Review Jaringan Komputer 1. Gambar 1. Soal UAS Jarkom 1

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2 Modul 1 Ethernet Switching Review Jaringan Komputer 1 Gambar 1. Soal UAS Jarkom 1 Gambar diatas adalah sebuah struktur jaringan, dan baru dipasang untuk pertama kali, tugas anda adalah : 1. Tentukan jenis kabel pada masing masing device,apakah crossover, straight over, atau rollover 2. Berikan IP Address pada masing masing PC 3. Jelaskan, apakah komputer dalam rancangan diatas sudah dapat terkoneksi 4. Jelaskan,jika ada 3 ip address pada gambar dibawah A. IP : SM : B. IP : SM :

3 C. IP : SM : Apakah A dan B dapat terhubung, A dan C dapat terhubung, atau B dan C dapat terhubung, jelaskan jawab anda dengan jelas dan singkat. Ethernet Switching Gambar 2. Operasi Bridge Gambar diatas adalah bagaimana operasi bridge dalam mengisi table MAC address dan cara pengiriman hub maupun bridge, dengan kondisi dimana jaringan baru dioperasikan pertama kali, prosesnya sebagai berikut The bridge has just been started so the bridge table is empty. The bridge just waits for traffic on the segment. When traffic is detected, it is processed by the bridge. Host A pings Host B. Since the data is transmitted on the entire collision domain segment, both the bridge and Host B process the packet.

4 The bridge adds the source address of the frame to its bridge table. Since the address was in the source address field and the frame was received on Port 1, the frame must be associated with Port 1 in the table. The destination address of the frame is checked against the bridge table. Since the address is not in the table, even though it is on the same collision domain, the frame is forwarded to the other segment. The address of Host B has not been recorded yet. Host B processes the ping request and transmits a ping reply back to Host A. The data is transmitted over the whole collision domain. Both Host A and the bridge receive the frame and process it. The bridge adds the source address of the frame to its bridge table. Since the source address was not in the bridge table and was received on Port 1, the source address of the frame must be associated with Port 1 in the table. The destination address of the frame is checked against the bridge table to see if its entry is there. Since the address is in the table, the port assignment is checked. The address of Host A is associated with the port the frame was received on, so the frame is not forwarded. Host A pings Host C. Since the data is transmitted on the entire collision domain segment, both the bridge and Host B process the frame. Host B discards the frame since it was not the intended destination. The bridge adds the source address of the frame to its bridge table. Since the address is already entered into the bridge table the entry is just renewed. The destination address of the frame is checked against the bridge table. Since the address is not in the table, the frame is forwarded to the other segment. The address of Host C has not been recorded yet. Host C processes the ping request and transmits a ping reply back to Host A. The data is transmitted over the whole collision domain. Both Host D and the bridge receive the frame and process it. Host D discards the frame since it is not the intended destination. The bridge adds the source address of the frame to its bridge table. Since the address was in the source address field and the frame was received on Port 2, the frame must be associated with Port 2 in the table. The destination address of the frame is checked against the bridge table to see if its entry is present. The address is in the table but it is associated with Port 1, so the frame is forwarded to the other segment. When Host D transmits data, its MAC address will also be recorded in the bridge table. This is how the bridge controls traffic between to collision domains.

5 These are the steps that a bridge uses to forward and discard frames that are received on any of its ports. Bridges Gambar 3. Broadcast Domain Umumnya bridge hanya mempunyai dua port dan membagi collision domain dalam dua bagian. Semua keputusan bridge berdasarkan tujuan MAC Address yang berada pada layer 2 dan tidak berpengaruh pada layer 3. bridge akan membagi collision domain tetapi tidak mempengaruhi broadcast domain. Switch biasanya cepat, multi-port bridge. Setiap port switch merupakan collision tersendiri. Jika dalam jaringan dan switch mempunyai 20 port atau nodes, maka akan terdapat 20 collision domains. switch secara dynamic dibangun dan di kembangkan oleh table CAM content-addressable memory, yang menyimpan informasi MAC di setiap port

6 Switch Operation Gambar 4. Operasi Switch Full Duplex Gambar 5.

7 Network Latency Gambar 6. Latency Latency adalah waktu yang diperlukan untuk sebuah paket untuk berpindah dari satu lokasi ke lokasi lain, variasi dari kondisi yang dapat menyebabkan latency : Media delays dapat disebabkan keterbatasan kecepatan sinyal dalam membawa data melalui media physical. Circuit delays dapat disebabkan oleh proses elektronik sepanjang jalur yang digunakan. Software delays dapat disebabkan dalam hal software untuk menentukan dalam implementsi switching dan protocol yang digunakan. Delays dapat disebabkan metode switching dalam pembacaan isi frame dari awal hingga akhir frame baru dikirmkan ke MAC address tujuan. Mode Switch Cut Through ( Real Time ) atau FastForward Switch LAN membaca hanya alamat tujuan (6 byte pertama yang mengikuti preamble ) ke buffer onboardnya ( chip memory di dalam sebuah switch ) setelah itu dilakukan, switch akan melihat ke alamat tujuan hardware di dalam table switching MAC, menentukan outgoing interface, dan kemudian menforward frame menuju tujuannya melalui interface tersebut. Sebuah switch cut through benar benar membantu mengurangi latency karena ia mulai menforward frame begitu ia membaca alamat tujuan dan menentukan outgoing interface.

8 Gambar 7. Mode Switch Cut Through FragmentFree ( Cut through yang di modifikasi ) Sebuah bentuk modifikasi dari switching cut through dimana switch menunggu apa yang disebut collision window ( 64 byte pertama dari sebuah frame ) lewat sebelum melakukan forwarding. Ini karena jika sebuah paket memiliki sebuah error collision, biasanya selalu terjadi dalam 64 byte pertama. Ini 7amper frame akan dicek sampai field data untuk memastikan tidak ada fragmentasi yang terjadi. Mode fragmenfree menyediakan pengecekan error yang lebih baik dibandingkan mode cut through dengan 7amper tidak ada peningkatan latency, Mode ini adalah metode switching default untuk switch switch seri 1900 Store and Forward Adalah metode switching LAN cisco yang utama. Pada metode store and forward, switch LAN menduplikasi atau mengcopy seluruh frame ke buffer onboardnya dan kemudian menghitung cylic redundancy check ( CRC ), Karena ia menduplikasi seluruh frame, latency melalui switch menjadi bervariasi sesuai dengan panjang frame. Frame dibuang jika mengandung sebuah error CRC juga dibuang jika ia terlalu pendek ( lebih pendek dari 64 byte pertama termasuk CRC ) atau jika terlalu panjang ( lebih dari 1518 byte termasuk CRC ). Jika frame tidak memiliki error, switch LAN melihat kealamat hardware tujuan di table

9 forwarding atau table switching untuk menentukan outgoing interface yang benar. Ketika ia menemukannya, frame akan diforward ke tujuan melalui interface tersebut. Gambar 8.Store and Forward How a frame is switched to the destination port is a trade off between latency and reliability. A switch can start to transfer the frame as soon as the destination MAC address is received. This is called cut-through packet switching and results in the lowest latency through the switch. However, no error checking is available. The switch can also receive the entire frame before it is sent to the destination port. This gives the switch software an opportunity to verify the Frame Check Sequence (FCS). If the frame is invalid, it is discarded at the switch. Since the entire frame is stored before it is forwarded, this is called store-and-forward packet switching. A compromise between cut-through and store-and-forward packet switching is the fragment-free mode. Fragment-free packet switching reads the first 64 bytes, which includes the frame header, and starts to send out the packet before the entire data field and checksum are read. This mode verifies the reliability of the addresses and LLC protocol information to ensure the data will be handled properly and arrive at the correct destination. When cut-through packet switching is used, the source and destination ports must have the same bit rate to keep the frame intact. This is called symmetric switching. If the bit rates are not the same, the frame must be stored at one bit rate before it is sent out at the other bit rate. This is known as asymmetric switching. Store-and-forward mode must be used for asymmetric switching.

10 Referensi : [1]. Lammle Todd, CCNA Cisco Certified Network Associate, Elexmedia komputindo [2]. Materi CCNA 1 V 3.1