Cisco Catalyst 4500 Series, Software Configuration Manual

Page: 283 / 2086

5-57
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Chapter 5 Configuring Virtual Switching Systems
In-Service Software Upgrade (ISSU) on a VSS
Figure 5-9 Upgrading VSS System
Traffic and Network Protocol Disruption During ISSU in a VSS
Figure 5-9 indicates that both switches in a VSS reboot at some point during the upgrade process.
When a switch reboots, all the network links that terminate on that switch undergo a link-down event.
This means that network devices that are connected to the switch that is rebooting will observe a
disruption in service, unless the connection is over an MEC that contains at least one link that terminates
Active
(ver s ion X)
V S L
S t a nd b y
(ver s ion X)
Active
(ver s ion X)
V S L
(Re b oot)
Active
(ver s ion X)
V S L
S t a tef u l S witchover
S t a nd b y
(ver s ion Y)
(Re b oot)
V S L
Active
(ver s ion Y)
S t a nd b y
(ver s ion X)
V S L
Active
(ver s ion Y)
(Re b oot)
V S L
Active
(ver s ion Y)
S t a nd b y
(ver s ion Y)
V S L
Active
(ver s ion Y)
3
45707
Note th a t a t a ny given in s t a nt, a t le as t one of the s witche s i s Active. The Active
s witch i s in oper a tion, i.e. contin u e s to forw a rd tr a ffic a nd p a rticip a te in network
control protocol s thro u gho u t the d u r a tion of the u pgr a de oper a tion.