S2 C8 The Routing Table: A Closer Look

Routing Table Structure

Routing table entries come from the following sources

  • Directly connected networks
  • Static routes
  • Dynamic routing protocols

Level 1 Routes //co subnet <= subnet mask major network

  • Supernet Route
  • Default Route
  • Network Route //Mang giu nguyen ko chia nho /8 /16 /24
  • Parent Route //Ko co next hop, exit int

Level 2 Routes

  • Child Route

Ultimate Route //La cac route day dc goi tin di nho 2 tham so next hop, exit int(tru Parent Route thi cac loai Route khac deu la Ultimate Route)

Classfull vs Classless

Classless

  • Hien thi Subnet mask cua major (Ca Parent va Child)
  • Co variably subnetted

Routing Table Lookup Process

  • Dau tien khi nhan duoc goi tin voi dia chi dich
  • Router se so sanh tu tren xuong duoi voi cac Route lv1 tru ra Default Route va Super Net (vi day la Route tong hop)
  • Neu Route lv1 (chi xet Network Route va Parent Route) match voi goi tin thi (so luong bit lam net phu hop voi subnet).
    • Network Route thi day goi tin di ngay
    • Parent Route thi so sanh voi cac Child Route trong Parent Route
      • Neu Child Route phu hop thi se day di, khi co nhieu Child Route phu hop thi se day duong nao match nhieu bit nhat – Longest bit match
      • Neu Child Route khong phu hop thi se xet den qua trinh behavior //co cho su dung classfull hay classless hay khong
        • Neu behavior la classfull thi drop
        • Neu  behavior la classless. So sanh Supernet ma match thi day goi tin. Neu khong thi day theo Default route. Neu khong co Supernet hay Default Route thi drop