- 2073 Magh · 12 marks
Redundant network for IOE Pulchowk campus
Short answer
Use single-mode OS2 fibre between buildings (3,000 m total) because 400 m exceeds copper limits. Each department gets two L3 distribution switches with routed links to a stacked core pair; access switches use LACP and RSTP. Deploy 55 boxes CAT6, 9 access switches, 6 distribution switches, 2 core switches, and 15 APs.
Design the redundant network for IOE Pulchowk campus with 4 departments including ISP department which are around 400 m apart from each other. Three departments have 5 labs each with around 24 computers in each room. ISP contains server farm with server like DNS, DHCP, Email, FTP and webserver and the main internet router which will be connected to upstream provider. Propose appropriate equipment (L1, L2 and L3) and physical wires for the network design.
Assumptions
- Four buildings: the ISP department (hub with server farm and main router) and three departments (Dept-1, Dept-2, Dept-3). Each department is about 400 m from the ISP building. This distance rules out copper (90 m limit), so the buildings are linked with fibre.
- Each department building has 5 labs x 24 PCs = 120 PCs, plus 1 AP per lab (5 APs) = 125 drops. Average horizontal run 40 m.
- Servers: DNS, DHCP, Email, FTP, Web. One upstream provider as stated, with a second link as an optional backup.
Redundant design
Upstream ISP
|
[Edge Router]
|
[Firewall]
|
[Core-1]====LACP====[Core-2] ISP building
| | | | | |
| | +--Server farm(2 SW)--+
| | |
Fibre route A (400 m) Route B (400 m, other path)
| |
+-----+------+------+---------+------+
[Dist-1a/1b] [Dist-2a/2b] [Dist-3a/3b] one pair per dept
| | |
3 access SW 3 access SW 3 access SW (48-port)
Labs 1-5 Labs 1-5 Labs 1-5
- Core: two L3 switches in the ISP building, stacked/LACP, so a core failure is invisible to users.
- Distribution: each department has two L3 distribution switches. Each one is uplinked over a different fibre route to a different core switch, and OSPF routes between them. Because these links are routed (L3), there is no L2 loop.
- Access: within each department building, access switches connect to both distribution switches by LACP and run RSTP with BPDU guard.
- Servers: NIC teaming to two server-farm switches. The router uses HSRP/VRRP and a backup link.
Equipment and wires
| Layer | Item | Qty (total) |
|---|---|---|
| L1 | CAT6 UTP, 305 m box (375 drops x 40 m x 1.1 = 16,500 m) | 55 boxes |
| L1 | Single-mode OS2 6-core armoured fibre, 2 routes x 3 buildings x 500 m (400 m + slack) | 3,000 m |
| L1 | Patch panels 24-port CAT6 (6 per building) | 18 |
| L1 | Fibre patch panel 12-port LC | 8 |
| L1 | CAT6 patch cords 2 m / 1 m | 375 / 375 |
| L1 | LC-LC fibre patch cords, 10G SFP+ LR modules | 24 / 28 |
| L1 | Faceplates and jacks (single port) | 375 |
| L2 | 48-port PoE access switch (3 per building) | 9 |
| L2 | 24-port server-farm switch | 2 |
| L3 | Distribution L3 switch 24-port + SFP+ (2 per building) | 6 |
| L3 | Core L3 switch (ISP building) | 2 |
| L3 | Edge router, firewall | 1, 1 (+1 each for HA) |
| Other | Wireless AP (5 per department) | 15 |
| Other | Servers: DNS, DHCP, Email, FTP, Web | 5 |
| Other | Racks, UPS (one pair per building) | 4, 4 |
The fibre is single-mode so that 10 Gbps works over 400 m and later upgrades are easy; multimode OM3 supports 10G only up to about 300 m, so it is not enough.
IP plan (10.10.0.0/16)
Each lab has 24 PCs, a gateway and an AP, so a /27 (30 hosts) is used.
| Block | Subnet | Notes |
|---|---|---|
| Dept-1 labs 1-5 | 10.10.1.0/27, .32, .64, .96, .128 (/27 each) | VLAN 11-15 |
| Dept-1 Wi-Fi / mgmt | 10.10.1.160/27, 10.10.1.224/27 | |
| Dept-2 labs 1-5 | 10.10.2.0 - 10.10.2.128 (/27 each) | VLAN 21-25 |
| Dept-3 labs 1-5 | 10.10.3.0 - 10.10.3.128 (/27 each) | VLAN 31-35 |
| Server farm DMZ (Web, Mail, FTP) | 10.10.10.0/27 | |
| Internal servers (DNS, DHCP) | 10.10.10.32/27 | |
| Core-distribution links | 10.10.250.0/30 each | OSPF area 0 |
DHCP is relayed from the server farm to every lab VLAN. A single Internet-facing address block from the provider is used for NAT and the public servers.
✓ Answer checked by Claude Opus 5.5 (high effort)
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