5 IP Routing Flashcards
What are routing protocols ?
Routers use routing protocols to dynamically find all networks within the greater internetwork and to ensure that all routers have the same routing table. Routing protocols are also employed to determine the best path a packet should take through an internetwork to get to its destination most efficiently. RIP, RIPv2, EIGRP, and OSPF are examples of the most common routing protocols.
What are routed protocols ?
Once all routers know about all networks, a routed protocol can be used to send user data (packets) through the established enterprise. Routed protocols are assigned to an interface and determine the method of packet delivery. Examples of routed protocols are IP and IPv6.
What is static routing ?
The static routing method requires someone to
hand-type all network locations into the routing table.
What is dynamic routing ?
when dynamic routing is used, a protocol on one router communicates with the same protocol running on neighboring routers. The routers then update each other about all the networks they know about and place this information into the routing table. If a change occurs in the network, the dynamic routing protocols automatically inform all routers about the event.
Using the ‘show ip route’ command on a router, what does L - local, C - connected, S - static, mean ?
C means that the networks listed are directly connected.
L means local host route. Each local route has a /32 prefix, defining a route just for one address in order to more efficiently forward packets to the router itself.
S means static
What is the packet-forwarding technique, Process Switching ?
This process is extremely complex and involves looking up every destination in the routing table and finding the exit interface for every packet.
What is the packet-forwarding technique, Fast Switching ?
This solution was created to make the slow performance of process switching faster and more efficient. Fast switching uses a cache to store the most recently used destinations so that lookups are not required for every packet. Caching the exit interface of the destination device, plus the layer 2 header, dramatically improved performance.
What is the packet-forwarding technique, Cisco Express Forwarding (CEF) ?
This is Cisco’s newest packet forwarding, performance optimizing creation, and it’s the default method used on all the latest Cisco routers. CEF makes many different cache tables that enhance performance and is change triggered, not packet triggered. Translated, this means that when the network topology changes, the cache changes along with it.
Routing Protocols / Distance Vector
The distance-vector protocols in use today find the best path to a remote network by judging distance. In RIP routing, each instance where a packet goes through a router is called a hop, and the route with the least number of hops to the network will be chosen as the best one. The vector indicates the direction to the remote network. RIP is a distance-vector routing protocol and periodically sends out the entire routing table to directly connected neighbors.
Routing Protocols / Link State
In link-state protocols, also called shortest-path-first (SPF) protocols, the routers each create three separate tables. One of these tables keeps track of directly attached neighbors, one determines the topology of the entire internetwork, and one is used as the routing table. Link-state routers know more about the internetwork than any distance vector routing protocol ever could. OSPF is an IP routing protocol that’s completely linkstate. Link-state routing tables are not exchanged periodically. Instead, triggered updates containing only specific link-state information are sent. Periodic keepalives in the form of hello messages, which are small and efficient, are exchanged between directly connected neighbors to establish and maintain neighbor relationships.
Routing Protocols / Distance Vector
Advanced distance-vector protocols use aspects of both distance-vector and link-state protocols, and EIGRP is a great example. EIGRP may act like a link-state routing protocol because it uses a Hello protocol to discover neighbors and form neighbor relationships and because only partial updates are sent when a change occurs. However, EIGRP is still based on the key distance-vector routing protocol principle that information about the rest of the network is learned from directly connected neighbors.
Routing Information Protocol (RIP)
Routing Information Protocol (RIP) is a true distance-vector routing protocol. RIP sends the complete routing table out of all active interfaces every 30 seconds. It relies on hop count to determine the best way to a remote network, but it has a maximum allowable hop count of 15 by default, so a destination of 16 would be considered unreachable. RIP works okay in very small networks, but it’s super inefficient on large networks with slow WAN links or on networks with a large number of routers installed. It’s completely useless on networks that have links with variable bandwidths! RIP version 1 uses only classful routing, which means that all devices in the network must use the same subnet mask. This is because RIP version 1 doesn’t send updates with subnet mask information in tow. RIP version 2 provides something called prefix routing and does send subnet mask information with its route updates. This is called classless routing.
Three types of routing
The three types of routing are:
static (in which routes are manually configured at the CLI)
dynamic (in which the routers share routing information via a routing protocol)
default routing (in which a special route is configured for all traffic without a more specific destination network found in the table).
