Unit VI

1. Unit VI Devices, Backbone networks and SONET Prepared by : Mr. Badgujar D D SIT,Lonavala

2. Connecting devices • Repeaters and Hubs : Physical Layer • Bridge/L2 Switch : Data Link Layer • Router /L3 Switch : Network Layer • Gateway : In all OSI Layers

3. Hubs • Passive Hub : It just a connector. It connects the wires coming from different branches. • Active Hub : It is actually a multiport repeater. It is normally used to create physical connections between stations in a physical star topology Hierarchy of Hubs

4. Repeater • This is operates in only physical layer. This will repeat the signal. This is used where the distance is more. This will only extends the length of LAN. • Repeater does not connect two LAN’s but it will connects two segments of one LAN . • This device carrying two ports one is incoming and other is outgoing. • Repeater is regenerator not an amplifier , Amplifier amplifies whatever fed to it noise and signal also, If repeater receives this it will create copy, bit for bit at the original strength

5. Bridge • It operates in Physical and DLL • When it operates in Physical , it regenerates the signal it receives. • When operates at DLL , the bridge can check the physical MAC address contained in frame. • It will act as Traffic controller between the LAN. Depends on the MAC address it will forward / drop the frame. • If frame is to be forwarded the decision must specify the port. A bridge has a table that maps addresses to ports.

6. Transparent Bridge • Is a bridge in which the stations are completely unaware of the bridge existence. If a bridge is added / deleted from n/w , reconfiguration of the stations is unnecessary. • According to IEEE 802.1 d specification a system must meet following criteria : • Frames must be forwarded from one station to another. • The forwarding table is automatically made by learning frame movement in the n/w • Loops in the system must be prevented.

7. Forwarding : A transparent bridge must correctly forward the frames. • Learning : The old bridge has the static forwarding table .i.e. At the time of installation the table is fed statically. This process is simple but requires modification if we change the NIC Card, or add more station in n/w. • A better solution is dynamic table that gradually learns from the frames movement and maps addresses to ports automatically. • Destination address is used for the forwarding decision , Source address is used for adding entries to the table and for updating purposes.

8. A B E 1 3 Bridge • Original Table is empty. • When A send Frame to D , the bridge don’t have any entry in its table. The frame goes out all three ports ; the frame is flooded in the n/w from source address bridge learns that A in connected to Port 1 and adds entry in it Table • Address || Port A ||1 This is after A to D 2 F C D

9. When E send packet to A then it has entry for A so it will forwards to port 1 only. It adds the source address E and port No. 3 in its table • B sends to C so it don’t have entry for C so it floods the packet inside the n/w and adds the entry for B with port 1. • In this way bridge learns the things.

10. Looping :These works fine if there is no redundant bridge in the system. The n/w admin makes the system more reliable by putting more than 1 bridges , if one bridge fails another can take over. But redundancy will create loops in the system. Fig. Shows the e.g. • Initially the bridge table is empty . A A D B LAN 1 1 1 Address Port Address Port Bridge 1 Bridge 2 2 2 LAN 2 C D

11. Every bridge floods the frame Now LAN1 has 2 copies of the frame Two Copies of the frame on LAN1 A A D A D B LAN 1 1 1 Address Port Address Port A 2 Bridge 1 Bridge 2 A 2 2 2 LAN 2 C D Both Bridge forwards frame This process continues

12. Spanning Tree • In Graph theory a tree that doesn’t contain any loop. • In bridged LAN ,creating a topology in which each LAN can be reached from any other LAN through one path only. • To find the spanning tree, we need to assign a cost (metric) to each arc. It may be path with minimum hops , the path with minimum delay, or path with max bandwidth. • We are going with minimum hop. The hop count consider from Bridge to LAN =1 and from LAN to Bridge=0

13. 0 1 LAN1 B2 B1 1 0 0 0 • From Bridge to LAN 1 • From LAN to Bridge 0 1 1 0 1 LAN 3 LAN 2 B3 1 0 1 1 0 0 0 1 B5 B4 LAN 4 1 0

14. Creating A Spanning Tree • Every bridge has built-in ID which is commonly a serial no. The bridge with min. serial no is selected as the root bridge. Assumes that B1 with smallest ID. • The algo. Tries to find the shortest path from the root bridge or LAN . The shortest path is from root to destination. • The combination of the shortest path creates the shortest tree. Which is shown in fig.

15. 1 1 LAN1 B2 B1 1 LAN 3 2 LAN 2 1 B3 B5 B4 LAN 4 1 2 2 Shortest Path

16. Root LAN1 B2 B1 LAN 3 LAN 2 B3 B5 B4 LAN 4 Spanning Tree

17. The ports which are not a part of Spanning Tree are called as Blocking Port . • The ports which forwards the frames are called as forwarding port, which forwards the frame which bridge receives

18. Dynamic Algorithm • Spanning tree requires manual entries . Each bridge carrying a software that carries the process dynamically . The bridges sends the special message called bridge protocol data unit(BPDU) to update spanning tree. The spanning tree is updated when there is a change in the system such as failure of the bridge or an addition / deletion of bridges.

19. Source Routing Bridges • In source routing bridges the filtering, forwarding and blocking of frames is performed by source station. • The sending station defines the frame must visit the bridges along with their nos. these are included in the frame . The frame contains not only source and destination address but also the addresses on bridge that frame must visited. • Commonly used in Token Ring Network

20. Two-Layer Switches(L2) • This can be act at Physical and DLL. This is nothing but Multiport Bridge and perform better than bridge. U can configure the ports of this switch. The filtering decision is made up depends on the MAC address of the frame it received. It has buffer to hold the frames for processing.

21. Router • Operates in Network Layer. • Routing Table • Routing will be done statically and dynamically also.

22. L3 Switch • It is layer 3 switch it is faster than the router. The fabric in L3 allows fast table lookup and forwarding

23. Gateway • Commonly it is software. Operates in all layers of OSI layer. Has a capability of protocol conversion also called as Protocol Converter.

24. Backbone Network • Bus Network • Star Network

25. Virtual LAN • If two LANs are separate. If a virtual connection between two LANs allows the communication between 2 computer then this concept is called as VLAN as a LAN configured by software. • VLAN Creates broadcast domain

26. Switch • If the group members are changed then we have rewire the connections physically. Group 1 Group 2 Group 3

27. Switch with VLAN Software VLAN1 • The switch is divided into VLAN. The idea is divide the LAN into logical segment instead of physical segments . A LAN can be divided into several LAN called VLAN. Each VLAN is a work group in the organisation. If a person moves from one group to another then there is no need of change of physical configuration. • All members of VLAN can receive the broadcast message sent to the particular VLAN VLAN2 VLAN3

28. Backbone Switch Switch with VLAN Software Switch with VLAN Software VLAN1 • VLAN topology allows the grouping of stations connected to different switches in a VLAN. This is good configuration for a company with two separate buildings. The people in the two different building may be in same workgroup using VLAN VLAN2 VLAN3

29. Membership in VLAN • To create a VLAN the vendors use Port No.,MAC address, IP addresses, Multicast IP addresses, combination of any two/3 • Port Nos.: Some VLAN Vendors uses port nos. as memberships characteristics • MAC Address • IP address

30. Multicast IP addresses : Uses multicast IP address as membership characteristics • Combination

31. Configuration • Manual configuration : Admin types the port nos. IP addresses • Automatic : The stations are automatically connected or disconnected from a VLAN using criteria defined by the admin. E.g the admin gives the project no as the criteria for being a member of group . When the users changes the project, he/ she automatically migrated to new VLAN.

32. Semiautomatic : The initializing is done manually and migration is done automatically.

33. Communication between Switches • In multiswitched backbone each switch must know not only which station belongs to which VLAN, but also the membership of stations connected to other switches. • 3 methods have been advised for this purpose

34. Table Maintenance :When a station sends a broadcast frame to its group members , the switch creates an entry in a table and records station membership . The switches send their tables to one another periodically for updating. • Frame Tagging : When a frame is traveling between switches , an extra header is added to the MAC frame to define the destination VLAN. The frame TAG is used by receiving switches to determine the VLAN to be receiving the broadcast message

35. Time Division Multiplexing: The connection between switches is divided into timeshared channels . E.g. If the total no. of VLAN in a backbone is 5 each trunk is divided into 5 channels. The traffic destined for VLAN 1 travels in channel 1, the traffic destined for VLAN 2 travels in channel 2 and so on. • The receiving switch determines the destination VLAN by checking the channel from which the frame is arrived.

36. IEEE std. for VLAN • 802.1 subcommittee passed a std. called 802.1 Q that defines the format for Tagging. It also allows the multivendor equipment in VLAN.

37. Advantages of VLAN • Cost and Time Reduction : The stations can move logically there is no need of physical reconfiguration so it saves time and cost. • Creating Virtual Work Group : VLAN can be used to create virtual work group. E.g. In campus environment, professors working on the same project can send broadcast messages to one another without the necessity of belonging to the same department. This can reduce traffic if the multicasting capability of IP was previously used.

38. Security : People belonging to the same work group can send broadcast message with the guaranteed assurance that users in other groups will not receive these messages.