1/31'
set interfaces ethernet eth0 description 'TRANSIT-UPSTREAM'
set interfaces ethernet eth1 address '198.51.100.224/31'
set interfaces ethernet eth1 description 'EDGE1-TO-CORE1'
set interfaces ethernet eth2 address '198.51.100.228/31'
set interfaces ethernet eth2 description 'EDGE1-TO-EDGE2'- Lines 3–4: The transit link, unchanged from R1.
- Lines 5–8: Internal links to core1 and to edge2.
set system host-name 'edge2'
set interfaces loopback lo address '198.51.100.243/32'
set interfaces ethernet eth0 address '192.0.2.25/24'
set interfaces ethernet eth0 description 'IX-PEERING-LAN'
set interfaces ethernet eth1 address '198.51.100.226/31'
set interfaces ethernet eth1 description 'EDGE2-TO-CORE1'
set interfaces ethernet eth2 address '198.51.100.229/31'
set interfaces ethernet eth2 description 'EDGE2-TO-EDGE1'- Lines 3–4: The IX port, unchanged from R1.
- Lines 5–8: Internal links to core1 and to edge1.