Sonali & Janata Bank Officer (IT) — Exam: 14.10.2023 (MIST)প্রশ্ন ও সমাধান

Routing is the process by which routers determine and forward the best path for packets from source to destination, using metrics (hop count, bandwidth, delay, load) maintained in a routing table.

Types:

• Static Routing (non-adaptive): admin manually configures routes — simple, low overhead, but doesn't adapt to topology changes; suits small/stable networks.
• Default Routing: a "catch-all" route used when no specific route matches (e.g., the gateway of last resort to reach the Internet).
• Dynamic Routing (adaptive): routers exchange information via protocols (RIP, OSPF, BGP, EIGRP) to automatically learn and update routes as topology changes.

Ad hoc routing benefit: in a mobile ad hoc network (MANET), nodes join/leave/move without any fixed infrastructure. Ad hoc routing (e.g., AODV, DSR) lets nodes dynamically discover and forward routes for each other, giving: rapid deployment with no fixed infrastructure needed (military, disaster relief); self-healing around failed/moved nodes; no single point of failure; and lower infrastructure cost.

Shortest path algorithm: Dijkstra's algorithm — used by link-state protocols like OSPF to compute the shortest-path tree from a router to every destination, based on link cost.

graph TD
    A((A)) -- 2 --> B((B))
    A -- 5 --> C((C))
    B -- 1 --> C
    B -- 4 --> D((D))
    C -- 1 --> D

Shortest path A→B→C→D costs 2+1+1 = 4, beating both A→C→D (5+1=6) and A→B→D (2+4=6).

Exam takeaway: static = manual/simple/small networks, dynamic = automatic/scalable/large networks, default = fallback route; Dijkstra's shortest-path-first algorithm underlies OSPF, the most common link-state IGP.

A firewall is a security device/software that monitors and filters incoming/outgoing network traffic against a defined rule set, forming a barrier between a trusted internal network and an untrusted external one (e.g., the Internet).

Major types:

1. Packet-Filtering Firewall (Layer 3/4) — inspects header fields (IP, port) against ACL rules; fast but stateless.
2. Stateful Inspection Firewall — tracks each connection's state in a table, so decisions consider the traffic's context.
3. Proxy/Application-Layer Firewall (Layer 7) — acts as an intermediary, inspecting full application content (e.g., HTTP payload).
4. Circuit-Level Gateway (Layer 5) — validates the TCP handshake/session without inspecting packet content.
5. Next-Generation Firewall (NGFW) — combines stateful inspection with deep packet inspection, intrusion prevention, and application/user awareness.

graph LR
    INT["Internal/Trusted Network"] --- FW{{"Firewall"}} --- EXT(("Internet / Untrusted"))
    FW -->|"allow"| A["Permitted traffic"]
    FW -->|"deny"| D["Blocked traffic"]

Exam takeaway: firewalls progress from simple (stateless packet filtering) to comprehensive (NGFW with application awareness + IPS) — choose based on how much visibility into the traffic's actual content is required.