NX-OS uses a modular architecture based on Linux with integrated support for routing protocols, virtualization, and high availability features like Graceful Restart. Key components that enable high availability include the HA Manager, PSS database, and separation of control and data planes to allow non-stop forwarding during process restarts or upgrades.

1. NX-OS: High Availability
NX-OS
SAN-OS
IOS

2. NX-OS modular architecture
Linux Kernel
BGP
OSPF
PIM
TCP/UDP
IPv6
STP
HSRP
LACP
etc
HA Manager
Restart process!
NX7K Data Plane
PSS
Data plane streams
 NX-OS services checkpoint their
runtime state to the PSS for
recovery in the event of a failure
 HA manager includes system manager (just like init process of
Linux), message transaction service ( an Inter Process
Communication ) and Persistent Storage Space (a relation
database of last known state e.g. checkpoint of a process).
N7010B-Dist# show system internal ?
mts MTS statistics
pss Display pss information
sysmgr Internal state of System Manager

3. NX-OS : High Availability
www.silantia.com3
Highly granular modularity in software components
Provides better fault isolation and control
Provides streamlined feature sets and resource usage
Granular in-service software upgrades
Provides better flexibility in upgrades and minimizes
service interruption
Control-Plane / Data-plane functional separation
Non-Stop Forwarding for each of the 3 fundamental
technologies
Helps minimize data forwarding disruption
Integrated Virtualization support for L2 and L3
Better manageability in complex environments
Licensing
Provides flexibility in deployments and growth, Most of the
feature has its own license.

4. NX-OS modular architecture
www.silantia.com4
 Message transaction service: A Interprocess communication
channel
 Persistence Storage Space: A relational databases which stores
health and state of the process in case process fails last state of
process can be queried from PSS.
 System manager Initializes system processes.
 Each VDC has its on HA policy that can be configured while
defining the VDC.
N7010A-Dist(config)# vdc N7010A-Core
N7010A-Dist(config-vdc)# show vdc N7010A-Core detail
vdc id: 2
vdc name: N7010A-Core
vdc state: active
vdc mac address: 00:26:98:07:ea:c2
vdc ha policy: RESTART
vdc dual-sup ha policy: SWITCHOVER
vdc boot Order: 1
vdc create time: Sun Jul 31 17:39:25 2011
vdc reload count: 0
vdc restart count: 0
vdc type: Ethernet
vdc supported linecards: m1 m1xl

5. Non Stop Forwarding or Graceful restart
www.silantia.com5
 NX-OS has clear control and data plane separation.
 Allows Nexus device to remain in data path while routing process
restarts.
 Neighbors has to be NSF aware to achieve this.
 Restarting router sends signal to neighbors informing them it is
going thru a temp failure condition and neighboring routers starts
a grace period and continue to forward the traffic towards router
which has failure condition.

6. Graceful Restart for OSPFv2
www.silantia.com6
 When OSPFv2 needs to perform a graceful restart, it sends a
link-local opaque (type 9) grace LSA. The grace LSA includes a
grace period, which is a specified time that the neighbor OSPFv2
interfaces hold onto the LSAs from the restarting OSPFv2
interface.
 The participating neighbors, which are called NSF helpers, keep
all LSAs that originate from the restarting OSPFv2 interface as if
the interface was still adjacent. Note that interface has to be up
and operational during grace period.

7. Graceful Restart for OSPFv2
www.silantia.com7
Stateful restart is used in the following scenarios:
• First recovery attempt after the process experiences problems
• Inservice software upgrade ISSU
• User-initiated switchover using the system switchover command
Graceful restart is used in the following scenarios:
• Second recovery attempt after the process experiences problems within
a 4-minute interval
• Manual restart of the process using the restart ospf command
• Active supervisor removal
• Active supervisor reload using the reload module active-sup command
N7K(config)# router ospf CCEIDC
N7K(config-router)# graceful-restart
N7K(config-router)# graceful-restart grace-period 120

8. Graceful Restart for EIGRP
www.silantia.com8
The graceful restart-capable router uses Hello messages to notify its neighbors
that a graceful restart operation has started before restarting EIGRP.
During a switchover, EIGRP uses nonstop forwarding to continue forwarding
traffic based on the information in the FIB, and the system is not taken out of
the network topology.
Note again, interfaces running EIGRP should be operational during this period.
N7K(config)# router eigrp CCIEDC
N7K(config-router)# address-family ipv6 unicast
N7K(config-router-af)# graceful-restart
N7K(config-router-af)# timers nsf converge 180

9. NX-OS Troubleshooting
 Always gather problem specific show techs…..
N7010B-Dist# show tech ?
 In case you want to collect show tech use TAC PAC
N7010B-Dist# tac-pac
Above command collects show tech and saves a .gz file in
bootflash, you can use tftp to collect the file.
 Always get timestamp of the problem. Zip all files with NX-OS “gzip”
command before ship it.
 Use built in lnux tools eg.
grep, egrep, last, less, sed, wc, sort, diff, redirect,exclude, include, pi
pe etc. to look for specific information.
 Most useful commands
show version
show module
show log | last 100
show running-config ?
show system resource
show inventory
show interface transceiver
show core
show process log
dir bootflash:
show accounting log start-time 2011 Sep 20 00:00:00
show proc cpu sorted
show cli syntax | egrep “vpc”

10.  In 2008 SAN-OS is rebranded as NX-OS (from 4.0). NX-OS for
Nexus products are combination software components from IOS and
SAN OS.
 NX-OS is modular OS so if any process crash does not impact
overall operation of the switch.
 NX-OS was evolved from SAN-OS all necessary routing and
switching protocols are imported from IOS with completely rewriten
command line parser.
 Failed process creates core dumps.
N7010A-Dist# show core
VDC Module Instance Process-name PID Date(Year-
Month-Day Time)
--- ------ -------- --------------- ---- ----------
---------------
 To fetch the core dump from the supervisor.
N7010B-Dist# copy core:?
core: Enter URL "core://<module-number>/<process-
id>[/instance-num]"
N7010B-Dist# copy core: tftp:
NX-OS Troubleshooting crashes

11. NX-OS Troubleshooting crashes
N7010A-Dist# show system internal sysmgr service name l2fm
Service "l2fm" ("l2fm", 90):
UUID = 0x19A, PID = 4980, SAP = 221
State: SRV_STATE_HANDSHAKED (entered at time Sat
Sep 3 17:49:00 2011).
Restart count: 1
Time of last restart: Sat Sep 3 17:34:05 2011.
The service never crashed since the last reboot.
Tag = N/A
Plugin ID: 1
N7010A-Dist# show system internal sysmgr service pid 4433
Service "urib" ("urib", 173):
UUID = 0x111, PID = 4433, SAP = 427
State: SRV_STATE_HANDSHAKED (entered at time Sat
Sep 3 17:49:00 2011).
Restart count: 1
Time of last restart: Sat Sep 3 17:33:25 2011.
The service never crashed since the last reboot.
Tag = N/A
Plugin ID: 0

12. Troubleshooting NX-OS software upgrades
 3 types of software images - Kickstart, system and EPLD
 During the upgrade first supervisor gets upgraded to new
version of code then each line card gets upgraded
because line card also runs light weight version of NX-
OS.
 10 slot fully loaded chassis takes about an hour to
upgrade the code but during this period no traffic loss. All
configuration is locked on both sup.
 Before upgrading software check the software installation
impact
N7010B-Dist#show install all impact kickstart bootflash:n7000-s1-
kickstart.5.2.1.bin system bootflash:n7000-s1-dk9.5.2.1.bin
 In case software upgrade fails
N7010B-Dist# show install all failure-reason
N7010A-Dist# show process log
VDC Process PID Normal-exit Stack Core Log-create-time
--- --------------- ------ ----------- ----- ----- -------
1 installer 1497 N N N Sat Jul 16 22:29:59 2012
N7010B-Dist# show system internal log install | no-more
N7010B-Dist# show system internal log install details | no-more
 If available, gather bootup logs from console or from
CMP while software upgrade in process.
N7010A-Dist-cmp5# attach cp

13. F1 and M1 line card interactions
 All 32 ports in F1 series line card can work at 10 gig speed for local
switching (switching within line card) but total backplane available today is
only 230Gbps.
 F1 series line card requires M1 line cards to route a packet. All SVIs for
vlans in F1 line card are stored on M1 line cards (proxy routing). Port on M1
line card does not need to be up.
 F1 series line cards see other M1 series line card with a big giant port-
channel for each VDC and uses it for L3 lookups.
 F1 line card has connection between Forwarding engines so it can do local
switching without going thru switching Fabric.
 8 port M1 10 G line card can not perform local switching on first 4 ports to
other switch ports without going thru switching fabric because it does not
have the connections between forwarding engines.