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C480 Chapter 6

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verickle's version from 2016-10-19 20:31

Routing Protocol Characteristics

Question Answer
Routing protocola protocol that advertises route information between routers
Routed protocola protocol with an addressing scheme (for example, IP) that defines different network addresses
administrative distance (AD)the feature that routers use in order to select the best path when there are two or more different routes to the same destination from two different routing protocols
metrica value assigned to a route (lower is preferred over higher)
Interior Gateway Protocols (IGPs)operate within an autonomous system, where an autonomous system is a network under a single administrative control
Exterior Gateway Protocols (EGPs)operate between autonomous systems
autonomous system number (ASN)unique identification number (16-bit) assigned to an autonomous system by the Internet Assigned Numbers Authority (IANA)
distance-vector routing protocolsends a full copy of its routing table to its directly attached neighbors
Hold-down timerAfter a router makes a change to a route entry, prevents any subsequent updates for a specified period of time.
Split horizonprevents a route learned on one interface from being advertised back out of that same interface
Poison reversecauses a route received on one interface to be advertised back out of that same interface with a metric considered to be infinite
routing loopformed when an error occurs in the operation of the routing algorithm, and as a result, in a group of nodes, the path to a particular destination forms a loop
link-state routing protocolallows routers to build a topological map of the network. Then, similar to a global positioning system (GPS) in a car, a router can execute an algorithm to calculate an optimal path (or paths) to a destination network.
link-state advertisements (LSAs)communicates the router's local routing topology to all other local routers in the same OSPF area
Dijkstra's shortest path first algorithmfinds the shortest path between a node and every other
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Administrative Distance

Routing Information SourceAdministrative Distance
Directly connected network0
Statically configured network1
EIGRP90
OSPF110
RIP120
External EIGRP170
Unknown of unbelievable255 (considered to be unreachable)
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Routing Protocol Examples

Question Answer
Routing Information Protocol (RIP)A distance-vector routing protocol that uses a metric of hop count.
Open Shortest Path First (OSPF)A link-state routing protocol that uses a metric of cost, which is based on the link speed between two routers.
Intermediate System-to-Intermediate System (IS-IS)This link-state routing protocol is similar in its operation to OSPF. It uses a configurable, yet dimensionless, metric associated with an interface and runs Dijkstra's shortest path first algorithm.
Enhanced Interior Gateway Routing Protocol (EIGRP)A Cisco proprietary protocol.
Border Gateway Protocol (BGP)The only EGP in widespread use today.
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Names of NAT IP Addresses

NAT IP AddressDefinition
Inside localA private IP address referencing an inside device
Inside globalA public IP address referencing an inside device
Outside localA private IP address referencing an outside device
Outside globalA public IP address referencing an outside device
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Address Translation

Question Answer
Dynamic NAT (DNAT)a technique in which multiple public Internet Protocol (IP) addresses are mapped and used with an internal or private IP address
Static NAT (SNAT)a private IP address is mapped to a public IP address, where the public address is always the same IP address
Port Address Translation (PAT)an extension to network address translation (NAT) that permits multiple devices on a local area network (LAN) to be mapped to a single public IP address
ephemeral port numbera short-lived endpoint that is created by the operating system when a program requests any available user port
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Multicast Routing

Question Answer
Multicast Routingprotocols are used to distribute data (for example, audio/video streaming broadcasts) to multiple recipients
Internet Group Management Protocol (IGMP)a communications protocol used by hosts and adjacent routers on IPv4 networks to establish multicast group memberships
IGMP Version 1 (IGMPv1)two messages only: the Membership Query and a Membership Reply
IGMP Version 2 (IGMPv2)a receiver can proactively send a leave message when it no longer wants to participate in a multicast group, allowing the router to prune its interface earlier than it would have
IGMP Version 3 (IGMPv3)Adds a feature called source-specific multicast (SSM), which allows a client to request traffic not only destined for a particular multicast group but also sourced from a specific server.
Protocol Independent Multicast (PIM)routes multicast traffic between multicast-enabled routers
PIM dense mode (PIM-DM)uses a source distribution tree, meaning that an optimal path is formed between the source router in a multicast network (that is, the router closest to the multicast sender) and each last-hop router (the router closest to each multicast receiver). straightforward to implement but generally has poor scaling properties.
PIM sparse mode (PIM-SM)Explicitly builds unidirectional shared trees rooted at a rendezvous point (RP) per group, and optionally creates shortest-path trees per source. Generally scales fairly well for wide-area usage.
shared distribution treeall last-hop routers (routers with downstream multicast receivers) send join messages to the same RP
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Glossary

Question Answer
Administrative distance (AD)A routing protocol’s index of believability. Routing protocols with a smaller AD are considered more believable than routing protocols with a higher AD.
ARP commandCan be used in either the Microsoft Windows or the UNIX environment to see what a Layer 2 MAC address corresponds to in a Layer 3 IP address.
Border Gateway Protocol (BGP)The only EGP in widespread use today. In fact, BGP is considered to be the routing protocol that runs the Internet, which is an interconnection of multiple autonomous systems. BGP is a path-vector routing protocol, meaning that it can use as its metric the number of autonomous system hops that must be transited to reach a destination network, as opposed to the number of required router hops.
Default static routeA default static route is an administratively configured entry in a router’s routing table that specifies where traffic for all unknown networks should be sent.
Distance vectorA category of routing protocol that sends a full copy of its routing table to its directly attached neighbors.
Dynamic NAT (DNAT)A variant of NAT in which inside local addresses are automatically assigned an inside global address from a pool of available addresses.
Enhanced Interior Gateway Routing Protocol (EIGRP)A Cisco proprietary protocol. So, although EIGRP is popular in Cisco-only networks, it is less popular in mixed-vendor networks. Like OSPF, EIGRP is an IGP with very fast convergence and high scalability. EIGRP is considered to be an advanced distance vector or a hybrid routing protocol.
Exterior Gateway Protocol (EGP)A routing protocol that operates between autonomous systems, which are networks under different administrative control. Border Gateway Protocol (BGP) is the only EGP in widespread use today.
Hold-down timersCan speed the convergence process of a routing protocol. After a router makes a change to a route entry, the hold-down timer prevents subsequent updates for a specified period of time. This approach can help stop flapping routes (which are routes that oscillate between being available and unavailable) from preventing convergence.
Interior Gateway Protocol (IGP)A routing protocol that operates within an autonomous system, which is a network under a single administrative control. OSPF and EIGRP are popular examples of IGPs.
Intermediate System-to-Intermediate System (IS-IS)A link-state routing protocol similar in its operation to OSPF. IS-IS uses a configurable, yet dimensionless, metric associated with an interface and runs Dijkstra’s shortest path first algorithm. Although using IS-IS as an IGP offers the scalability, fast convergence, and vendor-interoperability benefits of OSPF, it has not been deployed as widely as OSPF.
Internet Group Management Protocol (IGMP)A multicast protocol used between clients and routers to let routers know which of their interfaces has a multicast receiver attached.
Link-stateA category of routing protocol that maintains a topology of a network and uses an algorithm to determine the shortest path to a destination network.
Link-state advertisement (LSA)Sent by routers in a network to advertise the networks the routers know how to reach. Routers use those LSAs to construct a topological map of a network. The algorithm run against this topological map is Dijkstra’s shortest path first algorithm.
MetricA value assigned to a route. Lower metrics are preferred over higher metrics.
Network Address Translation (NAT)Allows private IP addresses (as defined in RFC 1918) to be translated into Internet-routable IP addresses (public IP addresses).
Next-hopAn IP address on the next router to which traffic should be forwarded.
Open Shortest Path First (OSPF)A link-state routing protocol that uses a metric of cost, which is based on the link speed between two routers. OSPF is a popular IGP because of its scalability, fast convergence, and vendor interoperability.
Poison reverseThis feature of a distance-vector routing protocol causes a route received on one interface to be advertised back out of that same interface with a metric considered to be infinite.
Port Address Translation (PAT)A variant of NAT in which multiple inside local IP addresses share a single inside global IP address. PAT can distinguish between different flows based on port numbers.
Protocol Independent Multicast (PIM)A multicast protocol used between multicast-enabled routers to construct a multicast distribution tree.
Route redistributionAllows routes learned by one routing protocol to be injected into the routing process of another routing protocol.
Routed protocolA protocol with an addressing scheme (for example, IP) that defines different network addresses.
Routing Information Protocol (RIP)A distance-vector routing protocol that uses a metric of hop count. The maximum number of hops between two routers in an RIP-based network is 15. Therefore, a hop count of 16 is considered to be infinite. RIP is considered to be an IGP.
Routing protocolA routing protocol (for example, RIP, OSPF, or EIGRP) that advertises route information between routers, which describes how to reach specified destination networks.
Split horizonThis feature of a distance-vector routing protocol prevents a route learned on one interface from being advertised back out of that same interface.
Static NAT (SNAT)A variant of NAT in which an inside local IP address is statically mapped to an inside global IP address. SNAT is useful for servers inside a network that need to be accessible from an outside network.
Time To Live (TTL)The TTL field in an IP header is decremented once for each router hop. Therefore, if the value in a TTL field is reduced to 0, a router discards the frame and sends a time exceeded ICMP message back to the source.
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