Examkin

IP Connectivity

493 soru

Tüm türler493Çoktan seçmeli250Çoklu seçim113Eşleştirme25Sıralama60Boşluk doldurma22Kısa cevap23
Soru 181Soru →

When a Cisco router processes an ingress IPv4 packet destined for a remote network, it executes a deterministic evaluation sequence to determine the forwarding path and transmit the frame. Place the operational steps in the correct chronological order from packet ingress to egress frame encapsulation.

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Cevap

The correct evaluation sequence begins with extracting the destination IPv4 address, followed by performing Longest Prefix Match lookup in the routing table, evaluating protocol metrics for equal prefix ties, resolving the next-hop IP and egress interface, and finally resolving ARP to rewrite Layer 2 headers for frame transmission.
Router forwarding logic follows a mandatory sequence: packet header inspection, route selection via Longest Prefix Match (LPM), tie-breaking via metric for matching prefix length, identification of exit interface/next-hop IP, and Layer 2 frame encapsulation via ARP lookup.

Adım Adım Çözüm

1
Parse packet header
Destination IPv4 address identified
The router must inspect the Layer 3 header to determine where the packet is destined.
2
Perform Longest Prefix Match (LPM)
Candidate route with most specific subnet mask selected
Longest Prefix Match is the absolute primary rule in IP route selection.
3
Evaluate protocol metric
Single best route or equal-cost paths selected
If identical routes exist within a single protocol source, metric breaks the tie.
4
Determine egress parameters
Next-hop IP and outbound interface bound
The router maps the selected routing entry to its configured exit interface and next hop.
5
Encapsulate and transmit frame
Layer 2 MAC rewrite complete and bits transmitted
Address Resolution Protocol (ARP) supplies the next-hop MAC address to build the new data link layer frame.

Anahtar Kavram

Router Forwarding Decision Logic
Soru 182Soru →

Refer to the following partial output from the show ip route command on a Cisco router:

text
Gateway of last resort is 10.1.1.1 to network 0.0.0.0

D 10.50.0.0/16 [90/307200] via 10.2.2.2, GigabitEthernet0/1
O 10.50.10.0/24 [110/20] via 10.3.3.3, GigabitEthernet0/2
S 10.50.10.64/26 [1/0] via 10.4.4.4, GigabitEthernet0/3
S* 0.0.0.0/0 [1/0] via 10.1.1.1, GigabitEthernet0/0

The router receives an IPv4 packet destined for host 10.50.10.75. Which next-hop IP address will the router choose to forward this packet?

Cevabı ve açıklamayı göster

Cevap: 10.4.4.4

Cevap

The router will select the next-hop IP address 10.4.4.4 associated with the longest prefix match route 10.50.10.64/26.
When a router performs a routing lookup for a packet destination IP, it checks for matching entries in the IP routing table and selects the route with the most specific match (the longest subnet mask). In this case, 10.50.10.75 matches 10.50.0.0/16, 10.50.10.0/24, and 10.50.10.64/26. The /26 prefix is the longest match, so the packet is forwarded via its next hop, 10.4.4.4.

Adım Adım Çözüm

1
Identify all routes in the routing table that match the destination IP address 10.50.10.75.
The IP address 10.50.10.75 matches three specific routes: 10.50.0.0/16, 10.50.10.0/24, and 10.50.10.64/26 (range: 10.50.10.64 to 10.50.10.127), plus the default route 0.0.0.0/0.
Routing lookup matches the destination address against all configured prefixes.
2
Compare the prefix lengths of all matching routes to determine the Longest Prefix Match (LPM).
Prefix lengths are /16, /24, /26, and /0. The longest prefix match is /26 (10.50.10.64/26).
Routers always prioritize the most specific matching route (longest subnet mask / prefix length) regardless of administrative distance or metric.
3
Determine the next-hop IP address associated with the longest matching prefix.
The route 10.50.10.64/26 points to the next hop 10.4.4.4.
The next-hop address specified by the LPM entry is used for packet forwarding.

Anahtar Kavram

Longest Prefix Match (LPM) Rule
Soru 183Soru →

A network technician is configuring an IPv6 static route on a Cisco router. The destination network is 2001:db8:c0ff:50::/642001:\text{db8}:\text{c0ff}:50::/64. The next-hop router's link-local IPv6 address is fe80::a5\text{fe80}::a5, and traffic must exit via the local interface GigabitEthernet0/0/0. What is the exact, complete Cisco IOS command required to configure this fully specified static route with a custom administrative distance of 130?

Aşağıdaki boşlukları doldurun

Enter the complete Cisco IOS command:
Cevabı ve açıklamayı göster

Cevap

ipv6 route 2001:db8:c0ff:50::/64 GigabitEthernet0/0/0 fe80::a5 130
Configuring an IPv6 static route with a link-local next-hop address requires a fully specified route format: 'ipv6 route <destination-prefix/prefix-length> <exit-interface> <link-local-next-hop> [administrative-distance]'. In this scenario, combining the target prefix '2001:db8:c0ff:50::/64', local exit interface 'GigabitEthernet0/0/0', link-local next-hop 'fe80::a5', and administrative distance '130' results in 'ipv6 route 2001:db8:c0ff:50::/64 GigabitEthernet0/0/0 fe80::a5 130'.

Adım Adım Çözüm

1
Identify the base global configuration command and destination prefix.
The static route command begins with 'ipv6 route' followed by the target IPv6 network prefix and prefix length '2001:db8:c0ff:50::/64'.
Cisco IOS requires the keyword 'ipv6 route' followed immediately by the destination network identifier.
2
Identify the requirement for specifying the local exit interface.
Place 'GigabitEthernet0/0/0' after the destination prefix.
Because link-local addresses (fe80::/10) are scope-local and ambiguous across multiple router interfaces, Cisco IOS requires specifying the exit interface whenever a link-local address is used as a next hop.
3
Append the link-local next-hop address and administrative distance.
Add the link-local next-hop IPv6 address 'fe80::a5' followed by the administrative distance integer '130'.
Completes the syntax for a fully specified IPv6 static route while applying the requested custom administrative distance.

Anahtar Kavram

Fully Specified IPv6 Static Route Configuration
Tahmini Süre:1m 30s
Soru 184Soru →

A network administrator needs to configure an IPv6 default static route on a Cisco IOS router pointing to the exit interface GigabitEthernet0/0. Complete the command by specifying the IPv6 default route prefix notation.

Aşağıdaki boşlukları doldurun

ipv6 route GigabitEthernet0/0
Cevabı ve açıklamayı göster

Cevap

The correct prefix notation to complete the IPv6 static default route command is ::/0.
The IPv6 default route prefix is designated as ::/0, which matches all destination networks regardless of prefix length.

Adım Adım Çözüm

1
Identify the IPv6 address representation for a default route.
In IPv6 addressing, all zeros with a prefix length of zero bits is represented using compressed format as ::/0.
The prefix ::/0 matches any IPv6 destination network when no more specific match exists in the routing table.

Anahtar Kavram

IPv6 Default Static Route Syntax
Soru 185Soru →

Refer to the following partial IPv4 routing table output from a Cisco router:

text
Gateway of last resort is 10.10.10.1 to network 0.0.0.0

D 10.150.24.0/26 [90/307200] via 10.1.1.2, 00:15:10, GigabitEthernet0/0
O 10.150.24.0/24 [110/20] via 10.2.2.2, 01:20:45, GigabitEthernet0/1
S 10.150.24.32/28 [1/0] via 10.3.3.2, 02:04:12, GigabitEthernet0/2
S* 0.0.0.0/0 [1/0] via 10.10.10.1, 12:00:00, GigabitEthernet0/3

The router receives an IPv4 packet destined for host 10.150.24.4010.150.24.40. Which two statements accurately describe how the router makes its forwarding decision for this packet?

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: The packet is forwarded out interface GigabitEthernet0/2 because 10.150.24.32/28 has the longest prefix match for the destination address.; The router compares subnet mask lengths prior to evaluating Administrative Distance values across candidate routes.

Cevap

The router forwards the packet out interface GigabitEthernet0/2 because 10.150.24.32/28 represents the longest matching prefix for host 10.150.24.40, and prefix length evaluation strictly precedes Administrative Distance comparison.
When a router receives a packet, it searches its routing table for all matching prefixes and selects the route with the longest prefix length (most specific mask). The destination address 10.150.24.40 matches 10.150.24.32/28 (/28), 10.150.24.0/26 (/26), 10.150.24.0/24 (/24), and 0.0.0.0/0 (/0). Since /28 is the longest mask, the route via GigabitEthernet0/2 is chosen. The router checks prefix length before Administrative Distance or metric values.

Adım Adım Çözüm

1
Determine which routes match the destination IP address 10.150.24.40.
Matching routes are 10.150.24.0/24, 10.150.24.0/26, 10.150.24.32/28, and default route 0.0.0.0/0.
The destination address 10.150.24.40 falls into the address ranges of all four listed routes.
2
Apply the Longest Prefix Match (LPM) rule across all matching routes.
10.150.24.32/28 has a 28-bit mask length, which is the most specific match compared to /26, /24, and /0.
Routers always prefer the route with the highest number of matching leading network bits (longest prefix).
3
Determine the egress interface and next-hop for the winning route 10.150.24.32/28.
The packet will be forwarded to next-hop 10.3.3.2 via interface GigabitEthernet0/2.
The routing table explicitly points the static route 10.150.24.32/28 out interface GigabitEthernet0/2.

Anahtar Kavram

Router Forwarding Decision Logic and Longest Prefix Match precedence
Soru 186Soru →

An administrator reviews the following IPv4 routing table snippet on a Cisco router:

text
Gateway of last resort is 172.20.10.1 to network 0.0.0.0

B 10.100.0.0/16 [200/0] via 172.20.10.2, 04:12:30
O IA 10.100.16.0/20 [110/35] via 192.168.20.2, 01:05:18, GigabitEthernet0/1
D 10.100.20.0/22 [90/156160] via 192.168.30.2, 00:18:42, GigabitEthernet0/2
C 192.168.20.0/24 is directly connected, GigabitEthernet0/1
L 192.168.20.1/32 is directly connected, GigabitEthernet0/1

A packet arrives at the router addressed to 10.100.21.5010.100.21.50. Which TWO statements correctly describe how the routing table components are evaluated to forward this packet? (Select TWO.)

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: The router selects the route for 10.100.20.0/22 because it provides the longest prefix match (/22) for the destination IP address.; The routing entry for 10.100.20.0/22 indicates an administrative distance of 90 and a metric of 156160.

Cevap

The router selects the route for 10.100.20.0/22 based on the longest prefix match rule, and the routing entry defines an administrative distance of 90 with a metric of 156160.
When evaluating incoming packets for forwarding, Cisco routers determine all matching routes and choose the route with the longest subnet mask (most specific prefix). The address 10.100.21.50 matches three entries, but 10.100.20.0/22 has the longest prefix length (/22). Furthermore, Cisco routing tables present protocol metadata in the bracketed structure [Administrative Distance / Metric], which identifies an administrative distance of 90 and a metric value of 156160 for the EIGRP route.

Adım Adım Çözüm

1
Determine which routing table entries match the destination IP address 10.100.21.50.
The destination address matches 10.100.0.0/16, 10.100.16.0/20, and 10.100.20.0/22.
10.100.21.50 falls within the host ranges of all three subnets.
2
Apply the Longest Prefix Match (LPM) forwarding rule.
Select 10.100.20.0/22 because /22 has the longest subnet mask length.
Cisco routers always prefer the route with the most specific prefix length first before evaluating administrative distance or metric.
3
Parse the bracketed components [90/156160] for the selected route.
Administrative Distance is 90 and Metric is 156160.
Cisco output displays bracketed metrics formatted as [Administrative Distance / Metric].

Anahtar Kavram

Routing Table Component Interpretation and Longest Prefix Match Selection
Soru 187Soru →

A network administrator needs to manually configure a backup floating static route on a Cisco IOS router. Arrange the following syntax elements in the correct sequential order from left to right to construct a valid Cisco IOS floating static route command.

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Cevap

The correct sequence to construct the command is: ip route 172.16.1.0 255.255.255.0 10.1.1.2 130.
The correct order follows the standard Cisco IOS static route syntax: 'ip route <destination-prefix> <subnet-mask> {ip-address | exit-interface} [distance]'. The command starts with 'ip route', followed by the target destination network (172.16.1.0), the subnet mask (255.255.255.0), the next-hop address (10.1.1.2), and finally the optional Administrative Distance value (130).

Adım Adım Çözüm

1
Begin with the global configuration command keyword.
Specifies 'ip route' at the beginning of the command string.
Cisco IOS requires the 'ip route' command keyword to define a static routing entry.
2
Append the destination network address followed by its subnet mask.
Adds '172.16.1.0 255.255.255.0'.
The router needs the target IP subnet prefix and corresponding subnet mask to evaluate match length in the routing table.
3
Specify the next-hop IP address or local exit interface.
Adds '10.1.1.2'.
Defines the forwarding destination or gateway to reach the target network.
4
Append the optional Administrative Distance value at the end.
Adds '130'.
Assigning an Administrative Distance higher than the primary route (e.g., OSPF AD 110) creates a floating static route that remains inactive until the primary route drops.

Anahtar Kavram

Cisco IOS IPv4 static route CLI syntax structure and floating static route parameter placement.
Soru 188Soru →

A Cisco router receives an IPv4 packet destined for a remote host and evaluates its routing table containing multiple routes from different sources. Place the steps of the router's forwarding decision logic in the correct order from first to last.

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Cevap

The correct sequence of router forwarding decision logic from first to last is: 1) Select the route with the longest prefix match; 2) Compare Administrative Distance if prefix lengths are identical; 3) Compare metric values if AD and prefix lengths are identical; 4) Forward the packet using the selected route's exit interface and next hop.
When a Cisco router makes a forwarding decision, it follows a strict hierarchical evaluation sequence. First, it identifies all routes in the routing table that match the destination IPv4 address and selects the route with the longest prefix match (most specific subnet mask). Second, if there are multiple matching routes with identical prefix lengths, it evaluates Administrative Distance (AD) to pick the route from the most trustworthy routing protocol. Third, if multiple routes share identical prefix lengths and AD values, it compares the metric (path cost) to choose the lowest metric route. Finally, once the single best route is determined, the router forwards the packet out the associated exit interface.

Adım Adım Çözüm

1
Evaluate Longest Prefix Match (LPM)
The router identifies all routes matching the destination IP address and prioritizes the route with the longest prefix length (most specific subnet mask).
LPM always takes absolute precedence over Administrative Distance and Metric.
2
Compare Administrative Distance (AD)
If multiple routes have the exact same prefix length, the router selects the route from the routing source with the lowest AD.
Administrative Distance measures the believability and trustworthiness of the routing source.
3
Compare Metric
If AD and prefix length are identical (e.g., multiple routes learned via the same dynamic routing protocol), the route with the lowest metric is selected.
Metric measures path cost within a single routing protocol.
4
Forward the Packet
The router encapsulates the packet and sends it via the selected route's exit interface and next-hop IP address.
Once the best route determination is complete, the data plane handles packet transmission.

Anahtar Kavram

Router Forwarding Decision Logic Precedence (Longest Prefix Match > Administrative Distance > Metric)
Soru 189Soru →

In a Cisco IOS IPv4 routing table displayed via the `show ip route` command, prefix source codes identify how routes were populated. Match each routing table source code on the left with its corresponding route origin and default administrative distance on the right.

Soldaki öğeye tıklayın, sonra eşleşen sağdaki öğeye tıklayın

Öğeler

Source Code C
Source Code S
Source Code O
Source Code D

Eşleşmeler

Cevabı ve açıklamayı göster

Cevap

Source Code C matches Directly connected network (Default AD: 0); Source Code S matches Statically configured route (Default AD: 1); Source Code O matches OSPF dynamic routing protocol (Default AD: 110); Source Code D matches EIGRP dynamic routing protocol (Default AD: 90).
Each routing table code corresponds strictly to a routing source and its trust rating (administrative distance). Code C represents connected interfaces (AD 0), code S represents static routes (AD 1), code O represents OSPF routes (AD 110), and code D represents internal EIGRP routes (AD 90).

Adım Adım Çözüm

1
Identify the meaning of source code C in Cisco IOS routing output.
Code C stands for Connected networks, assigned an Administrative Distance of 0.
Directly connected interfaces are the most trusted route source.
2
Identify the meaning of source code S in Cisco IOS routing output.
Code S stands for Static routes, assigned a default Administrative Distance of 1.
Static routes are manually created by network administrators.
3
Identify the meaning of source code O in Cisco IOS routing output.
Code O stands for Open Shortest Path First (OSPF), assigned a default Administrative Distance of 110.
Cisco IOS assigns OSPF an AD of 110.
4
Identify the meaning of source code D in Cisco IOS routing output.
Code D stands for EIGRP (derived from the Diffusing Update Algorithm - DUAL), assigned a default internal Administrative Distance of 90.
Letter D is used for EIGRP because E uses Exterior Gateway Protocol in older routing tables.

Anahtar Kavram

Routing Table Source Codes and Administrative Distance
Soru 190Soru →

Refer to the following routing table output from a Cisco router:

Codes: C - connected, S - static, R - RIP, D - EIGRP, O - OSPF

Gateway of last resort is not set

S 172.20.0.0/16 [1/0] via 10.0.0.1, GigabitEthernet0/0
D 172.20.100.0/24 [90/2578560] via 10.0.0.2, GigabitEthernet0/1
O 172.20.100.32/27 [110/20] via 10.0.0.3, GigabitEthernet0/2
S 172.20.100.40/30 [1/0] via 10.0.0.4, GigabitEthernet0/3

Which next-hop IP address and exit interface will the router select to forward an ingress IPv4 packet destined for 172.20.100.45?

Cevabı ve açıklamayı göster

Cevap: 10.0.0.3 via GigabitEthernet0/2 because 172.20.100.32/27 is the longest matching prefix for the destination address.

Cevap

The router forwards the packet to next-hop 10.0.0.3 out interface GigabitEthernet0/2 because 172.20.100.32/27 is the longest matching prefix that encompasses destination 172.20.100.45.
When a router receives a packet, it compares the destination IPv4 address against all routes in the Routing Information Base (RIB). Destination 172.20.100.45 matches three routes: 172.20.0.0/16, 172.20.100.0/24, and 172.20.100.32/27. The longest matching prefix is 172.20.100.32/27 because 27 bits is the most specific mask matching the target IP. Therefore, the router forwards the packet to next-hop 10.0.0.3 out interface GigabitEthernet0/2.

Adım Adım Çözüm

1
Determine which routing table prefixes encompass the destination IP address 172.20.100.45.
The prefixes 172.20.0.0/16, 172.20.100.0/24, and 172.20.100.32/27 match destination 172.20.100.45. The prefix 172.20.100.40/30 covers range .40 to .43 and does NOT match .45.
Routing lookup requires identifying all routes whose network mask bits match the destination address.
2
Compare the prefix lengths of all valid candidate routes.
The prefix length /27 is more specific (longer) than /24 and /16.
The router forwarding decision engine strictly follows the Longest Prefix Match (LPM) logic before considering Administrative Distance or Metric.
3
Identify the exit interface and next-hop IP associated with the longest prefix match.
The route entry 172.20.100.32/27 points to next-hop 10.0.0.3 via interface GigabitEthernet0/2.
The candidate route with the longest matching prefix determines the forwarding path.

Anahtar Kavram

Router Forwarding Decision Logic and Longest Prefix Match (LPM)
Soru 191Soru →

A network administrator is configuring a floating static route on router R1 to reach the destination prefix 2001:db8:acad:10::/642001:\text{db8}:\text{acad}:10::/64. The primary path to this network is currently learned via OSPFv3 with an Administrative Distance of 110. The administrator wants to configure the backup static route using the next-hop neighbor's link-local IPv6 address fe80::2fe80::2 across R1's local interface GigabitEthernet0/1. Which command must be entered on R1 to correctly configure this floating static route?

Cevabı ve açıklamayı göster

Cevap: ipv6 route 2001:db8:acad:10::/64 GigabitEthernet0/1 fe80::2 120

Cevap

The command 'ipv6 route 2001:db8:acad:10::/64 GigabitEthernet0/1 fe80::2 120' is the correct configuration.
The option specifying 'ipv6 route 2001:db8:acad:10::/64 GigabitEthernet0/1 fe80::2 120' uses the valid Cisco IOS syntax for a fully specified static route using a link-local next hop. The local exit interface GigabitEthernet0/1 resolves link-local address ambiguity, and an Administrative Distance of 120 ensures the route functions correctly as a floating static backup to the active OSPFv3 route (AD 110).

Adım Adım Çözüm

1
Identify the mandatory components of an IPv6 static route using a link-local address.
Because IPv6 link-local addresses (fe80::/10) are non-routable outside their local link, Cisco IOS requires both the local exit interface and the link-local next-hop address (fully specified static route).
Without specifying the exit interface, the router cannot determine which local segment contains the target fe80::2 address.
2
Determine the required Administrative Distance for a floating static route.
The primary route is OSPFv3 with AD = 110. The floating static route AD must be greater than 110 (e.g., 120).
Setting an AD higher than the primary routing protocol ensures the static route remains inactive in the routing table until the primary OSPFv3 route fails.
3
Verify Cisco IOS syntax order.
The syntax structure is 'ipv6 route <prefix/length> <exit-interface> <link-local-address> [administrative-distance]'.
The correct command syntax specifies interface GigabitEthernet0/1 followed by next-hop fe80::2 and AD 120.

Anahtar Kavram

Fully Specified IPv6 Static Route and Floating Static Route AD Configuration
Soru 192Soru →

A network technician is configuring an IPv6 static route on a router to reach network 2001:DB8:5000:10::/642001:\text{DB8}:\text{5000}:10::/64. The technician intends to use the neighbor's link-local address FE80::2\text{FE80}::2 as the next hop. Which Cisco IOS command correctly configures this route using local interface GigabitEthernet0/1?

Cevabı ve açıklamayı göster

Cevap: ipv6 route 2001:DB8:5000:10::/64 GigabitEthernet0/1 FE80::2

Cevap

The command 'ipv6 route 2001:DB8:5000:10::/64 GigabitEthernet0/1 FE80::2' correctly configures the static route.
In Cisco IOS, a fully specified static route using a link-local next-hop address MUST explicitly specify the local exit interface (e.g., GigabitEthernet0/1) prior to the link-local address. This resolves ambiguity because link-local addresses exist on every IPv6-enabled interface.

Adım Adım Çözüm

1
Identify the proper command syntax for IPv6 static routing
Begin with 'ipv6 route' followed by the target destination prefix and length.
Cisco IOS requires 'ipv6 route' for configuring static IPv6 prefixes.
2
Determine interface and next-hop parameter rules for link-local addresses
Include the local exit interface GigabitEthernet0/1 before the next-hop link-local address FE80::2\text{FE80}::2.
Because link-local addresses belong to the FE80::/10\text{FE80}::/10 block and are non-routable outside their local segment, the router must know which exit interface to use to reach the next hop.

Anahtar Kavram

IPv6 Static Route Link-Local Next-Hop Syntax
Soru 193Soru →

An engineer is configuring a static route on a Cisco router to reach the destination subnet 2001:db8:a100:12::/642001:\text{db8}:\text{a100}:12::/64 using the neighbor link-local address fe80::fe22:1\text{fe80}::\text{fe22}:1 via local interface GigabitEthernet0/1\text{GigabitEthernet0/1}. Complete the Cisco IOS configuration command by filling in the missing parameters in order.

Aşağıdaki boşlukları doldurun

ipv6 route 2001:db8:a100:12::/64
Cevabı ve açıklamayı göster

Cevap

The complete command is: ipv6 route 2001:db8:a100:12::/64 GigabitEthernet0/1 fe80::fe22:1
In Cisco IOS IPv6 static routing, when a link-local address is designated as the next hop, the command must explicitly include the local exit interface preceding the link-local address. Therefore, the first parameter must specify the interface (GigabitEthernet0/1) and the second parameter must specify the link-local address (fe80::fe22:1).

Adım Adım Çözüm

1
Identify the standard Cisco IOS IPv6 static route command structure for link-local next hops.
The command syntax is: ipv6 route <destination-prefix/prefix-length> <exit-interface> <link-local-next-hop>.
Cisco IOS requires specifying the local exit interface when using an IPv6 link-local address as a next hop because link-local addresses are unique only within the scope of a single link.
2
Fill in the required exit interface parameter for the first blank.
blank_1 is GigabitEthernet0/1 (or acceptable interface abbreviation such as gi0/1 or g0/1).
The exit interface specifies which local link to use to resolve the link-local address.
3
Fill in the next-hop IPv6 link-local address for the second blank.
blank_2 is fe80::fe22:1.
The next-hop link-local address follows the exit interface parameter in a fully specified IPv6 static route.

Anahtar Kavram

IPv6 Fully Specified Static Route
Tahmini Süre:1m 15s
Soru 194Soru →

An engineer is troubleshooting IPv4 packet forwarding on a Cisco IOS-XE router. The router receives a packet with a destination IP address of 172.16.100.70. Refer to the routing table output below:

text
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

Gateway of last resort is 10.0.0.1 to network 0.0.0.0

S* 0.0.0.0/0 [1/0] via 10.0.0.1
S 172.16.100.0/24 [1/0] via 10.1.1.1
O 172.16.100.64/27 [110/50] via 10.2.2.2
D 172.16.100.64/28 [90/2170112] via 10.3.3.3
C 172.16.100.64/30 is directly connected, GigabitEthernet0/0/0

Which next-hop IP address or outgoing interface will the router select to forward this packet?

Cevabı ve açıklamayı göster

Cevap: 10.3.3.3

Cevap

The router will forward the packet to next-hop IP address 10.3.3.3.
The router follows the Longest Prefix Match (LPM) algorithm for packet forwarding. For destination 172.16.100.70, the matching routes in the table are 0.0.0.0/0, 172.16.100.0/24, 172.16.100.64/27 (range 172.16.100.64–172.16.100.95), and 172.16.100.64/28 (range 172.16.100.64–172.16.100.79). Among these valid matches, /28 is the most specific mask (longest prefix length). Administrative Distance and metric are only compared when two routes have the exact same prefix length. Therefore, the router chooses the /28 route with next-hop 10.3.3.3.

Adım Adım Çözüm

1
Evaluate all candidate routes in the routing table that encompass destination IP address 172.16.100.70.
The candidate matching routes are 0.0.0.0/0, 172.16.100.0/24, 172.16.100.64/27 (range .64-.95), and 172.16.100.64/28 (range .64-.79). The directly connected 172.16.100.64/30 route covers .64-.67, so it does not match.
Before comparing administrative distance or metric, a router must identify all valid matching prefixes.
2
Apply the Longest Prefix Match (LPM) rule to select the best matching route.
Comparing the prefix lengths of matching routes: /0 < /24 < /27 < /28. The route 172.16.100.64/28 is the longest matching prefix (28 bits).
Cisco routers always prefer the most specific matching prefix (/28 over /27, /24, or /0), regardless of Administrative Distance or routing protocol metric.
3
Identify the next-hop address associated with the winning prefix 172.16.100.64/28.
The route entry for 172.16.100.64/28 specifies 'via 10.3.3.3'.
Packet forwarding uses the next-hop specified by the specific prefix selected by the LPM decision process.

Anahtar Kavram

Longest Prefix Match (LPM) Rule in Cisco IPv4 Forwarding Logic
Soru 195Soru →

An engineer is troubleshooting IPv4 packet forwarding on a Cisco router. The router receives a packet with a destination IP address of 172.28.64.99172.28.64.99. The active routing table contains the following entries:

text
S 172.28.0.0/16 [1/0] via 10.1.1.1
O 172.28.64.0/20 [110/20] via 10.2.2.2
D 172.28.64.64/26 [90/307200] via 10.3.3.3
B 172.28.64.96/28 [20/0] via 10.4.4.4

Which next-hop IP address will the router use to forward the packet, and what is the primary routing logic behind this decision?

Cevabı ve açıklamayı göster

Cevap: Next-hop 10.4.4.4, because 172.28.64.96/28 provides the longest prefix match for destination 172.28.64.99.

Cevap

The router forwards the packet to next-hop 10.4.4.4 because 172.28.64.96/28 provides the longest prefix match for the destination address 172.28.64.99.
When a router makes a packet forwarding decision, it compares the destination IP address against all routes in the routing table and selects the route with the most specific match (the longest subnet mask length / prefix length). Destination 172.28.64.99 falls into 172.28.64.96/28 (range 172.28.64.96 - 172.28.64.111). Because /28 is the longest matching mask (28 bits), it takes absolute priority over the /26, /20, and /16 matches, directing traffic to next-hop 10.4.4.4.

Adım Adım Çözüm

1
Determine which subnets match the destination IP address 172.28.64.99.
All four routes cover the destination address: 172.28.0.0/16 (172.28.0.0-172.28.255.255), 172.28.64.0/20 (172.28.64.0-172.28.79.255), 172.28.64.64/26 (172.28.64.64-172.28.64.127), and 172.28.64.96/28 (172.28.64.96-172.28.64.111).
Before comparing routing attributes, the router identifies candidate routes whose subnet ranges contain the target IP.
2
Apply the Longest Prefix Match (LPM) rule.
The prefix 172.28.64.96/28 has a mask length of 28 bits, which is greater than /26, /20, or /16.
Routers always prefer the most specific route (longest subnet mask / longest matching prefix) regardless of administrative distance or metric.
3
Identify the next-hop IP associated with the winning route.
The route 172.28.64.96/28 specifies next-hop 10.4.4.4.
The packet is forwarded to the next-hop IP corresponding to the most specific matching prefix entry.

Anahtar Kavram

Longest Prefix Match (LPM) in IP Routing Forwarding Decisions
Soru 196Soru →

An engineer is configuring a secondary backup route on core router R1 to reach remote subnet 2001:db8:89ab:2000::/562001:\text{db8}:89\text{ab}:2000::/56 through neighboring router R2. The primary route is learned dynamically via OSPFv3 with an Administrative Distance of 110110. The interconnecting segment between R1 and R2 uses GigabitEthernet0/0/1. R2's interface on this link uses the link-local address fe80::211:22ff:fe33:4455\text{fe80}::211:22\text{ff}:\text{fe33}:4455. Which Cisco IOS command must be configured on R1 to create a valid floating static route with an Administrative Distance of 130130 using R2's link-local address?

Cevabı ve açıklamayı göster

Cevap: ipv6 route 2001:db8:89ab:2000::/56 GigabitEthernet0/0/1 fe80::211:22ff:fe33:4455 130

Cevap

The command 'ipv6 route 2001:db8:89ab:2000::/56 GigabitEthernet0/0/1 fe80::211:22ff:fe33:4455 130' correctly specifies both the exit interface and link-local next-hop address with an Administrative Distance of 130.
When configuring an IPv6 static route using a link-local next-hop address (fe80::/10\text{fe80}::/10), Cisco IOS strictly mandates a fully specified route. This format includes the local exit interface followed by the link-local address of the adjacent router. Appending the value 130 at the end of the syntax correctly sets the Administrative Distance higher than OSPFv3 (110), successfully forming a floating static route.

Adım Adım Çözüm

1
Identify the mandatory components of an IPv6 static route using a link-local address as the next hop.
Because link-local addresses (fe80::/10\text{fe80}::/10) are shared across multiple local links, Cisco IOS requires a fully specified route syntax: 'ipv6 route <prefix/mask> <exit-interface> <link-local-next-hop> [AD]'.
Without the local exit interface, the router cannot determine which physical or logical link to use to reach the target link-local address.
2
Verify Administrative Distance manipulation for floating static route capability.
The primary path is learned via OSPFv3 with AD = 110110. Setting the static route AD to 130130 ensures it remains inactive in the IPv6 routing table until the primary OSPFv3 route disappears.
Floating static routes require an Administrative Distance higher than the active primary routing protocol.
3
Validate the exact command string structure.
The target prefix is 2001:db8:89ab:2000::/562001:\text{db8}:89\text{ab}:2000::/56, the local exit interface is GigabitEthernet0/0/1, the next-hop link-local address is fe80::211:22ff:fe33:4455\text{fe80}::211:22\text{ff}:\text{fe33}:4455, and the metric parameter is 130.
This matches the exact fully specified static route configuration requirements in Cisco IOS.

Anahtar Kavram

Fully Specified IPv6 Static Routes and Link-Local Next-Hop Requirements
Soru 197Soru →

A network engineer is configuring static routes on a Cisco IOS router to establish connectivity across an enterprise IPv6 infrastructure. Which two statements correctly describe valid IPv6 static route configuration syntax and operational requirements on Cisco IOS?

Geçerli olan tümünü seçin

Cevabı ve açıklamayı göster

Cevap: When specifying a link-local IPv6 address as the next-hop, the local exit interface must also be explicitly specified in the static route command.; A floating static IPv6 route is configured by manually assigning an administrative distance that is higher than the administrative distance of the primary route.

Cevap

The two correct statements are: specifying a link-local next-hop address requires defining the local exit interface in the command, and configuring a floating static IPv6 route requires setting an administrative distance higher than that of the primary route.
The statement specifying that a link-local next-hop requires the local exit interface is correct because link-local addresses are non-unique across different interface links. The statement describing floating static routes is correct because setting an administrative distance higher than the active dynamic protocol or primary static route keeps the backup route inactive until the primary route fails.

Adım Adım Çözüm

1
Analyze link-local address scoping rules in Cisco IOS static routing.
Link-local addresses (FE80::/10) are link-dependent and non-routable beyond their local segment. Consequently, Cisco IOS requires specifying the egress interface when using a link-local next-hop address.
Without specifying the egress interface, the router cannot determine which local link segment to transmit packets to reach the FE80:: next-hop.
2
Evaluate the administrative distance mechanism for floating static routes.
A floating static route uses a artificially high administrative distance (e.g., AD of 130 backing up OSPF with AD of 110).
The router installs the route into the IPv6 RIB only if lower AD routes for the destination prefix become unavailable.
3
Verify EUI-64 generation rules and global unicast next-hop syntax options.
EUI-64 requires both FFFE insertion and flipping the 7th bit. Global unicast next-hop static routes can be configured recursively without defining an egress interface.
Global unicast addresses are globally unique and can be resolved recursively via the routing table.

Anahtar Kavram

IPv6 Static Routing Syntax and Next-Hop Resolution
Soru 198Soru →

An network engineer is analyzing various IPv4 routing table entries on a Cisco IOS-XE router. Match each routing table code or bracketed component on the left with its correct operational description on the right.

Soldaki öğeye tıklayın, sonra eşleşen sağdaki öğeye tıklayın

Öğeler

Bracketed notation [120/4] in an entry starting with 'R'
Bracketed notation [170/2578560] in an entry starting with 'D EX'
Prefix source code and symbol 'S*'
Prefix source code 'C'

Eşleşmeler

Cevabı ve açıklamayı göster

Cevap

Bracketed notation [120/4] matches the RIP route description with AD 120 and metric 4. Bracketed notation [170/2578560] matches the External EIGRP route with AD 170 and composite metric. Code 'S*' matches the static candidate default route. Code 'C' matches the directly connected network with AD 0.
Each matching pair correctly identifies the Cisco IOS routing table syntax: bracketed notation [AD/Metric], protocol codes ('C' for connected, 'S' for static, 'D EX' for external EIGRP, 'R' for RIP), and special flags such as '*' for candidate default routes.

Adım Adım Çözüm

1
Analyze bracketed notation format [AD/Metric]
Identify that the first integer inside brackets is Administrative Distance (trustworthiness) and the second integer is the routing protocol metric (cost).
Cisco IOS routing tables consistently structure route preference metrics as [Administrative Distance / Metric].
2
Evaluate protocol code 'R' and bracket [120/4]
Match with RIP protocol attributes (AD 120, hop count metric 4).
RIP routes use AD 120 and measure metric in hop counts.
3
Evaluate protocol code 'D EX' and bracket [170/2578560]
Match with External EIGRP route attributes.
Internal EIGRP uses AD 90, but external redistributed EIGRP routes ('D EX') use AD 170 and 32-bit composite metric values.
4
Evaluate static default indicator 'S*'
Match with static candidate default route.
'S' stands for static and '*' designates candidate default.
5
Evaluate connected code 'C'
Match with directly connected interface route (AD 0).
'C' represents connected routes directly assigned to router interfaces.

Anahtar Kavram

Routing Table Components and Administrative Distance
Tahmini Süre:2m 0s
Soru 199Soru →

A Cisco router receives an IPv4 packet destined for a remote host. Place the sequential steps of the router's forwarding decision logic in the correct order from first to last.

Öğeleri doğru sıraya koymak için sürükleyin

Cevabı ve açıklamayı göster

Cevap

The correct sequence begins with extracting the packet's destination IP address, applying Longest Prefix Match to identify candidate routes, comparing Administrative Distance for equal-length prefix ties, comparing metric/cost for intra-protocol ties, and completing Layer 2 encapsulation for egress transmission.
When forwarding an IP packet, a Cisco router follows a precise hierarchy: it extracts the destination address, evaluates all matching routing table entries to find the Longest Prefix Match (most specific subnet mask), breaks ties between different routing protocols using Administrative Distance (lowest wins), breaks ties within the same protocol using Metric/Cost (lowest wins), and finally resolves the Layer 2 next-hop rewrite for frame transmission.

Adım Adım Çözüm

1
Extract Destination IPv4 Address
The destination IP address is identified from the incoming IPv4 packet header.
The destination address is required to query the routing table.
2
Apply Longest Prefix Match (LPM)
Routes with the longest/most specific matching prefix length (subnet mask) are isolated.
LPM is the primary rule of IP routing decision logic and overrides Administrative Distance and Metric.
3
Evaluate Administrative Distance (AD)
If candidate routes have identical prefix lengths, the route with the lowest AD is selected.
AD determines the believability of different routing sources.
4
Evaluate Protocol Metric / Cost
If candidate routes are from the same routing protocol and share equal prefix lengths, the path with the lowest metric is chosen.
Metric measures path efficiency within a single routing protocol.
5
Encapsulate and Forward Frame
The router looks up the next-hop IP in the ARP table, constructs a new Layer 2 header, and sends the frame out the exit interface.
Layer 2 rewrite completes the packet forwarding action at the data plane.

Anahtar Kavram

Router Forwarding Decision Logic Sequence
Soru 200Soru →

Refer to the following partial IPv4 routing table output from a Cisco router:

text
Codes: C - connected, S - static, R - RIP, D - EIGRP, O - OSPF, B - BGP

S 192.168.1.0/24 [1/0] via 10.0.0.3, GigabitEthernet0/0/3
D 192.168.1.128/25 [90/307200] via 10.0.0.2, GigabitEthernet0/0/2
O 192.168.1.128/26 [110/20] via 10.0.0.1, GigabitEthernet0/0/1
B 192.168.1.136/29 [20/0] via 10.0.0.4, GigabitEthernet0/0/4

The router receives a packet destined for host IPv4 address 192.168.1.138. Which next-hop IPv address and exit interface will the router select to forward this packet?

Cevabı ve açıklamayı göster

Cevap: 10.0.0.4 via GigabitEthernet0/0/4, because the /29 prefix provides the longest prefix match for the destination IP address.

Cevap

10.0.0.4 via GigabitEthernet0/0/4, because the /29 prefix provides the longest prefix match for the destination IP address.
When a router receives a packet, it compares the destination IP against all entries in its routing table. The fundamental rule for packet forwarding is Longest Prefix Match (LPM). Among all matching routes for 192.168.1.138, the route 192.168.1.136/29 has the longest subnet mask (/29 vs /26, /25, /24). Therefore, administrative distance and metrics are ignored, and the router selects next-hop 10.0.0.4 via GigabitEthernet0/0/4.

Adım Adım Çözüm

1
Identify all matching routes for destination IP 192.168.1.138 in the routing table.
Routes 192.168.1.0/24, 192.168.1.128/25, 192.168.1.128/26, and 192.168.1.136/29 all encompass 192.168.1.138.
Before comparing routing metrics or administrative distance, candidate matching routes must be identified.
2
Compare the prefix lengths (subnet masks) of all matching routes.
The prefix lengths are /24, /25, /26, and /29. /29 is the longest (most specific) match.
Cisco routers use the Longest Prefix Match (LPM) rule as the primary decision criterion when selecting a route from the routing table to forward a packet.
3
Determine the next-hop IP and exit interface associated with the longest prefix match route.
The route for 192.168.1.136/29 points to next-hop 10.0.0.4 out exit interface GigabitEthernet0/0/4.
The router forwards the packet to the next-hop specified by the winning route.

Anahtar Kavram

Router Forwarding Decision Logic and Longest Prefix Match (LPM)
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