Chapter 7. Painless Software Upgrades
Juniper Networks recently added features to JUNOS software that dramatically reduce the impact of software upgrades on transit traffic by making it possible to upgrade the router operating system while the router is “in service.” In this chapter, we build on the pre-upgrade procedures discussed in the previous chapter and show how unified In-Service Software Upgrade (ISSU) functionality supports high availability goals.
Unified ISSU functionality applies only to platforms with redundant routing engines (REs). And since not all routers have redundant REs, this chapter examines software upgrades for platforms that support unified ISSU and software upgrades for platforms with a single RE or where a release of JUNOS supporting unified ISSU is not in use. Figure 7-1 shows the network topology that we’ll upgrade.
In Figure 7-1, routers
r5 and r6 have redundant REs and are platforms that
support ISSU functionality. Routers r1,
r2, r3, and r4 do not have redundant REs but are to some
extent paired so as to allow continuity of operations during OS upgrades
(i.e., r1 is paired with r2, and r3 with
r4).
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