cisco isr4k - routing in software or hardware ?

[carl_townshend]

Hi All

With routers like the ISR4Ks, are these all software based routers? or do they have asics in like switches and do routing in hardware ?

Cheers

[Giuseppe Larosa]

Hello Carl,

the ISR 4K can be considered in a hybrid status:

they are SW based routers for interfaces on the router, however they have a multiGiga internal fabric to connect to etherswitch modules or to service modules.

However, the Cisco licensing policies make the users to buy performance and boost licenses to use the total capacity of one device.

There are several threads about this issue the need to buy performance and boost licenses to achieve full throughput.

see the router selector for summary info

https://www.cisco.com/c/en/us/products/routers/router-comparison.html?product_id=41|42|43|44|45|46|57

I am not able to find the licenses info about ISR 4000 in this moment.

Hope to help

Giuseppe

[carl_townshend]

Hi Giuseppe

So in essence all the routing is software based? unlike a ASR which copies the FIB table to the QFP (hardware)

This is the reason we mainly use 9300 switches etc as they give much better L3 throughput for the money

[Leo Laohoo]

There are some network module the 9300 won't support. Example are DSL or LTE modules.

[Giuseppe Larosa]

Hello Carl,

you can use a multilayer switch instead of a SW based router if you don't need NAT, or as noted by Leo you don't need to use WAN access techonologies like xDSL or LTE / 3G mobile modems

For inter Vlan routing a multilayer switch is much more powerful because it works in hardware and as you noted is not so expensive.

Hope to help

Giuseppe

[Leo Laohoo]

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@Giuseppe Larosa wrote:

you can use a multilayer switch instead of a SW based router if you don't need NAT

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Catalyst 9300 (and also, maybe, 9400, 9500 & 9600) can/will support NAT:  CSCvp78589

[Giuseppe Larosa]

Hello Leo,

my sentence was generally speaking.

Up to now the only multilayer switch with NAT support in hardware was the C6500 /C7600 (C6800).

I don't know how difficult is to implement NAT in a switch TCAM.

if NAT will be supported on switches like C9300 it is an additional reason to choice them.

For sure switches that are proposed as replacement for C6500 like C9400 and C9600 should support NAT.

I have seen a thread sometimes ago of a user complaining about the lack of this feature in first shipment.

Best Regards

Giuseppe

[Joseph W. Doherty]

To OP, keep in mind with L3 switches and/or hardware assisted routers, you do need to be very careful of what is actually supported in hardware. For example, on a 6500/sup720 I setup a IPv6 GRE tunnel and discovered, although it worked, only the IPv4 GRE tunnel was supported in hardware. (It didn't take much IPv6 traffic to push the CPU up to 100%.)

One of the "gotchas" with L3 switches, since they do have special hardware to support normal/expected traffic, their CPU is often "weak" compared to even ISRs (as the L3 switch is only expected to handle control plane traffic). Further, LAN L3 switches (some of the Catalyst 9K series?) vs. MetroEthernet L3 switches, might be further lacking in some situations.

So in summary, although I believe the ISR 4K series is all software based, that's not true of all Cisco routers and it might change with any new models they add to the series, or a later/new ISR series. With routing capable L3 switches, what the switch supports, or not, can vary much. They all generally deal with "normal" traffic with dedicated hardware, it's the "corner cases" that can show a huge difference between specific models.

[Joseph W. Doherty]

I would say the ASRs might be a follow-on to the 7300s or 7200 architectures using the service engine. Basically, like those particular router models, the ASR has some additional hardware (your mentioned QFP) to "assist" the router. This provides additional capacity while keeping the full router feature set, although your "mileage might (much) vary" depending what you're actually doing.

The problem with L3 switches, they often give up some router features to provide their extra capacity performance. In addition to WAN modules and NAT, such L3 switches are often feature poorer in QoS. That said, as also noted by you, they provide much (much) more capacity for the money.