Chapter 3 - Dynamic Routing

Dynamic Routing Advantages and Disadvantages Dynamic routing is the best choice for large networks

Adv: Suitable in all topologies where multiple routers are required. generally independant of the network size Automatically adapts topology to reroute traffic if possible Dis: Can be more complex to implement Less secure Route depends on the current topology Requires more CPU RAM and link bandwidth

Which dynamic routing protocol was developed to interconnect different Internet service providers?

BGP is a protocol developed to interconnect different levels of ISPs as well as ISPs and some of their larger private clients.

Metrics for finding the best routing path:

Bandwidth Cost Delay Hops

The main components of dynamic routing protocols include:

Data structures - Routing protocols typically use tables or databases for its operations. This information is kept in RAM. Routing protocol messages - Routing protocols use various types of messages to discover neighboring routers, exchange routing information, and other tasks to learn and maintain accurate information about the network. Algorithm - An algorithm is a finite list of steps used to accomplish a task. Routing protocols use algorithms for facilitating routing information and for best path determination.

Based on the partial output from the show ip route command, what two facts can be determined about the RIP routing protocol?

The command no auto-summary has been used on the RIP neighbor router. RIP version 2 is running on this router and its RIP neighbor.

While configuring RIPv2 on an enterprise network, an engineer enters the command network 192.168.10.0 into router configuration mode. What is the result of entering this command?

The interface of the 192.168.10.0 network is sending only version 2 updates.

Static Routing Advantages and Disadvantages

They are not easy to implement in a large network. Managing the static configurations can become time consuming. If a link fails, a static route cannot reroute traffic. Adv Easy to implement in small networks Very secure Route to the destination is always the same No routing algorithm or update required. less CPU RAM required.

Sending out unneeded updates on a LAN impacts the network in three ways:

Wasted Bandwidth - Bandwidth is used to transport unnecessary updates. Because RIP updates are either broadcasted or multicasted, switches also forward the updates out all ports. Wasted Resources - All devices on the LAN must process the update up to the transport layers, at which point the devices will discard the update. Security Risk - Advertising updates on a broadcast network is a security risk. RIP updates can be intercepted with packet sniffing software. Routing updates can be modified and sent back to the router, corrupting the routing table with false metrics that misdirect traffic.

A router is configured to participate in multiple routing protocol: RIP, EIGRP, and OSPF. The router must send a packet to network 192.168.14.0. Which route will be used to forward the traffic?

a 192.168.14.0/26 route that is learned via RIP

A parent route is

a level 1 network route that is subnetted. A parent route can never be an ultimate route. Anything that says variable subnetted

A level 2 child route is

a route that is a subnet of a classful network address. the source of a level 2 route can be a directly connected network, a static route, or a dynamically learned route. Level 2 child routes are also ultimate routes.

A level 1 route is

a route with a subnet mask equal to or less than the classful mask of the network address. Therefore, a level 1 route can be a: Network route - A network route that has a subnet mask equal to that of the classful mask. Supernet route - A supernet route is a network address with a mask less than the classful mask, for example, a summary address. Default route - A default route is a static route with the address 0.0.0.0/0.

An ultimate route is

a routing table entry that contains either a next-hop IPv4 address or an exit interface. Directly connected, dynamically learned, and local routes are ultimate routes.

What type of route has a network address with a subnet mask that is less than the classful equivalent?

a supernet route

Which two statements are true regarding classless routing protocols? (

allows for use of both 192.168.1.0/30 and 192.168.1.16/28 subnets in the same topology sends subnet mask information in routing updates

Which type of route will require a router to perform a recursive lookup?

an ultimate route that is using a next hop IP address on a router that is not using CEF If CEF is not used, a recursive lookup must be performed when a route using a next-hop IP address is selected as the best pathway to forward data.​

steps that are taken by a router in the route look up process when it receives a packet, there is no match, and the packet is eventually dropped.

examining level 1 network routes for the best match examining child routes of the parent route for the best match searching level 1 supernet routes for the best match determining if a default route exists dropping the packet

the default-information originate command

propagates the configured static default route configured into routing protocol updates

Enable RIPv2:

router rip version 2 The RIP process now includes the subnet mask in all updates, making RIPv2 a classless routing protocol.

Router RIP Configuration Mode commands:

router rip - turns on for entire router. network network-address - this will auto summarize the address in routing table. auto-summary - auto network summarization default-information - control distribution of default info network - en routing on a IP network passive-interface = suppress routing updates on interface, any port going to a LANs version- set routing protocol version

Which two types of routes could be used to describe the 192.168.200.0/30 route?

ultimate route level 2 child route

To propagate a default route in RIP, the edge router must be configured with:

A default static route using the ip route 0.0.0.0 0.0.0.0 command. The default-information originate router configuration command. This instructs R1 to originate default information, by propagating the static default route in RIP updates.

The purpose of dynamic routing protocols includes:

Discovery of remote networks Maintaining up-to-date routing information Choosing the best path to destination networks Ability to find a new best path if the current path is no longer available

Static routing has several primary uses, including:

Providing ease of routing table maintenance in smaller networks that are not expected to grow significantly. Routing to and from a stub network, which is a network with only one default route out and no knowledge of any remote networks. Accessing a single default route (which is used to represent a path to any network that does not have a more specific match with another route in the routing table).

Which route would be used to forward a packet with a source IPv6 address of 2001:DB8:F00D:1::1 and a destination IPv6 address of 2001:DB8:CAFE:2::1?

R 2001:DB8:CAFE:2::/64 [120/3] via FE80::201:84FF:FEAC:8501, GigabitEthernet0/0

Remote network entries:

Route source - Identifies how the route was learned. Destination network - Identifies the address of the remote network. Administrative distance (AD) - Identifies the trustworthiness of the route source. The AD for static routes is 1 and the AD for connected routes is 0. Dynamic routing protocols have an AD higher than 1 depending upon the protocol. Metric - Identifies the value assigned to reach the remote network. Lower values indicate preferred routes. The metric for static and connected routes is 0. Next hop - Identifies the IPv4 address of the next router to forward the packet to. Route timestamp - Identifies from when the route was last heard. Outgoing interface - Identifies the exit interface to use to forward a packet toward the final destination.

IPv6 Remote entry identifies the following information:

Route source - Identifies how the route was learned. Common codes include O (OSPF), D (EIGRP), R (RIP), and S (Static route). Destination network - Identifies the address of the remote IPv6 network. Administrative distance - Identifies how trustworthiness of the route source. IPv6 uses the same distances as IPv4. Metric - Identifies the value assigned to reach the remote network. Lower values indicate preferred routes. Next hop - Identifies the IPv6 address of the next router to forward the packet to. Outgoing interface - Identifies the exit interface to use to forward a packet toward the final destination.

IPv6 directly connected route entries display the following information:

Route source - Identifies how the route was learned. Directly connected interfaces have two route source codes (C identifies a directly connected network while L identifies that this is a local route.) Directly connected network - The IPv6 address of the directly connected network. Administrative distance - Identifies the trustworthiness of the route source. IPv6 uses the same distances as IPv4. A value of 0 indicates the best, most trustworthy source. Metric - Identifies the value assigned to reach the remote network. Lower values indicate preferred routes. Outgoing interface - Identifies the exit interface to use when forwarding packets to the destination network.

entries are automatically added to the routing table when the an interface is configured and activated. The entries contain the following information:

Route source - Identifies how the route was learned. Directly connected interfaces have two route source codes. C identifies a directly connected network. Directly connected networks are automatically created whenever an interface is configured with an IP address and activated. L identifies that this is a local route. Local routes are automatically created whenever an interface is configured with an IP address and activated. Destination network - The address of the remote network and how that network is connected. Outgoing interface - Identifies the exit interface to use when forwarding packets to the destination network.

ommon codes for remote networks include:

S - Identifies that the route was manually created by an administrator to reach a specific network. This is known as a static route. D - Identifies that the route was learned dynamically from another router using the EIGRP routing protocol. O - Identifies that the route was learned dynamically from another router using the OSPF routing protocol. R - Identifies that the route was learned dynamically from another router using the RIP routing protocol.

Which route is the best match for a packet entering a router with a destination address of 10.16.0.2?

S 10.16.0.0/24 [1/0] via 192.168.0.9

What is meant by the router must find the best match in the routing table? Best match is equal to the longest match.

The best match is the route in the routing table that has the most number of far left matching bits with the destination IPv4 address of the packet. The route with the greatest number of equivalent far left bits, or the longest match, is always the preferred route.