Konfigurasi RIP: Memanipulasi metric RIP
Sebuah serial link yang dipakai sebagai backup telah ditambahkan pada Ernest-Barney, lihat gambar topologi yang baru dibawah ini. Link tersebut hanya boleh digunakan sebagai backup jika route/jalur via Andy mengalami kegagalan. Masalahnya adalah jalur antara subnet 10.33.0.0 Barney dan subnet 10.33.32.0 Ernest memiliki metric sejauh 1 hop jika melalui link serial dan sejauh 2 hop jika melalui link ethernet via Andy. Pada keadaan normal, RIP akan memilih serial link sebagai jalur terbaik.
Untuk itu, metric RIP harus dimanipulasi agar link ethernet yang memiliki metric 2 hop lebih diutamakan dari pada link serial yang sejauh 1 hop.
Metric route dapat dimanipulasi dengan perintah offset-list. Perintah tersebut menentukan besar angka yang akan ditambahkan pada metric dari entri route dan mengacu pada sebuah access list untuk menentukan entri route yang mana saja yang akan dimodifikasi. Syntax dari perintah tersebut seperti berikut:
offset-list {access-list-number | name} { in | out} offset [type number]
konfigurasi pada Ernest dapat berupa sebagai berikut:
Ernest(config)#access-list 1 permit 10.33.0.0 0.0.0.0 Ernest(config)#router rip Ernest(config-router)#network 192.168.12.0 Ernest(config-router)#network 10.0.0.0 Ernest(config-router)#offset-list 1 in 2 s1/0 Ernest(config-router)#^Z Ernest#
Access list yang tertulis diatas mengidentifikasikan sebuah route subnet 10.33.0.0. Syntax dari offset list mengatakan, “Periksa semua advertisements RIP yang datang dari interface s1/0. tambahkan 2 hop metric untuk setiap entri route yang sesuai dengan address-address yang ditentukan dalam access list 1“
Berikut contoh hasil debug pada Ernest
Ernest#debug ip rip RIP protocol debugging is on Ernest# *Mar 1 00:59:51.839: RIP: sending v1 update to 255.255.255.255 via Ethernet0/0 (192.168.12.196) *Mar 1 00:59:51.843: RIP: build update entries *Mar 1 00:59:51.843: network 10.0.0.0 metric 1 *Mar 1 00:59:51.847: RIP: sending v1 update to 255.255.255.255 via Ethernet0/0 (10.33.75.2) *Mar 1 00:59:51.851: RIP: build update entries *Mar 1 00:59:51.851: subnet 10.33.16.0 metric 1 *Mar 1 00:59:51.855: subnet 10.33.32.0 metric 1 *Mar 1 00:59:56.459: RIP: sending v1 update to 255.255.255.255 via Serial1/0 (10.33.25.2) *Mar 1 00:59:56.463: RIP: build update entries *Mar 1 00:59:56.463: subnet 10.0.0.0 metric 2 *Mar 1 00:59:56.467: subnet 10.33.0.0 metric 3 *Mar 1 00:59:56.467: subnet 10.33.32.0 metric 1 *Mar 1 00:59:56.471: subnet 10.33.64.0 metric 1 *Mar 1 00:59:56.471: network 192.168.12.0 metric 1 *Mar 1 00:59:56.847: RIP: sending v1 update to 255.255.255.255 via Loopback1 (10.33.35.1) *Mar 1 00:59:56.851: RIP: build update entries *Mar 1 00:59:56.851: subnet 10.0.0.0 metric 2 *Mar 1 00:59:56.855: subnet 10.33.0.0 metric 3 *Mar 1 00:59:56.855: subnet 10.33.16.0 metric 1 *Mar 1 00:59:56.859: subnet 10.33.48.0 metric 2 *Mar 1 00:59:56.859: subnet 10.33.64.0 metric 1 *Mar 1 00:59:56.863: network 192.168.12.0 metric 1 *Mar 1 00:59:56.863: network 192.168.83.0 metric 2 *Mar 1 01:00:10.291: RIP: received v1 update from 10.33.25.1 on Serial1/0 *Mar 1 01:00:10.295: 10.0.0.0 in 2 hops *Mar 1 01:00:10.295: 10.33.0.0 in 3 hops *Mar 1 01:00:10.299: 10.33.32.0 in 3 hops *Mar 1 01:00:10.299: 10.33.48.0 in 1 hops *Mar 1 01:00:10.303: 192.168.83.0 in 1 hops *Mar 1 01:00:11.871: RIP: received v1 update from 192.168.12.195 on Ethernet0/0 *Mar 1 01:00:11.875: 10.0.0.0 in 1 hops *Mar 1 01:00:11.875: 192.168.12.64 in 1 hops *Mar 1 01:00:11.879: 192.168.83.0 in 1 hops *Mar 1 01:00:11.883: RIP: received v1 update from 10.33.75.1 on Ethernet0/0 *Mar 1 01:00:11.883: 10.33.0.0 in 2 hops *Mar 1 01:00:11.887: 10.33.48.0 in 1 hops *Mar 1 01:00:11.887: 192.168.12.0 in 1 hops *Mar 1 01:00:11.891: 192.168.83.0 in 1 hops *Mar 1 01:00:19.435: RIP: sending v1 update to 255.255.255.255 via Ethernet0/0 (192.168.12.196) *Mar 1 01:00:19.439: RIP: build update entries *Mar 1 01:00:19.439: network 10.0.0.0 metric 1 *Mar 1 01:00:19.443: RIP: sending v1 update to 255.255.255.255 via Ethernet0/0 (10.33.75.2) *Mar 1 01:00:19.447: RIP: build update entries *Mar 1 01:00:19.447: subnet 10.33.16.0 metric 1 *Mar 1 01:00:19.451: subnet 10.33.32.0 metric 1 *Mar 1 01:00:22.739: RIP: sending v1 update to 255.255.255.255 via Serial1/0 (10.33.25.2) *Mar 1 01:00:22.743: RIP: build update entries *Mar 1 01:00:22.743: subnet 10.0.0.0 metric 2 *Mar 1 01:00:22.747: subnet 10.33.0.0 metric 3 *Mar 1 01:00:22.747: subnet 10.33.32.0 metric 1 *Mar 1 01:00:22.751: subnet 10.33.64.0 metric 1 *Mar 1 01:00:22.751: network 192.168.12.0 metric 1 *Mar 1 01:00:25.999: RIP: sending v1 update to 255.255.255.255 via Loopback1 (10.33.35.1) *Mar 1 01:00:26.003: RIP: build update entries *Mar 1 01:00:26.003: subnet 10.0.0.0 metric 2 *Mar 1 01:00:26.007: subnet 10.33.0.0 metric 3 *Mar 1 01:00:26.007: subnet 10.33.16.0 metric 1 *Mar 1 01:00:26.011: subnet 10.33.48.0 metric 2 *Mar 1 01:00:26.011: subnet 10.33.64.0 metric 1 *Mar 1 01:00:26.015: network 192.168.12.0 metric 1 *Mar 1 01:00:26.015: network 192.168.83.0 metric 2 *Mar 1 01:00:38.079: RIP: received v1 update from 192.168.12.195 on Ethernet0/0 *Mar 1 01:00:38.083: 10.0.0.0 in 1 hops *Mar 1 01:00:38.083: 192.168.12.64 in 1 hops *Mar 1 01:00:38.087: 192.168.83.0 in 1 hops *Mar 1 01:00:38.091: RIP: received v1 update from 10.33.75.1 on Ethernet0/0 *Mar 1 01:00:38.091: 10.33.0.0 in 2 hops *Mar 1 01:00:38.095: 10.33.48.0 in 1 hops *Mar 1 01:00:38.095: 192.168.12.0 in 1 hops *Mar 1 01:00:38.099: 192.168.83.0 in 1 hops *Mar 1 01:00:39.003: RIP: received v1 update from 10.33.25.1 on Serial1/0 *Mar 1 01:00:39.007: 10.0.0.0 in 2 hops *Mar 1 01:00:39.011: 10.33.0.0 in 3 hops *Mar 1 01:00:39.011: 10.33.32.0 in 3 hops *Mar 1 01:00:39.015: 10.33.48.0 in 1 hops *Mar 1 01:00:39.015: 192.168.83.0 in 1 hops *Mar 1 01:00:48.807: RIP: sending v1 update to 255.255.255.255 via Ethernet0/0 (192.168.12.196) *Mar 1 01:00:48.811: RIP: build update entries *Mar 1 01:00:48.811: network 10.0.0.0 metric 1 *Mar 1 01:00:48.815: RIP: sending v1 update to 255.255.255.255 via Ethernet0/0 (10.33.75.2) *Mar 1 01:00:48.819: RIP: build update entries *Mar 1 01:00:48.819: subnet 10.33.16.0 metric 1 *Mar 1 01:00:48.823: subnet 10.33.32.0 metric 1 *Mar 1 01:00:50.835: RIP: sending v1 update to 255.255.255.255 via Serial1/0 (10.33.25.2) *Mar 1 01:00:50.839: RIP: build update entries *Mar 1 01:00:50.839: subnet 10.0.0.0 metric 2 *Mar 1 01:00:50.843: subnet 10.33.0.0 metric 3 *Mar 1 01:00:50.843: subnet 10.33.32.0 metric 1 *Mar 1 01:00:50.847: subnet 10.33.64.0 metric 1 *Mar 1 01:00:50.847: network 192.168.12.0 metric 1
Penambahan yang ditentukan dalam offset list merubah hop count subnet 10.33.0.0/20 via s1/0 dari 1 menjadi 3 hop. Dengan begitu route ethernet dengan 2 hop akan lebih diutamakan.
Perhatikan tabel routing Ernest berikut, Ernest dapat mencapai subnet 10.33.0.0/20 via Andy sejauh 2 hop.
Ernest#sh ip route 192.168.12.0/27 is subnetted, 3 subnets R 192.168.12.64 [120/1] via 192.168.12.195, 00:00:20, Ethernet0/0 R 192.168.12.0 [120/1] via 10.33.75.1, 00:00:20, Ethernet0/0 C 192.168.12.192 is directly connected, Ethernet0/0 R 192.168.83.0/24 [120/1] via 192.168.12.195, 00:00:20, Ethernet0/0 [120/1] via 10.33.75.1, 00:00:20, Ethernet0/0 [120/1] via 10.33.25.1, 00:00:19, Serial1/0 10.0.0.0/20 is subnetted, 6 subnets R 10.0.0.0 [120/1] via 192.168.12.195, 00:00:20, Ethernet0/0 C 10.33.32.0 is directly connected, Loopback1 R 10.33.48.0 [120/1] via 10.33.75.1, 00:00:20, Ethernet0/0 [120/1] via 10.33.25.1, 00:00:19, Serial1/0 R 10.33.0.0 [120/2] via 10.33.75.1, 00:00:20, Ethernet0/0 C 10.33.16.0 is directly connected, Serial1/0 C 10.33.64.0 is directly connected, Ethernet0/0 Ernest#
Dan Barney dapat mencapai subnet 10.33.32.0/20 via Andy sejauh 2 hop.
Barney#sh ip route R 192.168.12.0/24 [120/1] via 192.168.83.1, 00:00:05, Ethernet0/0 [120/1] via 10.33.55.2, 00:00:05, Ethernet0/0 [120/1] via 10.33.25.2, 00:00:00, Serial1/0 C 192.168.83.0/24 is directly connected, Ethernet0/0 10.0.0.0/20 is subnetted, 6 subnets R 10.0.0.0 [120/1] via 192.168.83.1, 00:00:05, Ethernet0/0 R 10.33.32.0 [120/2] via 10.33.55.2, 00:00:05, Ethernet0/0 C 10.33.48.0 is directly connected, Ethernet0/0 C 10.33.0.0 is directly connected, Loopback1 C 10.33.16.0 is directly connected, Serial1/0 R 10.33.64.0 [120/1] via 10.33.55.2, 00:00:05, Ethernet0/0 [120/1] via 10.33.25.2, 00:00:00, Serial1/0
Tersedia juga beberapa opsi konfigurasi offset list yang lain. jika tidak ada interface yang ditetapkan, maka list akan memodifikasi setiap update yang masuk atau keluar yang ditentukan dalam access list pada setiap interface. Jika tidak ada access list yang digunakan, offset list akan memodifikasi semua update yang masuk atau keluar.
Perlu ketelitian yang lebih untuk memilih apakah menggunakan offset list pada advertisement yang datang atau yang keluar. Terlebih lagi jika router terhubung pada network broadcast, harus dipertimbangkan lagi apakah satu router harus membroadcast advertisement yang telah dimodifikasi pada semua neighbor ataukah satu router harus memodifikasi semua advertisement yang datang.
Juga harus lebih berhati-hati saat mengimplementasikan offset list pada route yang sedang digunakan. Jika sebuah offset list menyebabkan router next-hop mengadvertise metric yang lebih besar daripada yang selama ini dia advertise, maka route akan ditandai sebagai unreachable sampai holddown timer berakhir.
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