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Cisco Switch Routing

Mornincupofhate
By Mornincupofhate
in Networking
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Posted

So Cisco claims their switches can switch packets at line rate. If I buy a Cisco switch and use it as a router, will it be able to route packets at line rate?

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I don't know much about this kind of equipment, but to me "switch" does not mean "router".

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8 minutes ago, Jamiec1130 said:

I don't know much about this kind of equipment, but to me "switch" does not mean "router".

I've read some stuff and apparently you can make it act as a router.

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Some switches do have the capability to set up routing tables (I've been told this here as well), but they are probably not that efficient as compared to actual routers.

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What switch model?

 

The problem with turning a switch into a router is you tend to lose a lot of functionality for egressing the switch and going to the internet or see performance drastically reduced. Features such as NAT tend to not exist on switches, and a lot of traffic inspection and rules can slow things down a tad (depends a lot on the size of the rules and what's being inspected)

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Any layer 3 switch can run as a router to connect multiple subnets using routing tables. This can normally be done at line speed.

 

However what you are actually asking i think is can you use one as a internet router. The answer to that is no. To do that you need basic firewall and NAT functionality.

 

There are plenty of routers that can do gigbit routing, the trick is ones that can do NAT and full statefull firewall at gigbit.

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The only kind of routing for a layer 3 switch Cisco teaches has to do with Inter-VLAN routing. I would not set it up as your networks edge router

EDIT: Also like NZLaurence mentioned I dont think they support NAT which is a pretty big deal

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The ability to turn a switch into a router is only for the true, core definition of a router: A device that can route L3 packets based on destination address. L3 switches normally only support static routes, OSPF, RIP, and possibly EIGRP - they wouldn't support BGP, and they normally don't do much more of the functions of a "router". I've seen some that include a DHCP server (not just a DHCP proxy), but I've never seen a L3 switch that could do NAT or firewall.

 

As to the speed at which a L3 switch can handle routing data, that depends on whether the routing is done in hardware (like switching) or software, and the speed of the CPU if done in software. Thus it can vary greatly and use would have to request data from a sales engineer if it isn't available in the spec sheet.

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On 5/7/2017 at 5:25 PM, brwainer said:

The ability to turn a switch into a router is only for the true, core definition of a router: A device that can route L3 packets based on destination address. L3 switches normally only support static routes, OSPF, RIP, and possibly EIGRP - they wouldn't support BGP, and they normally don't do much more of the functions of a "router". I've seen some that include a DHCP server (not just a DHCP proxy), but I've never seen a L3 switch that could do NAT or firewall.

 

As to the speed at which a L3 switch can handle routing data, that depends on whether the routing is done in hardware (like switching) or software, and the speed of the CPU if done in software. Thus it can vary greatly and use would have to request data from a sales engineer if it isn't available in the spec sheet.

 

If you take my Cisco Catalyst 3750, it will only support EIGRP, RIP, or static routes, no OSPF or BGP.

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7 hours ago, droidrzrlover said:

If you take my Cisco Catalyst 3750, it will only support EIGRP, RIP, or static routes, no OSPF or BGP.

Depends on the image, IPBase doesn't support it but IPServices does/should.

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On 5/7/2017 at 4:49 PM, Mornincupofhate said:

I've read some stuff and apparently you can make it act as a router.

It's called a Multi-Layer switch.
It works at level 3 of the OSI model.

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On 5/9/2017 at 5:15 AM, Lurick said:

Depends on the image, IPBase doesn't support it but IPServices does/should.

True, I am only on IPBase

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