Cisco 3845 Router maximum MPLS link bandwidth

[chetanyp1995]

Currently the 3845 router is connected over 80Mbps MPLS link wherein BGP Is running in full mesh

Will it support 150Mbps MPLS bandwidth?

[balaji.bandi]

As per i know this model support 250MB - by saying that also look how many routing table CPU process and RAM usage to get maximum processing.

[Joseph W. Doherty]

As @balaji.bandi correctly notes, the 3845 has a (Fast/CEF) switching rating of 250 Mbps (and 500 KPPS), but this is without any services!  BTW, the 3845's process switching bandwidth is listed at only 17.92 Mbps (and 35 KPPS), again, without services!  (NB: somewhat best and worst case maximum performance - still w/o services.)

I.e. depending on your traffic, and router configuration, performance capacity is quite variable.  (A rough rule of thumb, I've used for many years, is to use about 25% of the higher bandwidth rating as a "real world" estimate for max throughput.)

Oh, also (and a reason why 25% isn't as low as one might first assume), remember your 150 Mbps link, is likely that in BOTH directions, i.e. a possible aggregate of 300 Mbps of traffic.  (NB: the 250 Mbps, is for ALL traffic transiting the router.)

Assuming your router's config and traffic mix are not impacted, i.e. only about twice the traffic might transit your router.  What's your CPU load for your current traffic load?  You might also scale that (although router performance doesn't always simple linearly scale).

[chetanyp1995]

Hi Joseph,

Thanks for your reply. In reply to your last question - With the 80 mbps link CPU utilization is about 35 - 40 %.

However, even if we increase 150 MBPS the config part remains the same and no additional load will be added except the changed bandwidth (80 mbps to 150 mbps)

[balaji.bandi]

yes that load will be creased on the router, - it would be nice to observ the load when you add more bandwidth to system.

if you doing any NAT, the CPU load will be increased, so keep eye on it

and how it performing and any difference user and network point of view.

bare in mind the mode you mentioned EOL long back (it should work as long it can, since there is no support) - if this is critical to business, suggest to move to the model which has support.

[Joseph W. Doherty]

That may, or may not, be okay.  With the increased bandwidth, although your overall average load (you expect) to remain the same, the higher bandwidth link will allow more "intense microbursts".  I.e. your peak CPU utilization might jump.  If it hits 100%, router, may delay, and even possibly drop, some of your traffic.

As above, this is maybe okay or many not okay.  You can go ahead and try it.  Worst case, either have your provider reduce your bandwidth limits (which doesn't, necessarily, mean revert all the way back to 80 Mbps) or upgrade your router to a more powerful (higher capacity) model.

[chetanyp1995]

Okay...

Will go with this. Just one more thing I want to know, if we move on to 150 MBPS Link, can we forcefully use the speed of around 115 Mbps -120 Mbps instead of complete 150 Mbps? How ?

If you help me with above it would be really great help. Thanks in advance.

[Joseph W. Doherty]

Yes and no.

My mention of microbursts was more in mind of traffic being received on you higher bandwidth MPLS link.

If ingress traffic bursts overtax your router, ideally you can shape the "other side's" egress, to you.  This is probably not possible (i.e. your provider likely could do such, but providers often won't).

You might police your MPLS ingress, at a lower bandwidth, unsure whether this will help.  It might, it might not.

From what you've described, with your current average load, I would expect this possible issue to not be highly likely.  I.e. if it happens at all, it might just be so transient and of such short duration, it might even go unnoticed.

I just wanted you to be aware it might happen.