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Router Design

Historical router-design reference. This project is a MUD-side gateway, not an I3 router. Exact inter-router topology and conflict policy are controlled by router operators.

Overview

Routers form the backbone of the Intermud-3 network, maintaining connectivity between all muds and handling packet routing.

Router Connectivity

Inter-Router Network

  • Routers create, open, and maintain MUD mode TCP sessions with each other router
  • Forms a fully connected network (every router connects to every other router)
  • Each router maintains status of all inter-router links
  • Link information used for routing around failed links until reestablishment

Router State Management

Each router maintains:

  • Complete list of all muds on the Intermud
  • Information associated with each mud
  • Up/down/rebooting state for each mud
  • Which router each mud is connected to
  • Complete channel list and membership information

List Synchronization

Routers synchronize two primary lists: mudlist and channel list.

Token-Based Synchronization

  • Each list state has a unique token
  • Routers can provide deltas between tokens or complete lists
  • Tokens guarantee uniqueness using current time

Token Generation

new_token = max(old_token + 1, time())

This ensures:

  • Tokens are unique even if generated within the same second
  • Tokens always increase monotonically
  • Time-based ordering is maintained

Conflict Resolution

When two routers generate deltas simultaneously:

  1. Token Ordering: If tokens t1 and t2 exist where t1 < t2

    • Final token = max(t1, t2)

  2. Receipt Order Issues:

    • If router receives t1 before t2: Normal operation
    • If router receives t2 before t1: Conflict resolution needed

  3. Alter-Token Protocol:

    • Conflicting delta gets new token = t2 + 1
    • Recirculated through router network
    • Duplicates ignored based on altered-token origin

Synchronization Packets

List Delta

({
    "XXXlist-delta",      // XXX = mud or chan
    5,
    originator_mudname,   // Router
    0,
    "*",                  // Router broadcast
    0,
    token,
    list_delta_info
})

List Altered

({
    "XXXlist-altered",    // XXX = mud or chan
    5,
    originator_mudname,   // Router
    0,
    "*",                  // Router broadcast
    0,
    altered_token,
    list_delta_info
})

Packet Routing

Routing Rules

Routing based entirely on originator/target fields:

  • No knowledge of packet types required
  • Provides flexibility for extensions
  • Likely increases routing speed

Routing Algorithm

Based on target_mudname:

  1. If target is connected to this router: Deliver directly
  2. If target is connected to another router: Forward to that router
  3. If target is the router itself: Pass to router processes
  4. If target is broadcast (0): Deliver to all connected muds

Failed Link Handling

When inter-router link fails:

  • Router detects failed link
  • Updates routing tables to route around failure
  • Attempts to reestablish connection
  • Updates other routers about link status

Channel Management

Routers maintain three channel lists:

  1. Unfiltered selective admission channels
  2. Unfiltered selective banning channels
  3. Filtered selective admission channels

For each channel, routers store:

  • Channel type (admission/banning/filtered)
  • Owning mud
  • List of admitted/banned muds
  • Current listeners by mud

Channel Message Routing

  1. Mud sends channel message to router
  2. Router determines recipient muds based on:
    • Channel membership lists
    • Current listener status
  3. For filtered channels:
    • Route to host mud for filtering
    • Receive filtered message back
    • Distribute to recipients
  4. Forward messages to appropriate muds

Performance Considerations

Efficiency Features

  • Routing based solely on target fields (fast lookup)
  • Delta updates minimize data transfer
  • Caching of routing information
  • Direct inter-router links avoid hop delays

Load Balancing

  • Muds can be reassigned to different routers
  • Preferred router can be changed programmatically
  • Distributes connection load across router network

Reliability Features

Failover Support

  • Multiple routers provide redundancy
  • Muds store complete router list
  • Automatic failover to backup routers
  • Graceful handling of router failures

State Persistence

  • Muds maintain mudlist_id across connections
  • Muds maintain chanlist_id across connections
  • Routers can provide appropriate deltas on reconnection

Security

Authentication

  • Password-based mud authentication
  • New muds receive random passwords from routers
  • Passwords validate mud identity across connections
  • Prevents mud impersonation

Validation

  • Packet format validation
  • Source mud verification
  • Channel permission enforcement
  • Service availability checking

Implementation Notes

  • Routers must support all protocol versions
  • Translation between protocol versions as needed
  • Error packets for unsupported operations
  • Maintains backward compatibility