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Cisco Nexus 5596UP as a core switch: Design considerations

The Cisco Nexus 5596UP switch may be a better replacement for the Catalyst 6500 as a network core switch than the Nexus 7000, but there are design challenges to consider before investing.

Editor's note: The Cisco Nexus 5596UP switch is still being supported and marketed by Cisco. But in the five years...

since this tip was originally published, its capabilities have been incorporated and substantially upgraded within newer Cisco core switch families -- in particular, the Nexus 9000 Series. To that end, investment decisions concerning the Cisco Nexus 5596UP switch may not necessarily reflect current networking architecture demands.

In part one of this series on using the Cisco Nexus 5500 as a core switch, we explained why the Cisco Nexus 5500 -- in particular, the Nexus 5596UP --  may be a better choice than upgrading the Catalyst 6509 with a Supervisor 2T or a Nexus 7000. In part two, we look at Nexus 5500 design considerations that must be made prior to investing.

For engineers who need better performance than a Catalyst 6509 can handle, the Cisco Nexus 5596UP switch may be a less expensive alternative to the Nexus 7000. However, before you call up your local Cisco partner for a quote, below are some design considerations to note.

Migration path

If a Cisco 6509 densely populated with 10/100/1000 copper line cards is being replaced, the Cisco Nexus 5596UP switch does not offer a migration path for all of those 1 Gigabit Ethernet copper ports by itself.

Shops migrating from physical 1 GbE servers to 10 GbE blade centers with virtual hosts will probably not see this as an obstacle, as the transition from 6509 to 5596UP can move in lockstep with the virtualization project.

Fabric extenders

If 1 GbE copper ports are required for the long term, Cisco offers inexpensive Fabric Extenders (FEX) that can be plumbed to either a Nexus 5000 or 7000, and are bundled with optics.

A FEX is not a stand-alone switch; it would be more correct to think of a FEX as an external line card. Note that there are differences in the FEX architectures supported between the 5000 and the 7000. The 7000 has been behind the 5000 in FEX features and support, so check with your Cisco partner, as the state of this changes as new releases of NX-OS emerge. Also note that the Cisco Nexus 7000 switch does have a 48-port 10/100/1000 line card option, but a 7000 slot is an awfully expensive bit of real estate to fill with 1 GbE ports.

Uplink considerations

If FEX units are in use for top-of-rack, note that only eight of them can hang off of a Nexus 5596UP with the L3 module.

A 5596UP without the L3 module can handle 24 FEX. A Nexus 7000 series with compatible line cards can cope with 32 FEX. This affects shops using FEX as a part of the overall data center design, and it's a unique consideration. Stand-alone top-of-rack switches -- for example, the Catalyst 3750X -- have no such uplink limitations.

Redundancy

There is no redundant supervisor engine option in a Cisco Nexus 5596UP.

This means if the switch experiences a catastrophic fault, it becomes a failure point. However, a network core consisting of dual 5596UPs will presumably also have dual-homed FEX units -- if they are in use -- properly configured first-hop redundancy, a dynamic routing topology and a functioning virtual port channel domain with dual-homed uplinks.

These features -- among others -- are all recommended by Cisco in its documentation and design white papers as best practices to mitigate the risk of a single 5596UP going down and to make code upgrades nondisruptive.

Cisco Nexus 5596UP switch

Port density

The Cisco Nexus 5596UP switch can't expand port density like the 7009, which has finite expansion capabilities.

Therefore, long-term demand for additional 10 GbE ports will need to be considered -- not that a 7000 is the only choice for scaling 10 GbE port density.

Interface speeds

The Nexus 5596UP switch only supports interface speeds up to 10 GbE.

There is no migration path to 40 GbE or 100 GbE in a fixed-configuration switch like this. Today, 40 GbE is being used for uplinks from densely populated 10 GbE switches, and it's not expected to be a mainstream fixture in smaller data centers for many years.

In fact, there is still some debate in the industry as to whether enterprises will skip 40 GbE and go straight to 100 GbE when the time comes. Therefore, 40 GbE capability should probably not be part of the purchase decision, except for shops with IT hardware depreciation schedules greater than five years.

Next Steps

Read part one of this two-part series on Cisco's Nexus 5500 series

Cisco Nexus 9000 targets SDN deployments

Cisco improves Nexus lines for high-density 40/100 GbE

Cisco using open SDN technology to push Nexus switches

This was last published in March 2012

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How would a Cisco Nexus 5596UP switch improve your network's performance?
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The Layer 3 daughter card FEX limitations have changed. The new maximum FEXs per Cisco Nexus 5500 Series switch is 16 with the L3 daughter card installed: http://www.cisco.com/en/US/docs/switches/datacenter/nexus5000/sw/configuration_limits/limits_513/nexus_5000_config_limits_513.html#wp342041
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Not to forget: the N5K will never support MPLS (if you need that inside your core)
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