3.1 Components of Routing Table Flashcards
Interpret the components of routing table, including routing protocol code, prefix, network mask, next hop, administrative distance, metric, and gateway of last resort. (24 cards)
How does a router determine the best path for a packet?
It references the IP Routing Table.
The routing table contains destination networks, next hops, and metrics.
List three key fields found in a basic routing table.
- Destination Network
- Outgoing Interface
- Next Hop
Destination Network – Specifies the target network or subnet the router can reach.
Outgoing Interface – Indicates the router’s interface used to forward packets to the destination.
Next Hop – The IP address of the next router in the path to the destination.
Fill in the blank:
The command to check for a static host route in the routing table is ______ ______ ______ ______.
show ip route static
This command displays only manually configured static routes instead of showing all routing table entries.
List three ways routers add routes to their routing tables?
- Connected routes
- Static routes
- Routing protocols
Connected Routes – Automatically added for active, directly assigned interfaces.
Static Routes – Manually set by an administrator for specific paths.
Dynamic Routing Protocols – Learned via protocols like OSPF, EIGRP, and RIP.
What conditions must a Cisco router meet to add a subnet route to its routing table?
- The interface must have an IP address assigned using the ip address command.
- The interface must be operational, meaning both the line status (Layer 1) and protocol status (Layer 2) are up.
For a router to add a directly connected subnet to its routing table, the interface must be both configured and active.
What routing table code represents a static route?
S
The ‘S’ code indicates that the route was manually set rather than learned through a routing protocol.
Which two routing table components are essential for packet forwarding?
- Next-Hop router
- Outgoing interface
Next-Hop Router – The IP address of the next device in the path to the destination.
Outgoing Interface – The router port used to forward the packet.
Where in the routing table output can you find the next-hop router’s IP address?
Under the “via” field in show ip route output.
In routing table entries, the next-hop router is displayed after the “via” keyword. If a route is directly connected, there is no next-hop, and the outgoing interface is listed instead.
In the output of the show ip route command, what does “via” indicate?
The next-hop router’s IP address.
The next hop is the immediate router where packets are forwarded before reaching their destination.
In the routing entry I 10.0.0.0/8 [100/1600] via 172.16.1.200, what is the next-hop router’s IP address?
172.16.1.200
The next-hop router (172.16.1.200) is the immediate device that forwards packets toward the destination network.
What are the three possible types of next-hop values in a routing table?
- IPv4 or IPv6 address (e.g., 10.2.2.5)
- Directly connected interface (e.g., GigabitEthernet0/0)
- Null0 (discard route)
The next-hop field in show ip route can contain a next-hop IP, an exit interface, or Null0 for discarding traffic when a static route is used for summarization.
List three key details displayed in the show ip route command.
- Prefix (Destination Network)
- Subnet Mask
- Routing Protocol Used
These components help the router determine the best path to reach a destination.
What command displays the routing protocol settings and timers?
show ip protocols
This command provides information about active routing protocols, timers, and metrics.
How can you check the Administrative Distance for subnet 172.16.5.0?
Use “show ip route 172.16.5.0”.
This command filters the routing table to display only entries related to that subnet.
True or False:
The Administrative Distance (AD) selects the best path to a destination.
False
AD determines the trustworthiness of a route, not efficiency. A lower AD is preferred over a higher one.
What is the “Gateway of Last Resort”?
A default route used when no specific route exists.
Typically set as 0.0.0.0/0 and points to a default router.
How do you verify if a default route (Gateway of Last Resort) is set?
Use show ip route.
This command reveals whether a 0.0.0.0/0 route exists.
What commands can be used to configure a Gateway of Last Resort?
- ip route 0.0.0.0 0.0.0.0 <next-hop></next-hop>
- ip default-network <network></network>
- ip default-gateway <gateway></gateway>
These commands allow routers to forward packets to unknown networks.
What command displays all known routes on a Cisco router?
show ip route
This command lists static, dynamic, and connected routes along with metrics and next hops.
Fill in the blank:
In the output R 10.0.0.0/8 [90/1] via 172.16.1.200, the prefix is ______.
10.0.0.0
The prefix represents the destination subnet that this route applies to.
Before sending an IP packet, what is the first action a host takes?
It checks whether the destination is on the local subnet.
If the destination is not local, the packet is forwarded to the default gateway.
What is network mask in a routing table?
A value that defines subnet size and separates network from host.
The network mask (e.g., /24 or 255.255.255.0) determines which portion of an IP address identifies the network and which portion is assigned to individual hosts.
In the routing output O 172.16.4.0 [110/2] via 10.10.10.5, FastEthernet0/0, what does 2 represent?
The metric
The metric indicates the best path among multiple routes available for the destination.
List how different routing protocols calculate the metric value.
- RIP – Hop count (number of routers a packet must pass through).
- OSPF – Cost (based on interface bandwidth).
- EIGRP – Composite metric (uses bandwidth, delay, reliability, and load).
The metric value helps the router determine the best path to a destination. Lower metric values indicate a better route.
