Subnetting VLSM – Tracce e soluzioni svolte

Cisco Packet Tracer • Tabelle complete • Metodo matematico

Traccia 1–2 con calcoli, tabelle e checklist operativa (gateway = ultimo host utile).
Traccia 1 (PDF) Traccia 2 (PDF) Pagina Teoria Subnetting
Come usare questa pagina
Convenzione usata nelle soluzioni: Gateway = ultimo host utile della subnet. Per i link WAN p2p si usa /30 (2 host utili) e si assegnano i due IP ai router.
Procedura VLSM (in 6 passi)
  1. Scrivi l’elenco delle reti con host minimi.
  2. Ordina in ordine decrescente (la rete più grande per prima).
  3. Per ogni rete trova h tale che 2h − 2 ≥ H → prefisso / (32 − h).
  4. Calcola la mask (metodo matematico): q = n//8, r = n%8, ottetto = 256 − 2(8−r).
  5. Assegna le subnet in sequenza rispettando l’allineamento (confini corretti della nuova mask).
  6. Compila la tabella: Network, Broadcast, Host min/max, Gateway.
Checklist Packet Tracer
  • Router: IP sulle interfacce + no shut → show ip int brief
  • PC/Server/Stampanti: IP + mask + gateway → ping al gateway
  • Routing: inserisci rotte statiche (o default route sui “rami”) → show ip route
  • Test finale: ping tra sedi/reparti + ping verso DMZ/Server Farm
In laboratorio: gli switch sono solo Layer 2 (nessuna configurazione richiesta). Concentrati su indirizzamento, interfacce router e routing.
Traccia 1 – Campus scolastico + Server Farm (VLSM)

Blocco assegnato: 10.50.0.0/20 – Richiesta: più LAN + 3 link WAN p2p (R1–R2, R1–R3, R1–R4)

Traccia (immagine)
Traccia 1 – Campus scolastico (VLSM)
Figura: 4 router (Core + 2 edifici + Server Farm) con LAN e WAN p2p.
Soluzione guidata (calcolo rapido)
Ordine decrescente usato: 200, 180, 120, 60, 50, 45, 30, 25, 20, poi WAN /30.
  • 200 host → /24 (254 host utili)
  • 180 host → /24 (254)
  • 120 host → /25 (126)
  • 60/50/45 host → /26 (62)
  • 30/25/20 host → /27 (30)
  • WAN p2p (2 host) → /30 (2)
Uso Host min Network Mask Broadcast Host min Host max Gateway
WiFi-Guest (campus) 200 10.50.0.0/24 255.255.255.0 10.50.0.255 10.50.0.1 10.50.0.254 10.50.0.254
Classi-B (R3) 180 10.50.1.0/24 255.255.255.0 10.50.1.255 10.50.1.1 10.50.1.254 10.50.1.254
LAB-A1 (R2) 120 10.50.2.0/25 255.255.255.128 10.50.2.127 10.50.2.1 10.50.2.126 10.50.2.126
LAB-A2 (R2) 60 10.50.2.128/26 255.255.255.192 10.50.2.191 10.50.2.129 10.50.2.190 10.50.2.190
Segreteria/Amministrazione (R1) 50 10.50.2.192/26 255.255.255.192 10.50.2.255 10.50.2.193 10.50.2.254 10.50.2.254
Docenti-B (R3) 45 10.50.3.0/26 255.255.255.192 10.50.3.63 10.50.3.1 10.50.3.62 10.50.3.62
Server Farm (R4) 30 10.50.3.64/27 255.255.255.224 10.50.3.95 10.50.3.65 10.50.3.94 10.50.3.94
IoT-B (R3) 25 10.50.3.96/27 255.255.255.224 10.50.3.127 10.50.3.97 10.50.3.126 10.50.3.126
Stampanti-A (R2) 20 10.50.3.128/27 255.255.255.224 10.50.3.159 10.50.3.129 10.50.3.158 10.50.3.158
WAN R1–R2 2 10.50.3.160/30 255.255.255.252 10.50.3.163 10.50.3.161 10.50.3.162 n/d
WAN R1–R3 2 10.50.3.164/30 255.255.255.252 10.50.3.167 10.50.3.165 10.50.3.166 n/d
WAN R1–R4 2 10.50.3.168/30 255.255.255.252 10.50.3.171 10.50.3.169 10.50.3.170 n/d
Assegnazione IP (gateway + WAN)
  • R1: WiFi-Guest 10.50.0.254/24 • Segreteria 10.50.2.254/26
  • R2: LAB-A1 10.50.2.126/25 • LAB-A2 10.50.2.190/26 • Stampanti-A 10.50.3.158/27
  • R3: Classi-B 10.50.1.254/24 • Docenti-B 10.50.3.62/26 • IoT-B 10.50.3.126/27
  • R4: Server Farm 10.50.3.94/27
  • WAN: R1–R2: R1 10.50.3.161 / R2 10.50.3.162 • R1–R3: R1 10.50.3.165 / R3 10.50.3.166 • R1–R4: R1 10.50.3.169 / R4 10.50.3.170
Routing statico (coerente con la topologia a “stella”)
Suggerimento pratico: sui router “ramo” (R2/R3/R4) usa una default route verso R1.
Su R2
ip route 0.0.0.0 0.0.0.0 10.50.3.161
Su R3
ip route 0.0.0.0 0.0.0.0 10.50.3.165
Su R4
ip route 0.0.0.0 0.0.0.0 10.50.3.169
Su R1 (rotte verso le LAN dietro i rami)
ip route 10.50.2.0 255.255.255.128 10.50.3.162
ip route 10.50.2.128 255.255.255.192 10.50.3.162
ip route 10.50.3.128 255.255.255.224 10.50.3.162
ip route 10.50.1.0 255.255.255.0 10.50.3.166
ip route 10.50.3.0 255.255.255.192 10.50.3.166
ip route 10.50.3.96 255.255.255.224 10.50.3.166
ip route 10.50.3.64 255.255.255.224 10.50.3.170
Verifica: ping tra Edificio A ↔ Edificio B e ping verso Server Farm. Router: show ip route.
Traccia 2 – Azienda HQ + 2 filiali + DMZ (VLSM)

Blocco assegnato: 172.16.32.0/19 – Richiesta: reti HQ, Filiale Nord, Filiale Sud, DMZ + link WAN p2p

Traccia (immagine)
Traccia 2 – Azienda HQ + filiali + DMZ (VLSM)
Figura: HQ (R1) collegato a Filiale Nord (R2), Filiale Sud (R3) e DMZ (R4).
Soluzione guidata (calcolo rapido)
Ordine decrescente usato: 500, 180, 90, 70, 60, 45, 30, 25, 20, 14, poi WAN /30.
  • 500 host → /23 (510)
  • 180 host → /24 (254)
  • 90/70 host → /25 (126)
  • 60/45 host → /26 (62)
  • 30/25/20 host → /27 (30)
  • 14 host → /28 (14)
  • WAN p2p → /30 (2)
Nella traccia compare anche un link R1–R5: qui lo considero come WAN extra/opzionale (riserva o eventuale router/ISP).
Uso Host min Network Mask Broadcast Host min Host max Gateway
Produzione (HQ) 500 172.16.32.0/23 255.255.254.0 172.16.33.255 172.16.32.1 172.16.33.254 172.16.33.254
Uffici (HQ) 180 172.16.34.0/24 255.255.255.0 172.16.34.255 172.16.34.1 172.16.34.254 172.16.34.254
LAN-Nord (R2) 70 172.16.35.0/25 255.255.255.128 172.16.35.127 172.16.35.1 172.16.35.126 172.16.35.126
Ricerca & Sviluppo (HQ) 90 172.16.35.128/25 255.255.255.128 172.16.35.255 172.16.35.129 172.16.35.254 172.16.35.254
Magazzino/Logistica (HQ) 60 172.16.36.0/26 255.255.255.192 172.16.36.63 172.16.36.1 172.16.36.62 172.16.36.62
LAN-Sud (R3) 45 172.16.36.64/26 255.255.255.192 172.16.36.127 172.16.36.65 172.16.36.126 172.16.36.126
Management (HQ) 30 172.16.36.128/27 255.255.255.224 172.16.36.159 172.16.36.129 172.16.36.158 172.16.36.158
IoT-Sud (R3) 25 172.16.36.160/27 255.255.255.224 172.16.36.191 172.16.36.161 172.16.36.190 172.16.36.190
DMZ-Server (R4) 20 172.16.36.192/27 255.255.255.224 172.16.36.223 172.16.36.193 172.16.36.222 172.16.36.222
Stampanti-Nord (R2) 14 172.16.36.224/28 255.255.255.240 172.16.36.239 172.16.36.225 172.16.36.238 172.16.36.238
WAN R1–R2 2 172.16.36.240/30 255.255.255.252 172.16.36.243 172.16.36.241 172.16.36.242 n/d
WAN R1–R3 2 172.16.36.244/30 255.255.255.252 172.16.36.247 172.16.36.245 172.16.36.246 n/d
WAN R1–R4 2 172.16.36.248/30 255.255.255.252 172.16.36.251 172.16.36.249 172.16.36.250 n/d
WAN R1–R5 (opz.) 2 172.16.36.252/30 255.255.255.252 172.16.36.255 172.16.36.253 172.16.36.254 n/d
Assegnazione IP (gateway + WAN)
  • R1 (HQ): Produzione 172.16.33.254/23 • Uffici 172.16.34.254/24 • R&S 172.16.35.254/25 • Magazzino 172.16.36.62/26 • Management 172.16.36.158/27
  • R2 (Nord): LAN-Nord 172.16.35.126/25 • Stampanti-Nord 172.16.36.238/28
  • R3 (Sud): LAN-Sud 172.16.36.126/26 • IoT-Sud 172.16.36.190/27
  • R4 (DMZ): DMZ-Server 172.16.36.222/27
  • WAN: R1–R2: R1 172.16.36.241 / R2 172.16.36.242 • R1–R3: R1 172.16.36.245 / R3 172.16.36.246 • R1–R4: R1 172.16.36.249 / R4 172.16.36.250 • R1–R5: R1 172.16.36.253 / R5 172.16.36.254
Routing statico (schema identico alla Traccia 1)
R2/R3/R4 (e R5 se presente): default route verso R1. R1: rotte verso le reti dietro i rami.
Su R2
ip route 0.0.0.0 0.0.0.0 172.16.36.241
Su R3
ip route 0.0.0.0 0.0.0.0 172.16.36.245
Su R4
ip route 0.0.0.0 0.0.0.0 172.16.36.249
Su R1 (rotte verso Nord, Sud, DMZ)
ip route 172.16.35.0 255.255.255.128 172.16.36.242
ip route 172.16.36.224 255.255.255.240 172.16.36.242
ip route 172.16.36.64 255.255.255.192 172.16.36.246
ip route 172.16.36.160 255.255.255.224 172.16.36.246
ip route 172.16.36.192 255.255.255.224 172.16.36.250
Verifica: ping tra tutte le reti (HQ ↔ Nord ↔ Sud ↔ DMZ). Router: show ip route e show ip int brief.
Riepilogo rapido
  • VLSM: subnet con dimensioni diverse in base agli host richiesti.
  • Regola d’oro: ordina in decrescente e assegna prima le reti più grandi.
  • Calcolo rapido: trova h tale che 2h − 2 ≥ host richiesti → prefisso = 32 − h.
  • Mask (metodo matematico): q = n//8, r = n%8, ottetto = 256 − 2(8−r).
  • Routing: in topologie a stella, sui rami è comoda la default route verso il core; sul core rotte verso i rami.
  • Troubleshooting: show ip int brief, show ip route, ping e tracciamento dei gateway.