- 2072 Kartik · 6 marks
Multicast and unicast routing protocols
Short answer
Unicast routing (RIP, OSPF, BGP) delivers one-to-one using distance-vector, link-state, or path-vector algorithms. Multicast routing delivers one-to-many to group addresses (224.0.0.0/4) using IGMP for membership and protocols like PIM-SM/DM, DVMRP, MOSPF, CBT to build shared or source-based trees, saving bandwidth by replicating only at branch points.
Explain briefly about multicast routing protocols and unicast routing protocols.
Routing protocols decide how a router builds its table. Unicast routing serves one source to one destination; multicast routing serves one source to a group of receivers.
Unicast routing protocols
Used for one-to-one delivery. They are grouped by the way routes are computed.
| Protocol | Type | Key points |
|---|---|---|
| RIP | Distance vector | Bellman-Ford; metric is hop count (max 15); updates every 30 s; slow convergence |
| OSPF | Link state | Each router floods link-state advertisements, runs Dijkstra; cost metric; areas; fast convergence |
| BGP | Path vector | Between autonomous systems (inter-domain); policy based; runs over TCP port 179 |
- Intra-domain (inside an AS): RIP, OSPF. Inter-domain: BGP.
Multicast routing protocols
Packets are sent once and copied by routers only where the paths to group members split. Group addresses are in 224.0.0.0/4 (Class D). IGMP lets a host tell its local router which group it joins; the routing protocols then build a delivery tree.
| Protocol | Idea |
|---|---|
| DVMRP | Distance vector; flood and prune with reverse path forwarding; source-based trees |
| MOSPF | Extension of OSPF; every router knows the group membership; source-based trees |
| PIM-DM | Flood and prune, uses the existing unicast table |
| PIM-SM | Group-shared tree rooted at a rendezvous point (RP); suits sparse groups |
| CBT | Core-based tree shared by all senders |
Source -> R1 -> R2 -> Host in group
\-> R3 -> Host in group (one copy per link)
Multicast saves bandwidth compared with sending many unicast copies.
✓ Answer checked by Claude Opus 5.5 (high effort)
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