Types of internetworking devices

• Gateways (Levels 1-7, All layers)

• Routers (Level 3, Network layer)

• Bridges (Level 2, Data link layer)

• Brouters (Levels 2 & 3, Data link and network layers)

• Repeaters (Level 1, Physical layer)

Other IEEE 802 project groups

• 802.0 – Executive Committee

• 802.1 – Higher Layer Interfaces

• 802.2 – Logical Link Control

• 802.6 – Metropolitan Area Network (MAN)

• 802.7 – Broadband LAN

• 802.8 – Fiber Optic LAN

• 802.9 – Integrated Voice and Data LAN

• 802.10 – Standards for Interoperable LAN Security

• 802.11 – Wireless Networks

• 802.12 – Demand Priority Access LAN, 100BaseVG-AnyLAN

Function: to keep track of where the packet is going next, it's next 'hop'

Example: With TCP/IP, when the packet reaches it's destination IP address, the destination MAC address will be for that machine

Regenerates signals (more expansion than with repeaters)

Transparent to higher level protocols (on same logical network)

Filters traffic based on physical address (segmenting and security)

E.g. IBM Model 8209 Ethernet to Token Ring Bridge

e.g. Frames from 802.5 (TR) network are packaged as 802.3 (Ethernet) frames, they pass over the CSMA/CD network, then are de-encapsulated by another bridge and put on a third (802.5) network. The Ethernet network doesn't even see the frames

Much faster than translation, allows packets to travel quickly over multiple LANs

Two critical issues arise for such choices:

• Flow control information is necessary to know the relative capacities of bridged segments

• Routing control (segments with multiple links would broadcast redundant frames, which will all arrive at the destination !!! )

Flow control is very important on large active networks

• 80% of traffic on a bridged network is local

• <20% needs to go on the backbone

Spanning Tree Routing Algorithm

• bridges communicate with each other and decide which of them will block and which will allow, thus preventing loops

• Blocking bridges continue to monitor network and when an active bridge fails, they take over

Source Routing Algorithm

• Found in IBM Token Ring networks

• Source broadcasts an 'all-routes' broadcast frame which propagates throughout network.

• Destination replies with the route the frame took, so source specifies that route for duration of the communication

• Therefore, bridges in a 802.5 network rely on the source for routing information

• IBM propose Source Routing Transparent Bridges which would also forward other types of frames, as well as source routing ones

They will only forward frames if they don't know whether the source and destination are on the same segment

This can be a significant factor on local traffic, as it keeps traffic segmented

Confusing

• This is a higher-level service so technically not a bridge

• It is however effective use of bridging

May be used to bridge only selected protocols

Remote

• A LAN segment on one side and a WAN segment on the other

• Output channel usually much lower bandwidth

• Much more complicated to design and implement

• Must be able to buffer inbound traffic and manage time-outs

• Necessary to keep traffic over the remote link to a minimum

Advanced filtering called Virtual LAN (VLAN)

• Port-based grouping

  • Certain ports are assigned to specific VLAN

  • Packets are kept local to that VLAN

• Address-based grouping

  • Certain addresses are assigned to specific VLAN

  • Packets are only forwarded to that VLAN

• Protocol-based grouping

  • Level 3 switching

  • Examines the access protocol and forwards accordingly

• Subnet-based grouping

  • Level 3 switching

  • With TCP/IP, determines and forwards to appropriate subnet

Routers segment extended internetworks into manageable subnets

Operate at Network Layer of OSI

May not have throughput of bridges because of higher resource demand, but current routers can handle 802.3/802.5 traffic without dropping packets

Modern routers may support 15-20 protocols

Forwards packets based on static or dynamic tables

• Static

  • Maintained by system manager

  • Updated as network is modified

• Dynamic

  • Updated as routers talk amongst themselves

  • Uses common protocol such as:

    • Routing Information Protocol (RIP)

    • Open Shortest Path First (OSPF)

Bandwidth now cheap on LANs, so flow control, routing decisions and multi-path management arise mainly in WAN links

Separates networks logically, allowing for

• easier administration and fault isolation

• multiple redundant paths

  • not so for bridges, e.g. Spanning Tree shuts down redundant paths until they are needed

Allows for a port of entry and exit

• Good for security and reducing network congestion

• Good for organizational department separating

Programmable

• Effective management of remote links

• WAN links are most expensive on network so proper management is vital for multi-site organizations

Trend towards using router cards in hubs or wiring concentrators

Processor/Memory/Storage

• Memory is important as it is used to buffer packets during congestion

Physical Interfaces (Ports) Supported

• May be built into box or added with cards

• LAN side

  • Ethernet, Token Ring, ARCnet

• WAN side (telecommunications network)

  • RS-232, V35, RS-442, FDDI, Broadband

Because hardware is similar for routers, brouters, and bridges, upgrades may just require new software

Protocols Supported

• LAN

  • TCP/IP

  • XNS and XNS-based (e.g. Banyan VINES)

  • IPX

  • ISO CLNS

  • DECnet

  • HP Advancenet

  • SDLC

  • AppleTalk

• WAN

  • ATM

  • X.25

  • Frame Relay

  • Switched Multimegabit Data Services (SMDS)

  • Dedicated lines (56Kb – T1)

• Router Protocols

  • RIP

  • OSPF

  • End System-Intermediate System (OSI ES-IS)

  • Intermediate System-Intermediate System (OSI IS-IS)

  • Proprietary vendor protocols

Configuration/Management (Open/Proprietary)

• RS232 serial port for local or modem terminal access

• Provides a simple character oriented interface

• Also maybe possible to connect remotely across the network

• Security

  • Password

  • Restrict access to

    • particular addresses

    • just the serial port

    • ..OR from particular routers

• SNMP (Simple Network Management Protocol)

  • TCP/IP management protocol

  • Does not provide security, so to be avoided

  • Access to view or change settings is done via read-only or read-write community strings

• OSI network management standards

  • Should provide for security

  • Common Management Information Protocol (CMIP)

    • expected to provide management for network devices in general

  • CMIP Over TCP/IP (CMOT)

    • for managing TCP/IP networks in particular

    • until available, proprietary systems are best for security

ALSO at the Data Link layer as a bridge for non-routable protocols

Bridged protocols can propagate through network but techniques such as filtering and learning can reduce congestion

'Broadcast storms'

• If a host looses contact with another host, it issues a broadcast, which a bridge will propagate but a router usually wont

• All hosts must process the broadcast, which if there are enough of, will lead to performance loss, which may induce further broadcasts

• Escalation of transient reliability problem into network failure!

Link State Algorithms