IP Routing Principles
1: In the routing table, a field indicates the source of the routing information. If the field showed the letter C, what would this mean?
** A field showing the letter C would mean that the network is directly connected.
2: In the routing table, how is the next hop indicated?
** In the routing table, the next hop is indicated by the word via followed by an IP address. This is the address of the next logical hop.
3: Cisco distinguishes between the routing and the switching functions. What is the difference?
** The routing function is how the router learns the logical topology of the network. It decides whether the datagram can be routed, which path to select if there is a choice, and to which outgoing interface to queue the datagram. It operates at Layer 3 of the OSI stack.
The switching function is the forwarding of the frame from the inbound interface to an outbound interface. It operates at Layer 2 of the OSI stack, not at Layer 3 like a router, because the routing or Layer 3 function has already been completed.
4: Name the interior IP routing protocols that send the mask with the routing update.
** The interior IP routing protocols that send the mask with the routing update are EIGRP, OSPF, IS-IS, and RIPv2.
5: Does VLSM require a classful or classless routing protocol, and why?
** VLSM requires a classless routing protocol because it needs the subnet mask to be sent with the update.
6: State one of the characteristics of a classful routing protocol.
** The characteristics of a classful routing protocol are as follows:
- It summarizes at the network boundary.
- Routes exchanged between foreign networks are summarized to the NIC number.
- Within the same network (IANA classful network), subnet routes are exchanged by routers.
- All the interfaces on all the routers within a NIC number must share the same subnet mask.
- VLSM is not possible within the network
7: What is the command to show whether a specific network, such as 141.131.6.16, is present in the routing table?
** The command to show whether a specific network, such as 141.131.6.16, is present in the routing table is as follows:
show ip route 141.131.6.16
8: State one major difference between a classful protocol and a classless routing protocol.
** Major differences between classful and classless routing protocols include:
- The capability to use VLSM
- The capability to summarize at an administratively defined boundary, as opposed to summarizing at the classful boundary
- The capability to maximize the logical address space
9: Describe briefly the difference between a routing and routed protocol.
** The routed protocol is the Layer 3 protocol used to transfer data from one end device to another across the network. The routed protocol is the Layer 3 datagram that carries the application data in addition to the upper-layer information.
The routing protocol is the protocol used to send updates between the routers about the networks that exist in the organization, thereby allowing the routing process to determine the path of the datagram across the network.
10: Describe the processes used to build and maintain the routing table.
** There are three steps involved in building and maintaining the routing table. These three processes are independent and include:
The routing protocol, which actually sends the information about the routes or networks within the autonomous system, such as RIPv1, IGRP, EIGRP
The routing table, which receives updates from the routing protocol and provides the forwarding process with information on request
The forwarding process, which determines which path to select from the routing table in order to forward a datagram
11: Give a brief explanation of the switching function.
** The switching function does the following:
- Checks the incoming frame for validity
- Checks whether the frame is addressed (at Layer 2) to the router
- Checks whether the frame is within the scope of the framing criteria (too big or too small)
- Checks whether the frame passes CRC
- Strips the Layer 2 header and trailer from the frame and checks the destination address against the cache entries
- Creates the appropriate frame header and trailer (if there is an entry in cache for the destination address) and forwards the frame to the outbound interface queue
12: What information is contained in the fast switching cache?
** If fast switching is enabled, the datagram is then examined again, and an entry is put into a route cache. The entry in this cache consists of the following:
- An IP prefix
- The output interface
- The link-layer header to be used in forwarding the datagram
13: When would you use the command no auto-summary?
** Some routing protocols, such as BGP, RIPv2, and EIGRP, summarize at the network boundary automatically. Summarization within the NIC number boundary must be configured manually, and therefore autosummarization must first be disabled with the no auto-summary command.
14: When does OSPF send updates, and do they contain the entire routing table?
** Each OSPF router refreshes its LSA every 30 minutes. An LSA will be sent earlier if there is an adjacency change.
15: Network convergence is when a network domain has learned about the new network topology after a change has occurred in the domain. What is considered a network change that would require network convergence?
** The accuracy of the table will be affected by how quickly it responds to changes in the network. These changes include the following:
- Learning new networks
- Learning a better path to an existing network
- Learning that a network is no longer available
- Learning an alternative route to a network
16: When would you consider using a static route in your network?
** A static route would be configured for the following reasons:
- Links that have very low bandwidth, such as dialup links
- The administrator needs control over the link
- The link is a backup to the dynamically learned route
- There is only one path to the remote network, such as a stub network
- The router has very limited resources and cannot run a routing protocol
- The administrator needs to control the routing table to allow a classful protocol and a classless routing protocol to populate the routing table
17: When would you consider using a default route in your network?
** Occasions for using a default route include:
- Connecting to the autonomous system from a stub network
- Connecting to the Internet
18: What command is used to configure ODR on a hub router?
** router odr is the only command needed to be configured on the hub router.
19: When would you consider using a floating static route in your network?
** Floating static routes are used when a backup route is required.
20: Describe some of the characteristics of classless routing protocols.
** Classless routing protocols include OSPF, EIGRP, RIPv2, IS-IS, and BGP.
- The characteristics of a classless routing protocol are:
- Router interfaces within the same network can have different subnet masks (VLSM).
- They support the use of classless interdomain routing (CIDR).
- Some routes can be summarized within the major NIC number. This is done manually.
** A field showing the letter C would mean that the network is directly connected.
2: In the routing table, how is the next hop indicated?
** In the routing table, the next hop is indicated by the word via followed by an IP address. This is the address of the next logical hop.
3: Cisco distinguishes between the routing and the switching functions. What is the difference?
** The routing function is how the router learns the logical topology of the network. It decides whether the datagram can be routed, which path to select if there is a choice, and to which outgoing interface to queue the datagram. It operates at Layer 3 of the OSI stack.
The switching function is the forwarding of the frame from the inbound interface to an outbound interface. It operates at Layer 2 of the OSI stack, not at Layer 3 like a router, because the routing or Layer 3 function has already been completed.
4: Name the interior IP routing protocols that send the mask with the routing update.
** The interior IP routing protocols that send the mask with the routing update are EIGRP, OSPF, IS-IS, and RIPv2.
5: Does VLSM require a classful or classless routing protocol, and why?
** VLSM requires a classless routing protocol because it needs the subnet mask to be sent with the update.
6: State one of the characteristics of a classful routing protocol.
** The characteristics of a classful routing protocol are as follows:
- It summarizes at the network boundary.
- Routes exchanged between foreign networks are summarized to the NIC number.
- Within the same network (IANA classful network), subnet routes are exchanged by routers.
- All the interfaces on all the routers within a NIC number must share the same subnet mask.
- VLSM is not possible within the network
7: What is the command to show whether a specific network, such as 141.131.6.16, is present in the routing table?
** The command to show whether a specific network, such as 141.131.6.16, is present in the routing table is as follows:
show ip route 141.131.6.16
8: State one major difference between a classful protocol and a classless routing protocol.
** Major differences between classful and classless routing protocols include:
- The capability to use VLSM
- The capability to summarize at an administratively defined boundary, as opposed to summarizing at the classful boundary
- The capability to maximize the logical address space
9: Describe briefly the difference between a routing and routed protocol.
** The routed protocol is the Layer 3 protocol used to transfer data from one end device to another across the network. The routed protocol is the Layer 3 datagram that carries the application data in addition to the upper-layer information.
The routing protocol is the protocol used to send updates between the routers about the networks that exist in the organization, thereby allowing the routing process to determine the path of the datagram across the network.
10: Describe the processes used to build and maintain the routing table.
** There are three steps involved in building and maintaining the routing table. These three processes are independent and include:
The routing protocol, which actually sends the information about the routes or networks within the autonomous system, such as RIPv1, IGRP, EIGRP
The routing table, which receives updates from the routing protocol and provides the forwarding process with information on request
The forwarding process, which determines which path to select from the routing table in order to forward a datagram
11: Give a brief explanation of the switching function.
** The switching function does the following:
- Checks the incoming frame for validity
- Checks whether the frame is addressed (at Layer 2) to the router
- Checks whether the frame is within the scope of the framing criteria (too big or too small)
- Checks whether the frame passes CRC
- Strips the Layer 2 header and trailer from the frame and checks the destination address against the cache entries
- Creates the appropriate frame header and trailer (if there is an entry in cache for the destination address) and forwards the frame to the outbound interface queue
12: What information is contained in the fast switching cache?
** If fast switching is enabled, the datagram is then examined again, and an entry is put into a route cache. The entry in this cache consists of the following:
- An IP prefix
- The output interface
- The link-layer header to be used in forwarding the datagram
13: When would you use the command no auto-summary?
** Some routing protocols, such as BGP, RIPv2, and EIGRP, summarize at the network boundary automatically. Summarization within the NIC number boundary must be configured manually, and therefore autosummarization must first be disabled with the no auto-summary command.
14: When does OSPF send updates, and do they contain the entire routing table?
** Each OSPF router refreshes its LSA every 30 minutes. An LSA will be sent earlier if there is an adjacency change.
15: Network convergence is when a network domain has learned about the new network topology after a change has occurred in the domain. What is considered a network change that would require network convergence?
** The accuracy of the table will be affected by how quickly it responds to changes in the network. These changes include the following:
- Learning new networks
- Learning a better path to an existing network
- Learning that a network is no longer available
- Learning an alternative route to a network
16: When would you consider using a static route in your network?
** A static route would be configured for the following reasons:
- Links that have very low bandwidth, such as dialup links
- The administrator needs control over the link
- The link is a backup to the dynamically learned route
- There is only one path to the remote network, such as a stub network
- The router has very limited resources and cannot run a routing protocol
- The administrator needs to control the routing table to allow a classful protocol and a classless routing protocol to populate the routing table
17: When would you consider using a default route in your network?
** Occasions for using a default route include:
- Connecting to the autonomous system from a stub network
- Connecting to the Internet
18: What command is used to configure ODR on a hub router?
** router odr is the only command needed to be configured on the hub router.
19: When would you consider using a floating static route in your network?
** Floating static routes are used when a backup route is required.
20: Describe some of the characteristics of classless routing protocols.
** Classless routing protocols include OSPF, EIGRP, RIPv2, IS-IS, and BGP.
- The characteristics of a classless routing protocol are:
- Router interfaces within the same network can have different subnet masks (VLSM).
- They support the use of classless interdomain routing (CIDR).
- Some routes can be summarized within the major NIC number. This is done manually.
posted by Arivu at
12:22 pm
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