Routing Protocol

Remote networks could be added to the Routing Table by either relying on Routing Protocol# (dynamic routing) or manually configured by network administrator (Static Routing#).

Routing Control is a #Security Mechanism which enables selection of particular physically secure routes for certain data and allows routing# changes.

Router is a #Network Device operates at Network Layer# which forwards packets from source to destination based on network layers protocols (reading the source and destination IP Address). It will communicate with other routers using Routing Protocol# (dynamic routing) or be manually edited by network administrators (static routing) to maintain or update their Routing Table# that contain optimal routing paths. Of course Router needs to be connected to a network to establish either dynamic routing or static routing.

Network layer is the third layer in #Open Systems Interconnection (OSI) Model, and it is commonly referred as Internet Layer in #Internet Protocol Suite (TCP/IP). This is where most of the communication protocols operate. It is responsible for addressing, packaging and routing functions. The header that it adds to the packet, which is its #Protocol Data Units (PDU) includes the source and destination IP Address# which are unique. Routing# is done in this layer.

In Link-State Routing, aka Shortest Path First (SPF), each #Router needs to know the entire topology of the network with the aid of a database. The database stores link states, that is information about the state of a router’s links, which include IP Address, type of network (Ethernet or serial point-to-point link), cost, and neighbours. This database will be identical to all routers using the same protocol albeit processed independently. The #exchange of topology information (called flooding) only happened upon the initial set-up of the network and when there is a topological change in the network (new router added or router is removed). Since only information specific to the change needs to be propagated, combined with the hierarchical model used by the protocol, it limits the scope of the route changes that occur and provides better scaling than Distance Vector Routing Protocol. Though there still a need for keep alive message between router and its neighbours to detect potential topological changes.

IS-IS is a #classless #Link-State Routing Protocol which has wide adoption by Internet Service Provider (ISP)#. It is a rather harden protocol to used as the attacker couldn’t break into a network routing with IS-IS using other Routing Protocol. It is available for both IPv4# and IPv6#.

IGP or Intradomain Routing Protocols are #Routing Protocol used to exchange routing information and forward packets within the Autonomous System (AS)# (intradomain).

Note: IPsec could be used for router advertisement to prevent forged routing update.

FEC is a specific path through the network of #Multiprotocol Label Switching (MPLS) provider routers and is equal to the destination network, stored in an IP routing table.

EGP or Interdomain Routing Protocols are #Routing Protocol used between the Autonomous System (AS)# (interdomain). Most of them are of type Path-Vector Routing Protocol#.

In Distance Vector Routing, the #Routers share their Routing Table with their direct neighbour(s) (often termed “routing by rumour”) periodically. The table stores routing information which describes the direction (router and the corresponding port) where the packets should be forwarded to and the distance using one of the metrics (See in #Routing Protocol). When a router receives the information via this method, it will undergo a process called distance accumulation, that is, increments the distance by one. By this way, routers within the network are ignorant to its topology. The process is usually done by the Bellman-Ford algorithm.

Convergence is a state when all router’s routing table are at a state of consistency. The convergence time is the time it takes to routers to share information, calculate the optimal path, and update their Routing Table.

Classless Routing Protocols are the Routing Protocols that don’t follow the Address Classes subnet masking instead favour the Variable-Length Subnet Masking (VLSM)#. All protocols will include network mask when sending the routing information to other Network Device. It is aimed to replace Classful Routing Protocols.

Classful Routing Protocols are the Routing Protocols# that follow the Fix-Length Subnet Masking#. However, as the networking technologies advanced, most Classful Routing Protocols are phased out in favour of Classless Routing Protocols due to the limitation of Classful Routing Protocols to travel to different Address Classes since the routing update doesn’t include the network mask.

Cisco IOS is a collection of network operating systems used on Cisco Network Devices#, usually stored at the flash of the device or TFTP server. It can be used from input and output devices. It also provides the mean for memory management, process management, file systems management, security management, hardware management, network interface configuration, and enabling routing# and switching# functions.

AD is a numeric value that specifies the preference of a particular route source# which range from 0 to 255. The lower the value, the more trust the Router will be on the source. The following table shows the AD value for each route source.