Nexus Interview Questions & Answers

Nexus Interview Questions & Answers

1. What is the command is used to verify the “HSRP Active State” on a Nexus 7000 Series Switch?


The command is show hsrp active or show hsrp brief .
Nexux_7K# show hsrp br

Nexus_7K# show hsrp standb br

2. On a Nexus 7018, when trying to perform a ‘no shut’ on Ethernet 1/3, the ERROR: Ethernet1/3: Config not allowed, as first port in the port-grp is dedicated error message is received.


The device thinks that the first port in the port-grp is in dedicated mode instead of shared mode. When the first port of a port-grp is in dedicated mode, the other ports of the port-grp cannot be used.

3. What is vPC and what are its benefits?


Virtual PortChannel (vPC) is a port-channeling concept that extends link aggregation to two separate physical switches.
Benefits of vPC include:
Utilizes all available uplink bandwidth
Allows the creation of resilient Layer 2 topologies based on link aggregation
Eliminates the dependence of Spanning Tree Protocol in Layer 2 access distribution layer(s)
Enables transparent server mobility and server high availability (HA) clusters
Scales available Layer 2 bandwidth
Simplifies network design
Dual-homed servers can operate in active-active mode
Faster convergence upon link failure
Improves convergence time when a single device fails
Reduces capex and opex

4. Why does vPC not block either of the vPC uplinks?


Nexus 7000 has a loop prevention method that drops traffic traversing the peer link (destined for a vPC peer link) when there are no failed vPC ports or links. The rule is simple: if the packet crosses the vPC peer link, it may not go out any port in a vPC even if that vPC does not have the original VLAN.

5. How do I verify the features enabled on Nexus 7000 Series Switch with NX-OS 4.2?


Issue the show feature command in order to verify.
switch-N7K# show feature
Feature Name Instance State
——————– ——– ——–
tacacs 1 enabled
scheduler 1 enabled
isis 2 disabled
isis 3 disabled
isis 4 disabled
ospf 1 enabled
ospf 2 disabled
ospf 3 disabled

switch-N7K# show run | I feature
feature vrrp
feature tacacs+
feature scheduler
feature ospf

6. Is there a tool available for configuration conversion on Cisco 6500 series to the Nexus platform?


Cisco has developed the IOS-NXOS Migration Tool for quick configuration conversion on Cisco 6500 series to the Nexus series OS.

7. How many syslog servers can be added to a Nexus 7000 Series Switch?


The maximum number of syslog servers configured is 3.

8. Is Nexus 7010vPC feature (LACP enabled) compatible with the Cisco ASA etherchannel feature and with ACE 4710 etherchannel?


With respect to vPC, any device that runs the LACP (which is a standard), is compatible with the Nexus 7000, including ASA/ACE.

9. What are orphan ports?


Orphan ports are single attached devices that are not connected via a vPC, but still carry vPC VLANs. In the instance of a peer-link shut or restoration, an orphan port’s connectivity may be bound to the vPC failure or restoration process. Issue the show vpc orphan-ports command in order to identify the impacted VLANs.

10. How many OSPF processes can be run in a virtual device context (VDC)?


There can be up to four (4) instances of OSPFv2 in a VDC.

11. Which Nexus 7000 modules support Fibre Channel over Ethernet (FCoE)?


The Cisco Nexus 7000 Series 32-Port 1 and 10 Gigabit Ethernet Module support FCoE. The part number of the product is N7K-F132XP-15.

12. What is the minimum NX-OS release required to support FCoE in the Nexus 7000 Series Switches?


FCoE is supported on Cisco Nexus 7000 Series systems running Cisco NX-OS Release 5.2 or later.

13. On a Nexus, is the metric-type keyword not available in the “default-information originate” command?


On a Nexus, use a route-map command with a set clause of metric-type type-[½] in order to have the same functionality as in IOS using the default-information originate always metric-type [½] command.
For example:
switch(config)#route-map STAT-OSPF, permit, sequence 10
switch(config-route-map)#match interface ethernet 1/2
switch(config-route-map)#set metric-type {external | internal | type-1 | type-2}

14. How do I redistribute connected routes into an OSPF instance on a Nexus 7010 with a defined metric?


In NX-OS, a route-map is always required when redistributing routes into an OSPF instance, and you will also use this route-map to set the metric. Further, subnet redistribution is by default, so you do not have to add the subnets keyword.
For example:
switch(config)#access-list 101 permit ip <connected network> <wildcard> any
switch(config)#access-list 101 permit ip <connected network> <wildcard> any
switch(config)#access-list 101 permit ip <connected network> <wildcard> any
switch(config)#access-list 101 deny any
Router(config)# route-map direct2ospf permit 10
Router(config-route-map)# match ip address 101
Router(config-route-map)# set metric <100>

Router(config-route-map)# set metric-type type-1
switch(config)#router ospf 1
switch(config-router)#redistribute direct route-map direct2ospf

15. What is the equivalent NX-OS command for the “ip multicast-routing” IOS command, and does the Nexus 7000 support PIM-Sparse mode?


The command is feature pim. In NX-OS, multicast is enabled only after enabling the PIM or PIM6 feature on each router and then enabling PIM or PIM6 sparse mode on each interface that you want to participate in multicast.
For example:

switch(config)#feature pim
switch(config)#interface Vlan[536]switch(config-if)#ip pim sparse-mode
See Cisco Nexus 7000 Series NX-OS Multicast Routing Configuration Guide, Release 5.x for a complete configuration guide.

16. When I issue the “show ip route bgp” command, I see my routes being learned via OSPF and BGP. How can I verify on the NX-OS which one will always be used and which one is a backup?


Here is what is received:
Nexus_7010#show ip route bgp
IP Route Table for VRF “default”
‘*’ denotes best ucast next-hop
‘**’ denotes best mcast next-hop
‘[x/y]’ denotes [preference/metric], ubest/mbest: 1/0
*via, [20/0], 18:53:35, bgp-[AS-Number], internal, tag [Number]via, Vlan116, [110/1043], 18:43:51, ospf-1, intra, ubest/mbest: 1/0
*via, [20/0], 18:53:35, bgp-[AS-Number], internal, tag [Number]via, Vlan116, [110/1041], 18:43:51, ospf-1, intra
By default, BGP selects only a single best path and does not perform load balancing. As a result, the route marked with the * will always be used, unless it goes down, at which point any remaining routes will become the preferred path.

17. How do I avoid receiving the “Failed to process kickstart image. Pre-Upgrade check failed” error message when upgrading the image on a Nexus 7000 Series Switch?


One potential reason for receiving this error message is if the file name specified is not correct.
For example:
switch#install all kickstart bootflash:n7000-sl-kickstart.5.1.1a.bin system
In this example, the file name contains “sl” (lowercase letter l) instead of “s1” (number 1).

18. How can I avoid receiving the “Configuration does not match the port capability” error message when enabling “switchport mode fex-fabric”?


This error message is generated because the port is not FEX capable:

N7K-2(config)#interface ethernet 9/5
N7K-2(config-if)#switchport mode fex-fabric
ERROR: Ethernet9/5: Configuration does not match the port capability
In order to resolve this problem, check the port capabilities by using the show interface ethernet command.
For example:
N7K-2#show interface ethernet 9/5 capabilities
Model: N7K-M132XP-12
Type (SFP capable): 10Gbase-(unknown)
Speed: 10000
Duplex: full
Trunk encap. type: 802.1Q
Channel: yes
Broadcast suppression: percentage(0-100)
Flowcontrol: rx-(off/on),tx-(off/on)
Rate mode: shared
QOS scheduling: rx-(8q2t),tx-(1p7q4t)
CoS rewrite: yes
ToS rewrite: yes
SPAN: yes
UDLD: yes
Link Debounce: yes
Link Debounce Time: yes
MDIX: no
Pvlan Trunk capable: no
Port Group Members: 1,3,5,7
TDR capable: no
FabricPath capable: no
Port mode: Routed,Switched
FEX Fabric: no
dot1Q-tunnel mode: yes
From this output of the show interface ethernet 9/5 capabilities command, you can see FEX Fabric: no. This verifies that the port is not FEX capable. In order to resolve this problem, upgrade the EPLD images to Cisco NX-OS Release 5.1(1) or later.

19. When I issue the “show interface counters errors” command, I see that one of the interfaces is consistently posting errors. What are the FCS-Err and Rcv-Err in the output of the “show interface counters errors” command?


Here is what is received:
Nexus-7000#show interface counters errors

Port Align-Err FCS-Err Xmit-Err Rcv-Err UnderSize OutDiscards
Eth1/1 0 26 0 26 0 0
With FCS-Err and Rcv-Err, it is usually an indication that you are receiving corrupt packets.

20. How do I enable/disable logging link status per port basis on a Nexus 7000 Series Switch?


All interface link status (up/down) messages are logged by default. Link status events can be configured globally or per interface. The interfacecommand enables link status logging messages for a specific interface.
For example:
N7k(config)#interface ethernet x/x
N7k(config-if)#logging event port link-status

21. How do I check the Network Time Protocol (NTP) status on a Nexus 7000 Series Switch?


In order to display the status of the NTP peers, issue the show ntp peer-status command:
switch#show ntp peer-status

Total peers : 1

* – selected for sync, + – peer mode(active),

– – peer mode(passive), = – polled in client mode

remote local st poll reach delay vrf


* 1 64 377 0.00134 default

22. How do I capture the output of the show tech-support details?


Issue the tac-pac bootflash://<filename> command in order to redirect the output of the show tech command to a file, and then gzip the file.
For example:
switch#tac-pac bootflash://showtech.switch1
Issue the copy bootflash://showtech.switch1 tftp://<server IP/<path> command in order to copy the file from bootflash to the TFTP server.
For example:
switch#copy bootflash://showtech.switch1 tftp://<server IP/<path>

23. Can a Nexus 7000 be a DHCP server and can it relay DHCP requests to different DHCP servers per VLAN?


The Nexus 7000 does not support a DHCP server, but it does support DHCP relay. For relay, use the ip dhcp relay address x.x.x.x interface command.
See Cisco Nexus 7000 Series NX-OS Security Configuration Guide, Release 5.x for more information on Dynamic Host Configuration Protocol (DHCP) on a Cisco NX-OS device.

24. How do I implement VTP in a Nexus 7000 Series Switch where VLANs are manually configured?


Cisco does not recommend running VTP in data centers. If someone attaches a switch to the network with a higher revision number without changing the VTP mode from the server, it will override the VLAN configuration on the switch.

25. Is there a best practice for port-channel load balancing between Nexus 1000V Series and Nexus 7000 Series Switches?


There is no recommended best practice for load-balancing between the Nexus 1000V Series and Nexus 7000 Series Switches. You can choose either a flow-based or a source-based model depending on the network’s requirement.

26. During Nexus 7010 upgrade from 5.2.1 to 5.2.3 code, the X-bar module in slot 4 keeps powering off. The %MODULE-2-XBAR_DIAG_FAIL: Xbar 4 reported failure due to Module asic(s) reported sync loss (DevErr is LinkNum). Trying to Resync in device 88 (device error 0x0) error message is received.


This error message corresponds to diagnostic failures on module 2. It could be a bad connection to the X-bar from the linecard, which is results in the linecard being unable to sync. Typically with these errors, the first step is to reseat the module. If that does not resolve the problem, reseat the fabric as well as the module individually.

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